text:
Is there a market for converting my foreign currency and coin into bitcoins?
I'm a coin dealer and I have large ammounts of foreign coins (Euro, British Pounds, swiss francs, Japen Yen ect..  I was wondering if I could deposit those coins into my bitcoin account/wallet?

To all would-be downvoters, this is a legitimate question that people unfamiliar to Bitcoin often ask.  DBTN!  (Don't bite the newbs)

Face value or numisatic value?

I think that perhaps you might misunderstand what bitcoin is. If you're looking for a way to sell your physical coins for bitcoin, there are ways to do that. Perhaps bitcoin-otc.com.
If however, you're looking for some way to virtually/digitally trade your physical coins then bitcoin won't help. Depending on what you're actually trying to do, Ripple.com may be the closest digital currency system to help you, see this topic on bitcointalk.org about how one person is leveraging his stash of pre-1964 US silver dimes on Ripple.

I get what you're trying to say here Dave, but it comes across as quite abrupt.

@eMansipater, any better now?

Welcome to the Bitcoin Stack Exchange!  Would it be a fair guess to say you're pretty new to the whole idea of bitcoins?  If so, you've come to the right place!
Let me know if I'm misreading your current level of understanding, but I'll try and get you on track with the whole wallets and currencies thing, because it's a little counterintuitive.  At present the Bitcoin network, which is a completely digital concept, doesn't support the use of tokens equivalent to traditional currencies like euros, swiss francs, or u.s. dollars.  The only token stored digitally in a Bitcoin wallet is a token called the bitcoin, and it's essentially its own currency, except not backed by any country or organisation other than the many people who choose to use it.  It's not a physical object, but a mathematical object kept track of in a secure digital network.  Unlike a service such as PayPal, where your Paypal wallet could hold dollars, euros, or several other types of money at the same time, Bitcoin wallets only hold bitcoins.
The only way that money other than bitcoins can be "deposited" into a Bitcoin wallet is by using it to buy bitcoins from other people, and then depositing those bitcoins into your wallet.  If you've heard about people "putting money into Bitcoin" what they've actually been doing is using their u.s. dollars, euros, or what have you to purchase bitcoins, usually from an online exchange.  Alternatively, you might be able to just find someone in real life who wants to sell you some bitcoins, which is where a website like https://localbitcoins.com would come in.
If your coins have a numismatic value, and you're interested in selling them to someone in exchange for some bitcoins, then you would have to find a willing buyer who will pay you for them in bitcoins (which you could probably do although I don't know specifically where).  There's no way to use the Bitcoin network as a storage or exchange mechanism for your actual physical coins.
Hope that answers your question.  Is it possible that you