text:
Why are some transactions unavailable in my debug window?
I got a block and asked for the data in its first transaction and that generated an error.  The following is from the console tab in the Debug window:
10:52:52 getblock 000000000030bfd22ed67169b6bbf9ba994618fa9840642d395b56134f15176c

10:52:52
{
  "hash": "000000000030bfd22ed67169b6bbf9ba994618fa9840642d395b56134f15176c",
  "confirmations": 332460,
  "size": 216,
  "height": 81626,
  "version": 1,
  "merkleroot": "1ebda57ace225010d23d72619dbda5ee250dc4536f7c3428a9a419f06438ca54",
  "tx": [
    "1ebda57ace225010d23d72619dbda5ee250dc4536f7c3428a9a419f06438ca54"
  ],
  "time": 1285297753,
  "mediantime": 1285295165,
  "nonce": 71992579,
  "bits": "1b4766ed",
  "difficulty": 917.8307413015116,
  "chainwork": "00000000000000000000000000000000000000000000000000650ba70ddba016",
  "previousblockhash": "00000000001272fc0e0cfa9d08d854cfac681a939dccc21aecd9f7074fb0df2b",
  "nextblockhash": "00000000001bd5ac7329097b9888628c33c7adeecfc6e46f74fbab006f4c2127"
}

10:53:42 getrawtransaction 1ebda57ace225010d23d72619dbda5ee250dc4536f7c3428a9a419f06438ca54

10:53:42 No information available about transaction (code -5)

This happens in Bitcoin Classic and in Bitcoin Core.  I don't have a bitcoin.conf file in the folder where bitcoin-qt.exe lives, but I do have one where the chainstate and blocks folders are located.  It has five lines in it and each one starts with "addnode".

You need the transaction index enabled of you want to use getrawtransaction on arbitrary transactions. By default, only transactions that have unspent outputs are available.
Run bitcoind with -txindex or put txindex=1 in bitcoin.conf. You'll need to reindex.

I only do this to myself: Dave, RTFM! `getrawtransaction "txid" ( verbose )
NOTE: By default this function only works sometimes. This is when the tx is in the mempool
or there is an unspent output in the utxo for this transaction. To make it always work,
you need to maintain a transaction index, using the -txindex command line option.`

Hard to know without knowing your local machine state. My guess would be that you've downloaded the block headers (includes block information), but not the full blocks (which include transactions)

In that case, getblock would fail.


text:
Are there wallets that provide access to different HD wallets from the same masterseed using different passphrases?
I have a well-protected masterseed that I have not memorized, and memorizing it won't help since it could already be compromised.  My solution is to use a clever passphrase on top of that masterseed.  I've been looking around in Mycelium because I read somewhere that you can appear to access your bitcoin wallet and show any bad guys that it's empty by using an incorrect passphrase.  This makes so much sense that I want to do it, at least just for fun.
As I understand it, the masterseed encodes an integer which is the private key for a bitcoin address, and also a chunk of entropy that is used to generate the paths in the resulting HD wallet.  When a passphrase is used, the effect is to change the masterseed so that an entirely different HD wallet is the result.  So with one masterseed, you can have as many (invisible!) HD wallets as you want.  The feature required is the ability to restore from the masterseed plus passphrase.  Indeed, if the wallet is locked with the passphrase, then entering the wrong passphrase gives you a new wallet (and you'd have to realize on your own that you entered the wrong passphrase).
That is my dream: to be able to run Mycelium in front of a bad guy, enter my passphrase, and show that I have zero-balance.  An additional feature would be the option for old transactions to show up so that it still looks real, but like everything has been spent.
I have an Android with Mycelium, and I've looked at the cold storage and backup features (and the "Advanced" add-a-key feature) and I can't find a place where I can enter my 12 masterseed words PLUS passphrase and get a new wallet.  The only place I found like that is for cold-storage spending, and then it says "no funds found" (as expected).  It could at least give me a btc address so I could send some funds to my special secret passphrase address.

Yes! You can absolutely do this.
Trezor has this exact ability, on top of that you can actually use the device with your phone in Mycelium.
https://shop.trezor.io/
The setting must be activated, last firmware did not have it activated by default. This may have changed though.

If the Trezor is destroyed, do you have to buy a new one, or can you restore the wallet to Mycelium and then just use Mycelium?

You can restore the words to a different wallet. I am not sure which wallets can do the password on top of the seed though, you may have difficulty finding this extra feature.

Thanks MaxSan.  I did find that feature in Mycelium, but when I try to use it, it asks me to plug in my Trezor.  The only place in Mycelium where I found the ability to enter the words and a passphrase was in spending from cold storage, but it doesn't tell me the address from which it would spend, so I can't place funds in "cold storage" that I can spend that way, which is my ultimate goal.

You could also load it into other clients such as Bitcoin Core if you convert the seed phrase to a WIF-encoded extended private master key (112 byte base58 string starting with 'xprv')
Not sure if it offers a way to easily do that, such as dumpwallet in core, I wouldn't just go entering it into any webpage offering to convert it for you, but it's pretty easy, you can just checkout this code https://github.com/trezor/python-mnemonic and run something like this from the python3 console (this is the seed from the unit test so, if someone did send actual funds to one of its keys, it sure wasn't me, have at it)
$ python3
Python 3.8.1 (default, Dec 21 2019, 20:57:38)
>>> from mnemonic import mnemonic
>>> m = mnemonic.Mnemonic('english')
>>> sd = m.to_seed('bless cloud wheel regular tiny venue bird web grief security dignity zoo')
>>> m.to_hd_master_key(sd)
'xprv9s21ZrQH143K2oZcxUYy3fQGuVvxyVfs32imTuxjpVxzXMDA1phX18HGn8Ycsb1LjY9BuZmE4sqCJimiM7y6TVeh5feDcg6rHW8K5d8KNJb'

Then in Bitcoin Core, you could create a new wallet, run
sethdseed true "xprv9s21ZrQH143K2oZcxUYy3fQGuVvxyVfs32imTuxjpVxzXMDA1phX18HGn8Ycsb1LjY9BuZmE4sqCJimiM7y6TVeh5feDcg6rHW8K5d8KNJb"
in the console with the new wallet selected, and then set a password for it.

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text:
Wrong fee on transaction
I have sent a (>10000 byte) transaction to mtgox, blockinfo reports that the network fee is lower than recommended, so it will take quite a long while to get confirmed.
I was thinking I can send another transaction with more attractive fees - but that represents two difficulties:

I don't know why the client didn't calculate the correct fee
mtgox uses a single address per transaction, and so I won't get a new one until the current one completes.  If I send another transaction to the current address, when the slow one finally gets there, it will go to the wrong address.

I am not sure what is the best way forward.  I am using bitcoind v80500.
Is there a way I can get a transaction into mtgox without breaking the one I have currently waiting for confirmation, and if so, how can I get the fees to be right?

There is no correct fee for sending BTC to mtgox, and you can send to the same address. MtGox doesn't get the fee. MtGox only requires a number of confirmations. If you added a fee at all then there should be no extraordinary delay. A fee-related delay is for the first confirmation. The age of your source account(s) can make more difference than a fee. Just relax. The first time is painful to wait for.

I've updated...

I don't know how you can send a ">10000 byte" transaction to mtgox unless you are talking about the bytes of a raw transaction rather than a bitcoin amount. In that case, you should be able to figure this out. Send the same amount again from same addresses but with a higher fee. It is a double-spend and the network may take the second first while leaving the first to be discovered invalid.

I am referring to network fees, so I have updated the question.  The fee added to the transaction is small enough that it is very low priority and will take days to confirm.  What do you mean by "you can send to the same address?"

Sending the same amount from the same address is not a double-spend, you have to actually spend the same bitcoins.  It is just another transaction otherwise.  Yes I am talking about a large byte size transaction, which naturally needs a higher fee to process.

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text:
Encouraging virtual exchange and independance from hard money?
With all the talk of economic sustainability and the dangers of infinite growth how do you think a virtual currency could be used to encourage the trade of virtual goods ? Or possibly a more efficient use of natural resources.

I think this is more a topic for an essay, rather than a question answerable on a StackExchange.

It's not unusual that answers on StackExchange grow out to an essay, albeit Quora is even better at that :P Feel free I'd say!

I can reformulate to something more precise if you wish. Suggestions are welcome.

It won't be long before D.H. closes this question. I can bet on that!

Suggestions are welcome ?

I'm not sure I quite understand the question. What are the dangers of infinite growth?

Hi James, the bitcoin stackexchange is really designed for the types of questions where one answer can be clearly labelled "right".  Since this sounds more like an open-ended, everybody-give-your-opinion question, it's not really a good fit for this site and will probably be closed.


text:
How to interpret mtgox chart?
What is the difference between red and green rectangle?
And why there is 0% written in the chart?
And also, why is mtgox only focusing for 1 month and no more?
EDIT: The 0% in the chart appears only after loging in.

Green means the price increased during the relevant period, so the lower value is the opening price and the higher value is the closing price. Red is the other way around.
I think the 0% you see is a visual glitch. If you close the charts you'll see that right behind where you see this is the "Volume Discount Display" meter, which shows you how far along you are on the way to move up to the next discount tier. For some reason it is still displayed when the charts are open. (For me the value is different from 0%.)
For charts older than a month you can use for example http://bitcoincharts.com/charts/.

I have recently edited my question. Could you also make an actualization to your post? Thanks

@Comodore: Edited. If you agree that what I described is the problem, let me know so I can submit a bug report.


text:
How to move the blockchain data while still being able to use the wallet?
Using the standard client, Bitcoin-Qt, v0.8.1: (win10x64)
I would like to move the blockchain data from its default location to a different location (maybe even an external disk or NAS drive). What should I do to make this working while moving that data?

What operatng system?  Symlinks can help.

Asking about how to change the default storage location has been posted many, many times. The future canonical question is probably Bitcoin-Qt setup: Change block-chain file location, settings? documentation?. Possible duplicate of Bitcoin-Qt setup: Change block-chain file location, settings? documentation?.

This step-by-step how-to assumes you are using Windows 7 and installed Bitcoin-Qt to the default directory.

Make sure Bitcoin-Qt is not running
Create a desktop shortcut
Right click on the shortcut
Select Properties
In the "target" box, add -datadir="the new data directory"
Move everything in C:/Users/"your user name"/AppData/Roaming/Bitcoin/ to your new data directory.
Start Bitcoin-Qt with your new shortcut.

This moves the wallet too, which I think isn't what the asker wanted.

I do not want to move wallet file. Just chain, because it is growing too big you know.

Anybody know how to do this in linux ubuntu? Im going to run out of storage room before the blockchain synchronises. Its used 12 gig plus and still have 24 weeks to complete and I only have 2 gig left on my laptops hard drive and would like to store the blockchain on a removeable passport hard drive.

Perhaps this will help: http://bitcoin.stackexchange.com/questions/10551/how-do-i-specify-in-which-directory-bitcoin-blocks-and-other-data-should-be-stor

Except for the most recent file (which is being written to with each new incoming block), I believe you shouldn't have a problem in moving the other files with the wallet still open - aren't they read only?
Moving the last one, though, would probably require you to close the wallet even if just temporarily.


text:
Can the outputs of transactions with duplicate hashes be spent?
I've noticed that there are two transaction hashes that appear more than once in the blockchain. The reason for this is understandable: they sent mining rewards to the same address. These transactions had the same inputs (none) and the same outputs (one 50 BTC output to the specified address). However, this does cause a problem when you're trying to work with transaction data, as the transaction hashes cannot be considered unique identifiers of a transaction.
This was briefly discussed here, but the discussion was based more on block validity.
This actually led to a bug that caused an overwrite of the older transaction, which was fixed in the 0.6.0 release.
There were a few BitcoinTalk threads about one of these occurrences:
BitcoinTalk
Other BitcoinTalk
In the first of these threads, Gavin Andresen seems to suggest that the newer transaction's output can't be spent by saying "Ooh!  Ooh!  50 more bitcoins for the 'Bitcoins Lost Forever' thread!".
The two transaction hashes that have appeared more than once in the blockchain are:
d5d27987d2a3dfc724e359870c6644b40e497bdc0589a033220fe15429d88599
e3bf3d07d4b0375638d5f1db5255fe07ba2c4cb067cd81b84ee974b6585fb468
So, can these transaction outputs be spent? Why, or why not?
EDIT: I should mention that I checked, and as of July 5, 2013, none of the transactions' outputs have been spent.

Updated as my earlier answer was wrong
Quoting from BIP 0030:

Blocks are not allowed to contain a transaction whose identifier matches that of an earlier, not-fully-spent transaction in the same chain.
This rule is to be applied to all blocks whose timestamp is after a point in time

This means that a transaction can have the same hash multiple times as long as it's always spent first before the new transaction is created.
As for the older transactions: they are valid but the network won't let you spend them because the implementation in the reference client won't let you.

So, they can be spent in theory but not in practice (most likely)?

@Mike updated my answer with more concrete info


text:
How does Bitcoin Core's Coin Selection prevent change to be a dust output?
Bitcoin Core's Coin Selection optimizes for minimal change outputs. How does Bitcoin Core prevent Change outputs of sizes below dust threshold from occurring?

This question is wrong, as Bitcoin Core actually creates a minimum change of 0.01 BTC, if it can't produce a direct match.

See these lines:
// We do not move dust-change to fees, because the sender would end up paying more than requested.
// This would be against the purpose of the all-inclusive feature.
// So instead we raise the change and deduct from the recipient.
if (nSubtractFeeFromAmount > 0 && newTxOut.IsDust(::minRelayTxFee))
{
    CAmount nDust = newTxOut.GetDustThreshold(::minRelayTxFee) - newTxOut.nValue;
    newTxOut.nValue += nDust; // raise change until no more dust
    for (unsigned int i = 0; i < vecSend.size(); i++) // subtract from first recipient
    {
        if (vecSend[i].fSubtractFeeFromAmount)
        {
            txNew.vout[i].nValue -= nDust;
            if (txNew.vout[i].IsDust(::minRelayTxFee))
            {
                strFailReason = _("The transaction amount is too small to send after the fee has been deducted");
                return false;
            }
            break;
        }
    }
}

So Bitcoin core will give slightly less to the recipient rather than spend more than the payer originally requested, in the case of a dust-change output.

Then there's the question of whether or not this is a good policy... I don't believe it is. I think that as infrequently as dust change happens, just let miners have it and get a slightly faster confirmation time.

It might not be good network policy, but it doesn't seem like users have an incentive to destroy dust UTXO's sent to them.

Bitcoin Core actually creates a minimum change of 0.01 BTC (if it has sufficient funds), if it can't produce a direct match.
In the rare case that it doesn't have sufficient funds to produce a non-dust change output, it will do the weird stuff Stephen mentions.


text:
Why do transactions get verified before it is clear that the block header is valid?
When I researched for the answer on What happens in detail, when Bitcoin Core verifies a block during synchronization?, I noticed something:
According to the Wiki-Entry on Protocol rules some of the transactions' traits are checked before all header data is verified.
Why do the following checks of difficulty statement and timestamp get performed only after transactions get looked at?

Check if prev block (matching prev hash) is in main branch or side branches. If not, add this to orphan blocks, then query peer we got this from for 1st missing orphan block in prev chain; done with block
Check that nBits value matches the difficulty rules
Reject if timestamp is the median time of the last 11 blocks or before

Wouldn't it be more efficient to check the relation to the main chain and timestamp first, and then check the legality of the transactions?

Seems like in the normal case, all this work has to be done anyway, so it really doesn't matter what order you do it in.  It's true that if the block header were invalid, you could skip checking the transactions, but this should be very rare since you normally only get a block from another node who has already verified it.  My guess is that this is just something that nobody bothered to optimize - but feel free to submit a pull request :-)

That seems a likely explanation. :)

With that sort of wiki page it is almost certainly not correct too, the wiki is rotten to the point of complete uselessness in a lot of cases.

Good point. The wiki page hasn't been edited since May 2014, it may well be outdated.


text:
How is wallet at official client encrypted? What encryption it use?
How is wallet at official client encrypted? What encryption it use?
What encryption does Bitcoin-qt use and what encryption is used at Multibit?
And how strong that encryption is compared to other methods?

Both bitcoind and bitcoinj use AES-256 encryption for the private keys in their wallets (this does not mean that the wallet formats are compatible though).
Bitcoin-Qt is just a GUI on top of bitcoind and Multibit is using bitcoinj internally, so the same should apply to them.
References:

comment in the bitcoind source code
bitcoinj documentation

what strength of AES?

If by strength you mean key length it's 256 bit in both cases.

ok, please add it to the post and add information how long does it take to crack it by supercomputers and how can quantum cryptography break that stuff.

I don't know and I think this would be off-topic for this site. But I'm pretty sure you'll find the answer on [crypto.se].


text:
Where can I buy bitcoins from Ireland without photo ID?
My available methods of payment would be laser(Ireland debit card scheme), mastercard, visa or a bank transfer.
I'm a beginner user in Ireland.
I'd also prefer not to have to verify my account with a photo ID.
I won't be spending large sums of money either so the cheaper the better, and the money will be spent pretty much instantly so i'm not too worried about having THE most secure option if it means i'd have to pay more.
Thanks!

possible duplicate of How do you obtain bitcoins?

I've been using Intersango's service lately, and am happy with it. You can deposit by SEPA bank transfer, no ID required.

As you are not wanting to get verified by ID, the Mt.Gox option is not possible.
This page would provide you some information:
http://www.btcwallet.org/contact/fill-up-your-wallet-buy-bitcoins-option-one/
This 1. option is trading which is quite dangerous, you´d better read this before:

http://wiki.bitcoin-otc.com/wiki/OTC_Rating_System
http://wiki.bitcoin-otc.com/wiki/Using_bitcoin-otc%23Safety:_avoiding_fraud

And the similiar way but I think the easier one would be bitcoinary
But firstly you should check if there is someone near you at localbitcoins
You might also consider using up your EUR account and then using SEPA to deposit to bitstamp, which is probably best europe exchange with good support.

LocalBitcoins.com and local cash trade guarantees maximum anomity. Do not use online payment if you want to remain anonymous.

Eircoin.net is one option I used before. The response was prompt and the whole transaction (despite a mistake on my part) went almost instantaneous.
Localbitcoins is another possibility if you want to trade in cash within your neighbourhood.

https://quickbitcoin.co.uk/ are based in the UK, and accept bank transfers from any bank within the faster payments network - that includes many Irish banks.

You can find friends of friends that trade crypto currency at https://www.cointouch.com/
No fees or ID verification. Very easy to get started.

I have used Aurumxchange.com
for SEPA transfers. Buy their VouchX with and then redeem them on any of the exchanges suppporting them, e.g. you can redeem them without fees at Vircurex.com

I have used irishbitcoins and they where very fast, I have only used the deposit method once but I wasn't asked for ID. The guy even met me in Dublin the next week and i got more from him, sound lad. sure send them an email and see.


text:
How does Dash achieve anonymity without centralisation?
Dash is supposedly completely anonymous. How does this work without any centralisation? Is there one person with all the transactions and only they mine?

I don't think Darkcoin lives up to its promises of anonymity. 2) No, darkcoin is not centralized.

Dash already made a lot of changes since its inception. Now on testnet you can achieve probably the fastest mixing with PrivateSend ever. It takes only hours to have up to 2000 Dash ready for PrivateSend. It will be live on mainnet with many other updates in less than two months.

TL;DR yes, it's still decentralized, no it isn't perfectly anonymous.
From the Darkcoin (now Dash) Wikipedia: "It adds privacy to transactions by combining identical inputs from multiple users into a single transaction with several outputs. Due to the identical inputs, transactions usually cannot be directly traced, obfuscating the flow of funds." The nodes who perform this "mixing" are called Masternodes, and operate on a decentralized ledger.These nodes are trustless and do not have complete knowledge of input/output
In order to prevent Sybil attack, the masternode tier requires colateral of 1000 Dash to run. This makes the cost of attack very big. In this whitepaper is a lot more information for interested ones.

Doesn't the amount of coin reveal any information? If the outputs matches the input, it reveals in the mixing process and correlates the inputs to the outputs. How can this be prevented?

From the wiki: "combining identical inputs from multiple users into a single transaction with several outputs. Due to the identical inputs, transactions usually cannot be directly traced, obfuscating the flow of funds." However, there are claims to be able to trace transactions, so it seems likely that Dash is not perfectly anonymous.

I suppose it could be called semi decentralized, as if those privileged nodes are cut off from the network, then remaining nodes are unable to mix.


text:
Parameters for buy order on BTC-E
Using the BTC-E API 'm getting an error of You incorrectly entered one of fields. when I post this as the data in a buy order.
{'pair': 'btc_usd', 'amount': 0.1, 'rate': 44.7084704, 'type': 'buy', 'method': 'Trade'}

Does anyone know where I'm going wrong?

Problem solved. The error is caused by too many decimal places in the rate parameter. It would be good if the API returned a more informative error message though.
There is an API call to find the correct maximum number of places, as well as the minimum order for each currency pair. https://btc-e.com/api/3/info returns a list of currencies and information. The documentation is in Russian but translates easily with Google Translate.

got this error too. looks like correct number of decimal places is 5 or 6 (I tested on LTC)


text:
How is a hard fork resolved?
In March 2013 there was a fork following the v0.8 release. The issue was resolved rather efficiently, as explained in the post-mortem report. However in this process there were winners and losers: the miners building on the v0.8 chain had to give up their block creation fee.
The next time there's a fork like this, it may not be so straightforward. The miners may not all agree on the proper resolution for the issue.
Is there any documented set of rules (bye-laws) explaining how such forks are to be resolved in the future?
If there's a conflict among the parties involved, who has the final say?
PS: Any comments on Bitcoin's so-called (faux) "decentralized" architecture are also welcome, given my other question has been censored. The decentralization doesn't seem to work after all, which begs the question as to what the whole point of the proof-of-work scheme is anyway.

A hard fork is by definition one that does not get solved. At least not by the rules of the system, as it is essentially an incompatibility between the rules assumed by separate nodes.
But think about what can cause such a thing:

An incorrect (=not identical to the rest of the network) implementation forks off. In this case it will always certainly be clear who is "at fault". For example, in the 0.7 vs 0.8 fork, there was a bug in the 0.7 (and older) clients that limited them in an unknown way, but 0.8 was at fault for not correctly mimicking the bug. As keeping such a weird and inconsistent limitation would hold the network back, and be risky in itself, the bug-free behavior will become allowed after may 15. However, if old full clients remain on the network after that date, they will end up on a fork, and this fork will not resolve.
Two implementations arise that knowingly implement different rules, perhaps because of ideological disagreement about what the rules should be. If both are economically significant and have significant mining behind them (which in neither case necessarily means a near-majority), this is pretty much a disaster. The incentive for consensus is huge, as disagreement effectively means granting every old coin hold to spend it once on each side.

Regarding decentralization, I think you mistake consensus for centralization. There are of course degrees, but ultimately it is Bitcoin's users who decide which rules to enforce by the software they run. However, as explained, there is a huge incentive for making sure no real disagreement arises. In some cases that may mean discussion will be needed, and an agreement has to be reached, perhaps a compromise. But it doesn't mean one party gets to control others.

"I think you mistake consensus for centralization." How does one achieve consensus among a million nodes without deferring to a few (elected) representatives? By that logic, all currency issued by a democratically elected government is decentralized. It's "decentralized plus consensus," you might say, and (oh!) it can always be forked. That makes Bitcoin no different.

Well if no consensus can be reached (by whatever means), then the default is that the rules stay the same. If people refuse the change their software, perhaps by disagreeing with what their 'elected representatives' decided, and even if they are a minority, then moving forward with a change is suicide for the system. And as the system matures, the need for changes to the rules will hopefully decrease as well.

You're right, of course, but the same could be achieved with a more honest centralized-but-distributed design. People could still fork the ledger if they didn't like the rules. Advantages: no 51% attack, faster transaction processing, energy-efficient, etc. It's not clear what is achieved by Bitcoin's proof-of-work other than to give the false appearance of being decentralized.

"... then moving forward with a change is suicide for the system." This is an article of faith in the Bitcoin community. Real life experience with fiat currencies suggests otherwise. If the US Federal Reserve printed any more money, it would be "suicide for the system," but alas no one really cares (more interested in Kim Kardashian). No one cared when Nixon went off gold in 1971. http://en.wikipedia.org/wiki/Nixon_Shock

@Manish not sure why you're taking such an antagonistic tone--people are here to answer questions about Bitcoin, not to "defend it". Nonetheless I think even a quick glance through the development mailing list will show that there's no one in the Bitcoin community with power at all approaching that of a central government. Specifically with the March 2014 fork you'll note that Gavin's first suggestion wasn't the ultimate course of action. But consensus in the face of a glitch is easy. More important is the fact that despite multiple clients and four years of development, the only hard forks

have been due to glitches. Bitcoin is distributed precisely because the technology is stable enough not to need regular decisions from the community about who to follow. Any significant technical change would require something Nixon never had--an advance supermajority of consensus. Otherwise no would care about a proposed change in the first place, and no one would bother downloading any new client which implemented it because the change is too controversial. The community trusts developers to fix glitches, not make radical protocol changes.

"... then moving forward with a change is suicide for the system.". I don't mean this in the political sense. It's economic suicide for a currency if every coin can suddenly be spent twice, once on each side of a fork.

What baffles me is that in all technical explanations I read so far its said that the longest blockchain is automatically accepted. But in reality this doesn't seem to be the case, right? So when the protocol says to automatically accept the longest blockchain but in reality it doesn't happen, doesn't that mean that the protocol is not fully implemented at this point?

The rule is that the longest valid blockchain is accepted. A hard fork is when for some reason (usually unintentionally) two sets of nodes disagree about what is valid.

The core concept has always been accept the largest blockchain that passes the predetermined proof of work tests. Hard forks like the one that occurred in March happen as a result of some software in the p2p ecosystem having a different understanding of what the legitimate blockchain should be. This reality is ok with all distributive networks to some extent and usually gets resolved rather quickly and in many cases autonomously
Yet march was special in that the 0.8 clients could never agree with the 0.7 clients due an issue processing a larger than normal transaction volume, but 0.7 clients still had 60% or so of the total hash power. In essence the network had two different legitimate bitcoins floating about. Your question was who got to decide which one was the legitimate chain and what happened to the coins?
BTCGuild and Slush got to decide as they collectively control over 51% of the network's hash power. And also some people had to accept that the blocks in the orphan fork had to be lost for the good of Bitcoin. It isn't necessarily fair. It isn't fun. But Gavin and others handled it both quickly and transparently.

The next time there's a fork like this, it may not be so
  straightforward. The miners may not all agree on the proper resolution
  for the issue.

This is a valid concern and is something we accept as a community to be an issue. Generally speaking people tend to be self-interested and miners have a vested interest in preserving the value of Bitcoin. Thus always assume behavior will be economically motivated as Satoshi did in his paper discussing honest nodes.

Is there any documented set of rules (bye-laws) explaining how such
  forks are to be resolved in the future?

No and there will never be because that implies an organization asserts the right to prescribe behavior in the community, which defeats the whole point of having a decentralized p2p currency. Only when pool operators decide to group up with more than 51% hash power can they make decisions for Bitcoin. This rarely happens unless an event like March occurs that could damage the integrity of the entire system

If there's a conflict among the parties involved, who has the final
  say?

Whoever has 51% hash power.

PS: Any comments on Bitcoin's so-called (faux) "decentralized"
  architecture are also welcome, given my other question has been
  censored. The decentralization doesn't seem to work after all, which
  begs the question as to what the whole point of the proof-of-work
  scheme is anyway.

I've been censored as well and no bitcoin is currently not decentralized as envisioned. I mention this in my Bitcoin course using the notion of oligarchiness as a measure of central control. There are a handful of very influential people currently developing and maintaining the bitcoin ecosystem. They have a dramatic say in how the money works and the software to use it. Over time as more actors enter the marketplace and nation states begin to use Bitcoin, this will be reduced until eventually no one party has control.
Remember that at one time Satoshi had 100% of all bitcoins in circulation and the software running the network. We have made wonderful strides over the past 4 years and will continue to do so over the next 4 years.

Those who will buy the coins from the miners are the ones who guide the miner's behavior.
This is called the economic majority.
At the level of maturity of the Bitcoin economy in March, 2013, the decision as to what the economic majority wanted was the response to a very short question: "What side of the fork is Mt. Gox on?"
The answer to that was that Mt. Gox was still using the v0.7 client.  That response alone was enough to instantly know the will of the economic majority.  Until there isn't a single exchange holding the vast majority of economic value, then simply that one exchange is the decider.
Now if, for instance, BTC Guild's miners didn't want to abandon the v0.8 side of the fork, they could have switched to other pools such as Slush's (which was still on the v0.8 side) or switched to P2Pool, etc., and continued mining on the v0.8 sid.e  Then there wouldn't have been enough hashing on the pre-v0.8 side to cause that to become the longest chain.  But if Mt. Gox were to have held firm with v0.7, the newly mined coins would not been spendable and eventually miners would likely have defected to the v0.7 side eventually.
If Mt. Gox had been using the v0.8 client already, the hard fork issue would have been resolved likely by new configuration settings (or a patch) to previous releases being released to fix the newly re-discovered limitation that had existed with all pre-v0.8 clients.

Though it was BTCGuild suggesting to switch to 0.7 to resolve the fork, and this was indeed after asking Mt.Gox what they were using, we (several people in #bitcoin-dev at the time, including me) immediately agreed that was the best solution. I can't speak for others, but for myself that had nothing to do with Mt.Gox, but simply with the fact this was the only solution that didn't require an immediate hard fork of the network.


text:
What is the best way to implement micropayments with Ripple?
I'm interested in the following use cases:

Web content
Voice and media traffic

For the first case, it would be ideal to be able to include some sort of proof in a custom HTTP request header showing that the client has made the payment. The server should be able to check this proof and verify that the payment has indeed been made, and then reply with the requested resource or return an error.
It may be a payment (required), or it may be a donation/tip (voluntary); in the latter case the server may collect these and verify them later.
For the voice and media case, the idea is to incentivize independent relay nodes to forward traffic for clients behind NAT/firewall or simply those who wish to add a layer of anonymity (similar to Tor). Again, these could be "metered" payments (e.g. 0.0001 XRP per 10 MB, or say for 30 minutes), or they could be tips. The speed would be extremely important in this case.
As I understand it, there are two ways to do micropayments:

On-ledger: These are payments made on the ledger and verified by the recipient using the transaction ID. This may be too slow, depending on the use case.
Signed transactions: Here the sender simply sends a signed transaction to the recipient, who can verify instantly if the sender has sufficient funds. Double-spending is possible in this case.

What would be ideal is if we could generate some sort of bearer token that could be passed around over multiple payments before it is finally redeemed on the ledger.
It would be even more awesome if these bearer tokens were anonymized using blind signatures.
Has anyone implemented micropayments with Ripple, and are there any guidelines/recommendations on how to go about it?

Pre-signed transactions won't work the way you want due to how Ripple uses a simple sequence number. The only downside to doing small transactions via Ripple is the 0.000010 XRP transaction fee and the 2-20 seconds (or so) delay between signed ledgers.
Normally a merchant generates the payment information. E.g. "send 1 USD to account A, destination tag 123 (any 32 bit number), invoice ID 0x12345678 (256 bits of data)", often this would be with a Ripple URI (note that page doesn't document how or if an invoice id can be specified in a Ripple URI). The customer then selects the URI and is taken to the send page in their configured client (currently now always ripple.com/client) with all that information pre-filled in. The merchant then listens on their connection to a Ripple server (either local or remote) for information on payments to their account and uses the destination tag and/or invoice id to update payment status for individual customers or invoices. Normally merchants should handle the possibilities of one invoice being paid via multiple transactions and overpayments or the like as well.
You could have the customer provide the transaction hash(es) as you suggest, but that's not normally done and is usually more work for the customer for no reason.

Thanks, that partially answers my question on how to do it on the ledger. I think 2-20 seconds is too slow for micropayments. It has to be less than a second. If an issuer on the Ripple network could issue a token (preferably with blinding) that could be later redeemed on the ledger, that would be most ideal.


text:
The Bitcoin-Gold fork came before I expected.... can I still access my BTG?
I transferred btc from gemini to a paper wallet around at 9:30pm Monday. Will I still be able to get my BTG? Where will they show up? I'm not sure when the "snapshot" was created.

According to this article, Bitcoin-Gold forked "at block 491,407 on the original blockchain".
If you look up your sending or receiving address in blockchain.info, and drill down into the transaction id, you should be able to find the block number that it was included in. This will allow you to work out whether your transaction was before or after the fork.
If you have access to the private key of an address where bitcoins were stored at the time of the fork, you should be able to get the BTG and the BTC as you have full control of them.
However, I believe Gemini is an exchange, so if you have bitcoins stored on the exchange at the time of the fork you'll be relying on them to give you any BTG you would otherwise have access to (assuming they don't give you access to the private key of the funds stored on the site... but exchanges usually don't).
Note that on 8th Oct 2017, Gemini announced on Twitter that they would allow users to withdraw Bitcoin-Cash, which was created as a fork of Bitcoin in a similar way to Bitcoin-Gold. Perhaps this is a good indication they will do the same for Bitcoin-Gold.

Note that a new answer was added to this question stating "Yes all of that is true. Many thanks. What I am asking is... Do we know if gemini exchange will be crediting wallets with btg Yes I had some btc on gemini at the time of the fork". This was probably not able to be posted as a comment due to the users reputation, so I've posted it here.

@Some-guy, I've edited my answer with some information that might help.


text:
How to access Blockchain remotely for statistics study?
I would like to write small paper supported by Blockchain stats.
Could you tell me how to access blocks chain remotely via GUI to make a query ?
Blockchain's size is 159GB as of today, so download is heavy.
Ok, I can study block headers only to limit overheads.
Do you know how to download or access blockchain headers as mySQL database ?
How to access Blockchain remotely for statistics study ?

Ok, I can limit my interest to block headers only to create  database.
https://blockchain.info/block-height/474044?format=json  So all I need is block header from the above block. Any download link ? Studied blockchain json API but no support for block header only.

https://blockchain.info/block-height/491459  is the answer but output is not generated via API, so I need raw json block header output, not full webpage code included

As you mention in your comments, blockchain.info can provide this information.
You can get a raw block in JSON format using the /rawblock/ links, for example:
https://blockchain.info/rawblock/0000000000000000008d49f25f7dd5d3704575a348e030a1d2e5f396b3e80516
Then you can also get it as the hex-encoded raw block by adding ?format=hex to the url:
https://blockchain.info/rawblock/0000000000000000008d49f25f7dd5d3704575a348e030a1d2e5f396b3e80516?format=hex
Hope that's what you are after :)
EDIT: Oh, just re-read your comment, you want just the headers? In that case you probably can't use blockchain.info, you could try BlockCyhper instead:
For example: https://api.blockcypher.com/v1/btc/main/blocks/294322
You can find more info about their API here: https://www.blockcypher.com/dev/bitcoin/#blockchain-api

thank you MeshCollider for your excellent answer.  At first view block headers by blockcypher and by blockchain look the same but blockcypher sets nonce to "0" . I have no tools to verify if other data in the block header are reliable generate charts for my paper   Just have a look: https://blockchain.info/block-height/491658  vs.  https://api.blockcypher.com/v1/btc/main/blocks/491658 or https://api.blockcypher.com/v1/btc/main/blocks/294322 nonce always set to "0" so what you get is not valid blopck header


text:
If the computer calculation rate becomes 100x faster, would the value of bitcoin drop to 1% of the previous value?
This is my main concern, but are there any other design flaws with Bitcoin?

TL;DR: Change of computer calculation power doesn't affect the price at all.
Market Price of anything determined by supply and demand, bitcoin is not exception the only difference is that the supply side is constant, 50 BTC per ten minutes at the moment. Regardless of how much computer power used to generate bitcoins the rate of produced bitcoins will not change because Bitcoin network difficulty will adjust to make it harder or easier to find new bitcoins depending on total network computer power, bitcoin price change purely because of change of demand.
Also there is a controversy about certain aspects of Bitcoin, but there is no designing flaws that I know of.

Thanks for clear it out, now I have more confident about it

7,200 BTC a day is mined whether there is 200 rigs hashing away or 20,000.
The rate can climb slightly but every 2,016 blocks the rate of issuance gets recalibrated back to being once every 10 minutes (at 50 BTC per block then is 7,200 BTC per day).
The block reward subsidy will be changing in a couple months, to 25 BTC per day so the daily issuance is going to drop suddenly by half, for the next four years after.


text:
How many coins are needed to ensure stability i.e. neither inflation nor deflation?
The key to currency stability is to have neither too many nor too few of a currency in circulation. So what is the "Goldilocks" area going to be if Bitcoin really catches on and everybody wants to use it?
Could it turn out that demand will outstrip supply of the coins, resulting in inflation? Has this already happened?
It seems to me that if a popular retailer like Newegg were to begin accepting Bitcoins then this could cause a spike in use and inflation.

This question has several assumptions that are wrong, there is an excellent interview about Bitcoin that I think you should watch https://www.youtube.com/watch?v=OtN9YUvh_XM

A spike in use would cause deflation.

Has demand already outstripped supply?
Yes, in fact it happens hundreds of times each day.  The evidence of this happening comes with each uptick on the market price ticker.
What I mean by that is that with a currency that floats there is a limited supply at a certain price point.  Once those are sold and no new sellers wish to sell at that price, then those representing demand will consider buying the supply that is offered at a higher price.  When that happens, demand has outstripped the supply at the lower price.
Now some people use Bitcoin as a payment system without holding coins themselves.  So for them, it doesn't matter what the exchange rate is.  If they are to send $50 worth of bitcoins today, it costs them about $50-ish to buy the coins and to send them.   A year from now, to send $50 worth of bitcoins, it too will cost about $50-ish to buy the coins and send them then as well.
So the ones who will be impacted by the fluctuations in the exchange rate are those who hold the coins.  These include speculators.  Though speculators do use the Bitcoin network to transfer funds, their transaction aren't necessarily supporting the Bitcoin economy -- they are simply speculative flows.
Merchants too can have their proceeds from sales converted to fiat so as to avoid exchange rate risk.
So even though there is and will continue to be exchange rate volatility (or price inflation and price deflation for product pricing), those preferring to not be exposed to that risk can easily avoid it.
As far as exchange rate volatility affecting prices, technology has already mostly solved this problem.  A customer traveling in a foreign country can check prices using a currency conversion app on a mobile, for instance.  The merchant generally deals only with the local currency but at checkout the amount is converted to the customer's currency using a conversion rate.  There's no reason Bitcoin needs to be treated any differently than being just another foreign currency.
The amount of currency that exists at any point in time at the present and future is known, so that should lessen the amount of fluctuation that comes from market uncertainty over whether or not monetary policy will be inflationary or not.
Knowing the currency won't be debased adds to Bitcoin's stability.

This question would be better for Economics SE, if it was still around. But oh well.
You can't really prevent short-term inflation and deflation spikes, as anyone with substantial enough money supply could sway the economy until it balances itself out. Also, a similarly rich person could cause the Bitcoin to rise and fall in value in a pump-and-dump cycle by buying Bitcoins over a long period of time, and then spending them all at once for profit. Rinse, repeat.
For a long term, you'd need to generate Bitcoins at the same rate as the Bitcoin economy grows. As the value would be really hard to estimate, setting it in advance would be impossible.
The main way I can see Bitcoin having a stable-ish value while allowing for the economy to grow and shrink would be through the use of a system akin to Digital Coin. Generally, the idea is that everyone could be creating their own currency that would be exchangeable for Bitcoin at a varying rate. The rate would vary based on the supply and demand of the private currency. There are a few mechanics to encourage people to use the private currencies, which I won't go into detail here. In this scenario, Bitcoin will be used as a standard of value - meaning everything will be compared to Bitcoin, but actual Bitcoins wouldn't be spend under normal circumstances. This way, Bitcoin in most cases wouldn't undergo inflation, but the economy built around it could.

There is a quantitative finance SE in beta now, that might work.

I'm running a bitcoin with inflation experiment to find out the answer. https://github.com/bitflate/bitflate


text:
Is quickbitcoins.net reputable?
Mailed in cash with postal envelope. Website started acknowledging receipt via postal delivery 3 weeks since. Blockchain within 3 hours of "caught up". Yet no bitcoins.
Is it a scam?
Cash amount was small, should not pose problem. Was what you call "pilot test" and had bitcoins arrived promptly would be followed with larger purchase.

I don't know of a problem with them. Did you check at http://blockchain.info/ if your address has received coins? What do quickbitcoins have to say on the matter?

They provide a phone # on a post on this thread: http://bitcointalk.org/index.php?topic=92026.msg1239487#msg1239487

Burner cellphone too expensive to inquire 50 euros.

Ok, well then you could post a reply in that thread or PM to the forum user.

While QuickBitcoins may offer to accept cash via mail, sending cash in the mail is generally considered an inadvisable activity due to the high likelihood that your mail will be "lost" by a dishonest person handling the mail somewhere along the delivery path.

Anonymousness more important than occasional stolen envelopes. Website confirms payment received, but no bitcoins have arrived.

I used quickbitcoins.net successfully 4 times. They are gone now. The 800 number is disconnected and their e-mail address returns nothing. Try to find the http: website on Explorer or on tor and neither can find it! Site no longer exists! If you send coins to them without checking you will loose your money!

See http://bitcoin-otc.com/viewratingdetail.php?nick=QuickBitcoins
The owner of QuickBitcoins and his wife have been on #bitcoin-otc for quite some time. I've had successful trades with them before they ran QuickBitcoins, but never through the site itself.
For any problem you might be having with the site, I'd definitely recommend contacting them. In my anecdotal experience, Aethero (the site's operator) and lucidlepidoptera (his wife) have had great communication. Try info@quickbitcoins.net, or jump on IRC and go to #bitcoin-otc on freenode.net. They're usually there with the nickname "QuickBitcoins".

We're very sorry about this experience. At the moment it doesn't look like we have any open cash in mail orders so either we have 1) Filled this order or 2) Not received the cash. Please feel free to email us at info@quickbitcoins.net or call us any time at 1-888-959-3166 to work out where the problem is. Please make sure to reference your order number.

Email has been transmitted. Please be checking spam folder.

Someone who asks you for money but hides his identity, is automatically non-reputable, almost by definition...
looris@Palace-of-the-Nine-Moons:~ $ whois quickbitcoins.net

Whois Server Version 2.0

Domain names in the .com and .net domains can now be registered
with many different competing registrars. Go to http://www.internic.net
for detailed information.

   Domain Name: QUICKBITCOINS.NET
   Registrar: ENOM, INC.
   Whois Server: whois.enom.com
   Referral URL: http://www.enom.com
   Name Server: DNS1.REGISTRAR-SERVERS.COM
   Name Server: DNS2.REGISTRAR-SERVERS.COM
   Name Server: DNS3.REGISTRAR-SERVERS.COM
   Name Server: DNS4.REGISTRAR-SERVERS.COM
   Name Server: DNS5.REGISTRAR-SERVERS.COM
   Status: clientTransferProhibited
   Updated Date: 02-jul-2012
   Creation Date: 29-apr-2012
   Expiration Date: 29-apr-2013

>>> Last update of whois database: Thu, 24 Jan 2013 08:56:40 UTC <<<

[...]

=-=-=-=

Registration Service Provided By: Namecheap.com
Contact: support@namecheap.com
Visit: http://namecheap.com

Domain name: quickbitcoins.net

Registrant Contact:
   WhoisGuard
   WhoisGuard Protected ()

   Fax:
   11400 W. Olympic Blvd. Suite 200
   Los Angeles, CA 90064
   US

Administrative Contact:
   WhoisGuard
   WhoisGuard Protected (f1523859958c4c18a48b1813ac61496e.protect@whoisguard.com)
   +1.6613102107
   Fax: +1.6613102107
   11400 W. Olympic Blvd. Suite 200
   Los Angeles, CA 90064
   US

Technical Contact:
   WhoisGuard
   WhoisGuard Protected (f1523859958c4c18a48b1813ac61496e.protect@whoisguard.com)
   +1.6613102107
   Fax: +1.6613102107
   11400 W. Olympic Blvd. Suite 200
   Los Angeles, CA 90064
   US

Status: Locked

Name Servers:
   dns1.registrar-servers.com
   dns2.registrar-servers.com
   dns3.registrar-servers.com
   dns4.registrar-servers.com
   dns5.registrar-servers.com

Creation date: 30 Apr 2012 02:30:00
Expiration date: 29 Apr 2013 18:30:00

[...]


text:
Where does change go when making a transaction from funds imported from a paper wallet?
I'm new to bitcoin and have read numerous articles about it, but I still have questions about how it works.
All the articles that I read say the same that, once I spend bitcoin from paper wallet its address gets depleted. So what does that mean exactly? My understanding is that after importing my paper wallet (for example I use it for a donation) to software wallet, the bitcoins still belong to the paper wallet. I didn't transfer them into software wallet address. In other words, I let the software wallet manage my paper wallet, right?
So after I import it, I want to spend it (say I have 2 bitcoins in paper wallet). I want to sent 0.5 of 2.0 bitcoins to, for example, an address belonging to Alice. After that transaction all the paper wallet bitcoins are sent to the network to split into 0.5 and 1.5. 0.5 goes to Alice, and 1.5 goes back to where?
To my software wallet address or paper wallet address (as it was specified as outgoing address)?
If they're going back to the paper wallet, how is that that there're a lot of topics that someone lost all the change after the transaction?

Great to see that you are learning about BTC.
A paper wallet contains all the necessary details which you require to access your BTC.
But the true purpose of a paper wallet is security. Once you create one paper wallet and transfer BTC to the address, unless the person get's the physical paper, there will be no way to steal it by hacking or any other way.
Now coming back to your question, there are two ways how you use a software for your paper wallet.

By importing
In this method, if you transfer your BTC as you say in your question, your paper wallet will remain the rest 1.5 BTC
By sweeping/transfer to software
In this method, your total BTC will be transferred from your paper wallet to software wallet. In this case, after your transaction, the software will contain your remaining amount.

Note: Some software uses change addresses, so even if you use any of the above method, the rest goes into the change address created by that software wallet rather than your paper wallet. This is for privacy concern and mainly depends on the software you choose.
Hope this answers your question.

Related, for the Electrum wallet: https://bitcointalk.org/index.php?topic=2365006.msg24171260


text:
Where is documentation for the CLI for the GameCredits Core for Windows?
I am using GameCredits. I installed the node software locally and synced all the content. However, no helpfile seems to come with the software and I don't know how to start. I am quite new to this world of blockchains.
Could you point please to an official documentation regarding the CLI? I'm somehow struggling with the QT version, but perhaps learning to use the CLI could be useful to build a web interface of my own. I would like to, sooner or later, use it as integrated in a game of my own, but I don't know how to start.


text:
What's the best way for someone in Israel to move money in and out of Mt. Gox and/or Tradehill?
There is an Israeli bitcoin exchange (BitCoil), but it has been closed some time before and it doesn't currently support limit orders. I want to understand what's the best way, without using BitCoil, to move dollars in and out of Mt. Gox and/or TradeHill from an Israeli bank account.
The "best" way would be cheapest, most secure, convenient, fast and reliable.

possible duplicate of How do you obtain bitcoins?

For smaller amounts you could buy bitcoins from another who holds ILS on BitMarket.eu.  http://bitmarket.eu/market/ILS or over the counter on the #bitcoin-otc marketplace: http://www.bitcoin-otc.com
TradeHill had been planning on adding ILS, but there was a setback:
 - http://bitcointalk.org/index.php?topic=19537.msg366806#msg366806
For larger amounts, having your bank send USD funds via an International bank wire to an exchange would likely the cheapest and fastest method even though the fees to do so are sizable.
 - http://en.bitcoin.it/wiki/Buying_bitcoins

TradeHill has international wire transfers and Paxum. They only charge $20 for incoming and outgoing international wire transfers while Paxum costs a dollar a transaction. Funds withdrawn or deposited via wire transfer should be available within a few business days. Paxum should be processed within a few hours (during EST business hours).
More info on deposits and withdrawals.
https://www.tradehill.com/DepositOverview/USD/
https://www.tradehill.com/WithdrawOverview/USD/
Mt. Gox. does not offer withdraws via international wire transfer. They do accept incoming wires which can be sent to their account in Japan.
https://en.bitcoin.it/wiki/MtGox#International_USD

Maybe you could use your ILS to buy in-game currencies like Linden Dollars or WoW Gold which can then exchange freely with BTC


text:
Is there a way to undo transactions with a "too low" fee?
Suppose we reach a state where only transactions that pay a fee are accepted by miners. Further supposed that someone created a transaction using an old/odd client that allowed them not to send any fees.
In this case, what would happen to the transaction? Could it be undone? Would the coins be lost forever?

I have successfully used the methodology described here to delete a transaction which didn't go anywhere because of a too low fee. In short, the process is as follows:

Configure Linux machine with db4.8-util and bitcointools. Ubuntu works fine.
Run following command on your data folder:
./dbdump.py --datadir ~/.bitcoin --wallet-tx > tx.txt

Open tx.txt using text editor. Find transaction in question. Should look like:
==WalletTransaction== 12a75d48a002ab920 ...
block: 00000000000000000000000000000000 ...
2 tx in, 1 out
TxIn: value: 0.007640 prev(c09e92cb94ff1fb6d4 ...
TxIn: value: 0.000050 prev(7dcda75e6ad8b5adc7 ...
TxOut: value: 0.007690 pubkey:  Script: DUP HA...

Reverse the 12a75d48a002ab920... value, get something like 92ab02a0485da712. Don't need to reverse the whole line, just a few hex values from beginning. You will need to search for this in the database dump.
Dump the database using following command:
db4.8_dump ~/.bitcoin/wallet.dat > dumpfile

Using text editor open the dumpfile and search for that 92ab02a0485da712 line you found earlier. There will be two lines - key and value, you need to delete both. Save the file.
Re-import the database using the following command:
db4.8_load ~/.bitcoin/wallet2.dat < dumpfile

If all went fine, the wallet2.dat will have a database without transaction in question.
All of this, of course, only works if transaction was never accepted by the network, which is likely the case if you already waited a day, and nothing happens. There is no way to undo transaction which was already accepted by the network. I tried this technology twice and both times worked fine.

The transaction would have no effect. A transaction that wasn't accepted by the network has no effect on the ability to spend coins. The person whose coins were affected could simply delete that transaction from his own database. There's no need to undo the transaction since it was never committed to the block chain anyway.

But ... the transaction appears in the network immediately. If I transfer from A to B, B sees the TX immediately with 0 confirmations. So how can A delete it?

You're assuming a broken network configuration where transactions are accepted for relaying even though no miners are willing to commit them. There are many ways you can break the network with inconsistent configurations, that's just one of them. Everyone who participates in the Bitcoin system wants a useful system and the network would not be permitted to go into a useless state. (What if all miners refused to include any transactions at all?)

What? I'm assuming someone using an unofficial or old bitcoin client, that doesn't include any TX fees. In this case, his transaction will be seen immediately, but it might take years for his TX to be confirmed, if at all.

Right, I understand that. If the network permitted a transaction to remain pending indefinitely without some way to override it with another transaction, the network as a whole would be broken. A broken client can't cause lost coins, you can just use a different client.

Generally it is assumed that any client at that time will require a fee. As most clients require a fee now unless you start them with the no fee flag.
I suppose anyone could write their own client or use a client that has it re-enabled, but that is really on their own head and their best bet then would be to mine until they get a block and add their transaction to the block. That might take a couple years, but hey, they wanted a free transaction.

So if someone is using such a client, the TX would essentially be lost (except for the "mine your own block" solution)? There is no way to undo it or add fees retroactively, right? Hmm, someone could create a mining pool that includes specific transactions for an increased fee.

More likely a  bank or such would create their own pool to handle their own transactions.. for no fee.


text:
When an attacker publishes a longer chain, does Bitcoin Core emit a warning?
I tried answering a question about a majority-attacker's power to change the blockchain yesterday.
There is one thing I haven't been able to get a clear picture on, yet:
When a previously unknown chain fork of at least 7 blocks length is published, how does Bitcoin Core react?
main.h: CheckForkWarningConditions appears to emit a warning stating "Chain state database corruption likely".
Would Bitcoin Core accept the chain fork if it had the most work? How prominent is the warning to the user? Does Bitcoin Core need manual intervention to decide which fork to accept?

When a previously unknown chain fork of at least 7 blocks length is published, how does Bitcoin Core react?

It reorganizes to that chain, any transactions that were lost are returned to the nodes mempool.

Would Bitcoin Core accept the chain fork if it had the most work?

Any valid chain with the most work will be reorganised to.

How prominent is the warning to the user?

That warning isn't shown to a user in a reorganisation. Users are shown a warning when there is a significantly higher chain than them with valid proof of work but invalid contents, or alternatively when a soft fork takes the block version number higher than their client is aware of. When a warning is shown to a uiser through the alert system, it is either in the alerts field of the RPC output or in a small yellow bar in the GUI client.

Does Bitcoin Core need manual intervention to decide which fork to accept?

The code has the rules, if users made their own decisions about what constituted "valid" the network would fragment. There is no concept of an "evil" chain or an "attacking" chain, only the best chain.


text:
Are Hashed Timelock Contracts and Zero-Knowledge Contingent Payments the same thing?
This answer to How is a node in the middle prohibited from keeping the money in a routed Payment in Lightning network? describes how a Hashed Timelock Contract would be used to exchange the "secret" for a payment. This sounds a lot like the Zero-Knowledge Contingent Payment described by Greg Maxwell.
Would I be correct in assuming that the HTLC would be implemented including a ZKCP?

Not really. Both use OP_CLTV, in order to recover from a situation where one side refuses to participate in the protocol, but other than that, they're pretty different.
ZKCP has a zero knowledge proof communicated outside of the blockchain. On the other hand, HTLC passes signed transactions back and forth to update a channel.


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the bitcoin wallet spendable amount is not updating
the spendable amount is not updating to the watch only amount. this is now going on 3 weeks or longer. I am using bitcoin ver 0.12.1
any ideas??

looks like almost all of my transactions are labeled as (watch only).

Did you specifically add these addresses as watch-only? If all your transactions are labeled as watch-only that sounds like you don't have the private keys in your wallet which would explain why your spendable amount is not updating.

I upgraded computers and had to reload bitcoin. I did add addresses manually. is there a way that I can find my private key to remove the "watch only"??

Definition of Watch-only Adress:
An address or pubkey script stored in the wallet without the corresponding private key, allowing the wallet to watch for outputs but not spend them.
So you should find your private keys in order to spend these adresses

I had to open up the old wallet, wait for the wallet to sync and then I transferred all the coins out from the old wallet to the new wallet.

You should probably edit this to say that this is a workaround.  By transferring the bitcoin from one wallet to another, you didn't import the private keys, you simply spent the bitcoin to yourself.


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Is it possible for the miners to collude to blackmail a single wealthy address?
Imagine if a few miners who together control more than 50% of the network hash power decided to charge higher transaction fees just for addresses containing really large sums.
For example, this address here has 69,471.08443061 BTC:
http://blockchain.info/address/1HQ3Go3ggs8pFnXuHVHRytPCq5fGG8Hbhx
Now the miners could decide to reject any transaction going out of that particular address (no matter how small the amount) unless it included a 25% transaction fee. You could call it extortion.
Question:

Is it "illegal" (see below) under the rules of Bitcoin?
How would the rest of the network detect such a problem (given it involves only one particular address)?
How would such a problem be resolved?

By "illegal" I don't mean the network would reject such behavior, because that it wouldn't, but that it would be rejected by most participants in the Bitcoin economy based on an implied understanding of what's fair and what isn't.
[UPDATE]
OK, let's say the mining cartel publishes their new policy on their website and word goes around.
Also, as an incentive to the rest of the participants in the economy, it is announced that part of the higher transactions fees will be distributed to everyone. This is achieved by setting up a single address (a la SatoshiDice) where you can send any amount and in return you'll receive the same amount plus the bonus. You can only do this once per address, because the program checks that the funds don't cross the same address twice.
You could call this a wealth tax or a "Robin Hood tax."

It's similar to what happened in Cyprus recently, where anyone with more than 100,000 euros had to pay a very heavy tax. The rest of the public played along because they were off the hook. What I describe here is not some sort of tinfoil conspiracy scenario, just trying to figure out what's different about Bitcoin that makes it so special. Wealth redistribution happens all the time and there's nothing in Bitcoin that would seem to prevent it.

As far as I understand, the fee works as "I won't include you in a block I produced unless the fee you pay is higher than...". Now if 60% of the network charged 25% fee, that would mean the transactions from address that doesn't pay that fee would need to be processed through the remaining 40% of the network meaning they would come at 40% the normal speed, but otherwise get unaffected...

I think your update changes the question significantly (probably too much for a SE question), but the answer is still essentially the same. In order for a miner to prevent a specific address from moving their BTC, they must not only decide not to mine the transaction but they must also convince at least 51% (most likely more) of the hashing power to not only not mine the transaction but also to ignore any block that does include that transaction.
First of all, I think that this is highly unlikely. Because:

Any combination of entities with >51% of the hashpower also has a very vested interest in Bitcoin. And deliberately allowing extortion would be against the interests of Bitcoin.

Any combination of entities with >51% of the hashpower has other potential ways of exploiting the network, which are arguably a lot more profitable.

The bribery incentive you list wouldn't really work. There's too much anonymity in the system. If you had an address that would give me back 110% of what I sent it, I would send it some money, launder the results into a new address, send it some more money from that untainted address, send it some more money, rinse and repeat.

Even if the "cartel" has 55% hashpower, there is a 1.8% chance that the minority miners could get six consecutive blocks mined. This may not sound like a lot, but if the extorted party just kept pushing trasactions out there it would only be a matter of a few hours before one of the transactions got six confirmations. So, the cartel would either have to be willing to break long strings of blocks (completely putting the network in jeopardy) or they would have an overwhelming supermajority of the hashpower (>90%).

So, in answer to your subquestions:

Is it illegal? Well Bitcoin doesn't have laws. If you mean, "would the protocol allow it?" Sure. A known weakness of the protocol is that if any entity controls a majority of the hashpower then there are some attacks they can make. Luckily there are some checks on this, notably the above comment: that anyone with a majority of the hashpower also has a lot invested into the health of the network. The deliberate limiting BTC Guild did on itself a few weeks ago shows this in action: the very entities that could obtain 51% hashpower are the ones most interested in making sure that no one obtains 51% hash power.

How would it be detected? In your modified scenario, it would be public knowledge. But even if someone tried to build a silent conspiracy, it would be pretty easy to detect if they went through with their threats: there would be orphaned blocks. And all of the orphaned blocks would share two things in common: they would all contain the extorted address and they would all be mined by minority miners. It would be pretty easy to figure out what is going on. Of course, you couldn't stop someone from secretly making threats, but detecting someone carrying out the threat would be easy.

How could it be resolved? Fundamentally the network is controlled by a majority of the hash power. If a supermajority of the miners decided to block an address, then there is no resolution: the majority rules. In a way, this is a feature. No one with the majority of the hash power would do this indiscriminately: it would jeopardize the network. But if the network determined that a particular address or addresses was a threat to the network, then the miners could band together and defend the network from that threat.

To expand on #3 with an example, say that a child pornographer publicly advertised some kind of service and accepted Bitcoin as payment. If, either out of altruism or media pressure, the majority of the hashpower decided to forbid payments to or from that address it would certainly be possible. (Of course, it would then become address "wack a mole", but there are some ways around that if the network could agree.)
TL;DR: The point being that if the miners collectively agree on something, yes, it is possible to effectively control the network. By design. That includes rolling back to a previous version (such as in the fork of March), preventing a theoretical exploit, or even executing a theoretical ban. But it's unlikely that a coalition would be willing to use that power for extortion. The miners have too much at stake in the health of the network.
Update:
I discovered something to add while researching something else. Satoshi made the commment that if transactions are deliberately being dropped that it could be addressed client side by coding the standard client to ignore blocks that they know are ignoring transactions. It was in a slightly different context in that thread, but the gist remains the same. If a majority of the miners colluded to exclude an address, there are some client side ways of giving favor to the "honest" miners, assuming that a majority of the client nodes were willing to upgrade to a version that protected again this.
UPDATE 2021: (8 years later)
There's been some activity on this Q/A recently that brought it back to my attention. And I wanted to note that this scenario effectively did happen in 2016 for Etherium. Through a weakness in the DAO (decentralized organization) protocol, a huge amount of Ethereum was stolen. The amount stolen was a enough that it effectively jeopardized Etherum's viability.
As a result, a hard fork was proposed. In other words all of the miners colluded to prevent any money from being removed from that account exactly as proposed in this Question. It's actually slightly more complicated and extreme than that: essentially all blocks after the hack were invalidated via collusion between the miners.
Obviously this Question was about Bitcoin, not Ethereum, but it is a real world proof of the answer. Can a coalition of miners "steal" money from an account by locking it down? Absolutely: in the end a coalition of miners with a supermajority can do almost anything. In this case, a supermajority of miners "stole" money out of the DAO account because the funds had been obtained via a protocol bug. Which is exactly why it won't happen in anything but the most extreme circumstances (such as a bug in the protocol, like the Etherium DAO incident) because it wouldn't be in the miners self-interest otherwise.
More info on the Etherium DAO incident here.

"... some more money from that untainted address ..." Isn't it rather easy to tell from the transaction history if an address has already received a bonus? The bonus would be calculated based on the amount minus the taint percentage. "... there is a 1.8% chance ..." What if they refuse to build on that block?

"... deliberately allowing extortion would be against the interests of Bitcoin." Plenty of real world extortion by democratically elected governments, no problem there. "The majority rules. In a way, this is a feature." This. We can't discuss politics here, so I'll leave it at that. Any idea what's the right Bitcoin forum to have a discussion like this?

@Manish its trivial to remove taint with a mixing service.

The taint cannot be removed completely, can it? Especially when everyone rushes to claim their bonus (all ins 100% tainted, all outs 100% tainted). Anyway, I could come with an alternative design; it's a small part of the question. Thanks.

For example, this address here has 69,471.08443061 BTC:

I believe there's another that has 100k BTC.

Imagine if a few miners who together control more than 50% of the network hash power decided to charge higher transaction fees just for addresses containing really large sums.

The problem is that if some other miner who isn't part of your cartel sees the transaction, he'll gladly include it.
However, perhaps you mean that you would also not build on blocks that contained transactions from the offending address.

How would the rest of the network detect such a problem (given it involves only one particular address)?

Given that you don't know who owns that address, you need to declare publicly that you're not confirming transactions from that address unless you get a 25% fee. It's rather difficult to extort someone if you don't tell them your demands.

Is it "illegal"

Collecting together a majority of hashpower is definitely against the spirit of Bitcoin - remember that huge kerfuffle on the forums when BTC Guild got 40% of the network hashpower?

[UPDATED]
Also, as an incentive to the rest of the participants in the economy, it is announced that part of the higher transactions fees will be distributed to everyone.

This is a problem for two reasons:

If you're distributing the funds to everybody weighted by how much they send you, then you're taking this wealth redistribution tax and sending it right back to the wealthy.
If you're doing this by address, well, need I remind you that new addresses are basically free?

I also thought of a new problem. Suppose the guy who has the 69k account has a mining rig. 69k makes a transaction with a 25% fee, but doesn't broadcast it. Instead, he puts it into a block that he mines. If he's got 0.1% of hashpower, then he can get it into the blockchain within a week.

Updated the question: The new policy is published on the mining cartel's website. Also, there's a new wealth distribution scheme, potentially approved by the majority of the Bitcoin network. Check it out. I'm curious to know what happens in such a scenario.

@Manish Updated my response.

Follow-up: (1) "... sending it right back to the wealthy." Taking 25% from some and giving away, say, 0.01% to all, that's how taxation works. It could be more progressive, no comments. (2) "If you're doing this by address...." I think it's easy to check if an address has already received the bonus via its transaction history (even if it's a new address!). See: tainted addresses.

Short answer: No.
Any miner is free to include or exclude any transaction into his next block solution attempt anyway. The incentive to include transactions however, are the collectible fees that come along with the transactions.
That being said, controlling 51% of the the total hash power by a single entity just means, on average they are able to mine 51% of all blocks. To have an effective "extortion", the group must control effectively all hash power, which is extremely unlikely.
So, this transaction will be most likely be mined soon anyway, by another miner that plays nice and happily collects the fee.

This is not entirely correct. A colluding majority of hashrate can choose to not work on top of any block mined by the minority, effectively turning their 51% into 100%.

@PieterWuille You are right, I did not think about this scenario.


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What is taint analysis?
I just came across the term "taint analysis" in a crypto-related conversation.
This came up while discussing "tracking bitcoin transactions" so it's somehow related to that. That's all I know.

The “taint” of a Bitcoin transaction evaluates the association between an address and earlier transaction addresses. The more “‘taint” the stronger the link between the two addresses.
https://bitcoin-class.weebly.com/taint-analysis.html

More specifically, taint analysis can be used to track dirty money across the Bitcoin blockchain. Its theory is however disputed.


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What prevents one from replaying a BCC transaction by nulling the SIGHASH_FORKID bit?
BCC transactions are "replay-protected" by the SIGHASH_FORKID 0x40.
However why can't I take one such transaction, flip off the 0x40 bit and here's a valid transaction on the BTC chain?
I guess that bit enters into the signature somewhere, but where?

First of all the sighashType field with (or without) any bit fields is used in source data while for signing. The signature does not sign itself, but it signs sighashType. So, changing sighashType invalidates signature.
Second, the data for signature is created in different manner.


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What algorithm do bitcoin miners use to choose which tx to include in their block?
I understand it's in the miner's best interest to receive as many fees as possible for his hopefully-accepted block, hence it should include the most rewarding (fee / size) txs - up to the 1MB limit.
However, what algorithm do the miners use? It seems like a knapsack problem, which is NP-Hard, so I doubt miners actually go for the optimal solution.
Thanks!

No. this is not knapsack problem and no one need to find optimal solution.
Sort your transactions in mempool by two rules:

subsequent transactions can not be to the left of parent ones
most profitable transactions (fee/size) gravitate to left

and take leftmost transactions from mempool until 1 mb limit

Great, thanks.
Where can I find the code that implements this behavior?

somewhere in https://github.com/bitcoin/bitcoin (cy, Captain Obvious)

this isnt the full truth, and miners likely differ in their implementations. one way to prove this isnt the full truth is to look at the existence of transactiln accelerators, another to look at blocks with 0 transactions and a third to look at blocks with some transaction types excluded.


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Is it possible to transfer BitCoins from BlockChain to CoinBase?is there any transaction fee invloved?
I am thinking of transferring my bitcoins from BlockChain to CoinBase
is there any transaction fee invloved?

There will be a fee because the transaction will be broadcast and saved to the Bitcoin blockchain. You can probably start the transfer process on Blockchain and they will show you a preview of what they estimate the fee to be. It all depends on the size (in bytes) of the transaction. For more see their explanation about bitcoin fees

Moving bitcoins from one exchange to another requires transacting on the Bitcoin blockchain which is different than the trading fees implemented by exchanges.
The price of the fee depends on the size of the transaction (in bytes), and speed of the transaction confirmation depends on satoshis per byte. The more you pay, the faster confirmation time you can get.
Estimatefee.com is one tool to estimate bitcoin fees.

Guys,right now i'm using blockchain.com but it doesn't provide me with selling or withdrawal, i thought of using coinbase or paxful,any pros cons on those?

Blockchain.com is exclusively a wallet company not an exchange. So you wont be able to sell any bitcoins there. Instead of "sell" or "withdraw" look for "send". Create an account at an exchange like Coinbase  then copy your wallet address there into the send "To:" destination in your blockchain.com account.


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Value of Product Based on Bitcoins
If I chose to accept Bitcoin as a payment for my product, and the price of the bitcoin goes up or down, then technically I am not getting as much for my product in the long run correct?  Because the exchange is based on the dollar as one of the currencies.  So If my product cost's 100.00 and that is a certain percentage of a bitcoin then if the bitcoin say its worth 7100.00 that would be .014 bitcoins.  But if the bitcoin decreased in price say to 5100.00 then that same product would cost .019 bitcoins.  Correct?  How dos the fluctuation in price affect the value of my product in dollars?

It depends how you measure value.
If the price of Bitcoin in USD goes down, then it might be because of a change in the value of USD rather than a change in the value of Bitcoin, so in that case fixing a Bitcoin price for your product may reduce fluctuation.
Realistically, the price of Bitcoin fluctuates more than the value of USD. Also, it usually makes more sense to aim for a particular USD amount for a product rather than a particular Bitcoin amount.
To resolve this, you can setup software to automatically adjust your prices so that the Bitcoin prices for your product are linked to the amount of USD you want. There are existing tools that do this, and they aren't unique to Bitcoin as they are used for fiat currency price conversion too.
When using such a tool, you're still exposed to changes in the value of Bitcoin from the time of a sale until the time you trade your Bitcoin for USD, but again you can setup automated software to manage that; it could be used to sell the Bitcoin for USD as soon as possible after each sale.

Your basic understanding is correct.
Many merchants simply accept that the price of Bitcoin to fiat fluctuates and that they were paid the correct amount of BTC at the time of the transation, however, to circumvent the fluctuations many merchants also opt to have their BTC (or a portion of it) transferred directly to fiat currency upon receipt using merchant payment services like bitpos.me (for Australia). There are many such services available in many countries.

You will always have the 0.001 BTC, whether the price fluctuates or not. By accepting bitcoin, you are 'buying into' the BTC ecosystem, mission statement, network, etc, and therefore (most people in that same space) believe that the price of bitcoin will drastically increase in the future, due to scarcity and deflationary monetary policy.
Therefore, such as the pizza which was sold for 10,000 Bitcoins, in the future you will have a certain number of bitcoins, which may be worth WAY more than you paid.
So in closing, you can use it as a currency, to accept payment, and most people in this situation speculate that the price will go up, and they either use it as a savings account or purchase other material with the bitcoin as well.


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Risk to Bitcoin balance when making Bitcoin Gold transactions
If Bitcoin Gold fails to implement replay protection, will I risk losing my Bitcoin when I make a Bitcoin Gold transaction?
Assuming replay protection is not implemented properly, how can I protect myself?

Possible duplicate of How does Bitcoin Gold implement replay protection?

This question should be left open; the question suggested as a duplicate asks how replay protection is implemented whereas this one is asking about risk and risk-prevention.

Here is an article answering this very question https://bitcointechtalk.com/how-to-protect-against-replay-attacks-7a00bd2fe52f.
Through either careful transaction construction, using timelock supporting wallets, or simply waiting some time for things to be settled, you'll be safe.


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Low fee Electrum wallet transaction disappeared, now when I increase the fee it seems to be rejected as a double spend
Can anyone tell me what is happening with my transactions ...
First I move some small amount and didn't see that fee was set up to low so it was "low fee" after that I've made another one and It get status "parent ....". I've read about fees and all that stuff so only thing I could do is wait, after 24h those two transactions disappeared and my balance went back to what it was before those two transactions.
I thought that they where cancelled so I made another one with higher fee. After that when I've check it at blockchain it had "double spender" tag and in electrum was "unconfirmed". After another 24h once again that transaction disappeared and my balance went back. Today I've tried to move my btc to another wallet .. made transaction with high fee and is still unconfirmed and I'm unable to see it in blockchain. Can anyone tell me what I'm doing wrong? My previous 15 transactions went without any problems ...

I have almost exactly the same issue, did you figured out with it?

I faced a similar issue and found this reddit post quite helpful. I'm not a bitcoin expert but I will write an answer describing what I think is happening, since there are no other answers yet.
When you sent the first low-fee tx, it got propagated fine to the network but remained unconfirmed. When you opened the Electrum wallet a few hours later, this unconfirmed tx disappeared because your electrum wallet connected to a node which removed your tx from the mempool for being below its minimum relay fee.
So you created a second transaction, but while most nodes (including block explorers, miners) saw your transaction, they immediately ejected it out of the mempool for being an attempted double spend.
Only your first tx has any chance of going through. But if it has very low fees it might not be mined and be removed from all mempools after some time (3+ days?). So, you have to wait for the first transaction to be removed from all mempools and then create a new transaction with higher fees.
Any confirmation or correction for the above from an expert would be appreciated..
Here is what electrum documentation proposes for cases of unconfirmed transactions:
If you have made a transaction that is unconfirmed, you can:

Wait for a long time. Eventually, your transaction will either be
confirmed or cancelled. This might take several days.
Increase the    transaction fee. This is only possible for
‘replaceable’    transactions. To create this type of transaction,
you must have    enabled ‘Replace by Fee’ in your preferences, before
sending the    transaction.
Create a ‘Child Pays For Parent’ transaction. A CPFP is    a new
transaction, that pays a high fee in order to compensate for    the
small fee of its parent transaction. It can be done by the
recipient of the funds, or by the sender, if the transaction has a
change output. (Here is a step by step guide for this option: link)


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What percentage of Bitcoins stored in a multi sign address?
I am looking for a statistic of the usage of multi-sig addresses over time.
More concrete: what is the percentage of Bitcoins stored in a multi-sig address over time.

I calculated it here summarized per month:
  month       btc      count
  201201   0.010000      1
  201202   1.150000      5
  201203   0.015000      2

  201209   0.010000      1

  201212 137.737103     46
  201301   9.781411      9
  201302   0.100000      2
  201303 527.570925    724
  201304 385.334698   1137
  201305 300.712263    991
  201306  20.247942     78
  201307   6.251700     13
  201308   0.934915      2
  201309   0.499281     10
  201310   0.233557     45
  201311   0.903894    352
  201312   0.184625    796
  201401   0.187421   1237
  201402   0.546214   4086
  201403   0.573631   4314
  201404   1.406338  12761
  201405   1.019459   9331
  201406  13.324859  11959

I counted all multisig output transactions with valid public keys.

Interesting numbers. Any idea why there is such a huge peak around 201304. And it's also strange that in 201404 there a very much transactions, but no real volume. I assume the non-existent months have 0 btc/counts?

thanks for this numbers. Can you tell me how you calculated them and can you calculate this number: "What percentage of Bitcoins stored in a multi sign address?" From the numbers you came up with it looks like it is way less then 3k Bitcoins in total. That is a extremely small number compared to about 11kk Bitcoins in existence.

very small indeed,   percentagewise that would be close to zero.


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How can we prevent distortion of the bitcoin exchange rate?
Is there anything within the structure of bitcoin exchanges to prevent bitcoin price distortion with multiple accounts controlled by one person?
I have seen stocks with similar levels of liquidity be manipulated in price with about five accounts. Each buying and selling to and from each other, to get the price to the most favorable place so that one account with much more capital can take advantage of the price distortion, and buy or sell into the new optimism (more volume when price is high because of new market participants). You can read great detail about this in SEC emergency injunction orders, as they go after people that do this (after the fact though). Some stock promoters are the main perpetrators.
The advantage with bitcoins is that it is not regulated by the Securities Act, with the transparency about how to do this detailed by judicial remedies against those that were under the jurisdiction of the Securities Act.
Given that there are so many bitcoin exchanges, would anything such as the technical structure of bitcoin, the exchanges or bitcoin specific market forces prevent someone from doing this with a series of trading accounts, especially across the more illiquid exchanges?

I see no point in doing such a thing.

It doesn't work and if you try it, as many have, you will just lose money. You go to all this effort to push the price up, and everyone else can sell at the higher price just as much as you can. You go to all this effort to push the price down, and everyone else can buy at the lower price just as much as you can. You do all the work and you get just a sliver of the benefit.

@DavidSchwartz general such actions would be accompanied with some sort of promotion across various forms of media to influence people's decision, whether optimism or pessimism. This rewards the original agent with increased liquidity to sell into, liquidating their holdings before the other participants know that the promotion has ended

@CQM: Whatever promotion you do, everyone else will see it too. If you push the price up, they can sell too. If you push it down, they can buy too. You gain no special advantage for your effort.

@DavidSchwartz a market with the liquidity and market cap of bitcoin is not nearly as efficient as give it credit for

@CQM: It doesn't really have to be efficient. It just has to have a short-term "natural price" and it has to be harder to push the price away from the natural price than towards it. (The more the market has these characteristics, the harder it is to manipulate it.)

There is no single price for a Bitcoin.  There are prices at various exchange markets at any point in time.
Since some exchanges have no requirement that every account has identity verified then there is no way for the exchange to know an account is controlled by another party.
Today's exchanges have no mechnism to prevent what you describe.

thanks for bringing up the differences in exchanges. MtGox required me to send an ID to verify my identity, still there was no requirement I think for me to just have 1 account

so yeah, this happened :)


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Selling bitcoin for IDR
I bought bitcoins but my currency is in Rands but I want to sell it to IDR is it possible to do so

please be a bit more specific for others to be able to answer this question, and show what you have tried before. From your question I could guess, that you have South Africa Rand, but honestly I don't know what IDR is. And: you would probably look at an exchange in both countries, so you can get in and out...

Yes you can use localbitcoins and find your country/city and sell it there. Becareful when selling in person. Always meetup in a public space like starbucks, bank, or police station.


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Accidentally transferred Bitcoin to Bittrex Bitcoin Cash account
I accidentally transferred the money from coinbase BTC account To Bittrex BCH account.  It has yet to show up in either accounts.  Can someone help?

I realise the question is a few months old, and no response from OP, so maybe resolved.
But to answer the question for anyone stumbling across this in future, there's a good chance the coins can be recovered for now, but it depends on the address used.  If it's a "1" address, then the private key can be used by both bitcoin cash and bitcoin.  It's likely a manual task for the support team though, so unlikely they will be too happy about this!
Sending to a "3" address may be different, if it's a plain old multisig it could be recovered (I believe, as that's not been tampered with), but if it's a SegWit address, it may be recoverable - for anyone!  Bitcoin cash has no concept of SegWit, so the coins really are "anyone can spend", and in fact someone did claim them all at one point (not sure on the ethics/legality of that one, but that's another topic).
Immediately after the release of the bitcoin cash fork, all bitcoin addresses were valid on the new chain.  The good news is bitcoin cash is switching to a new address type see this question, so should cut down on the amount of issues this will cause in future.

If you have sent BTC to a BCH address your coins are lost.
BCH is not bitcoin it is an altcoin with it's own blockchain, it has been deliberately created by its creators to deceive people into thinking it is bitcoin.

The coins must be somewhere? They can't just be in a dead state / lost? Should there not be an alert on the exchange if someone were to move BTC to BCH?

The answer is incorrect, the coins are recoverable so as long as the service is happy to assist with the recovery. You will need to contact Bittrex for help.

You're wrong. The same private key can be used in both chains for that address.


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What are the arguments for and against using the Lightning Network with Bitcoin?
In addition to the question in the title, when will Lightning Network go online, or, if there isn't a proposed date yet, what is a ballpark indication of when it might go online?

pros:

Lower Transactions Fees
More Transactions per second / block possible
micropayments possible
payments are more private than on bitcoin

cons:

funds are on a hot wallet
(at least currently) node needs to be online all the time
still somewhat buggy
(at least currently) only small amounts can be routed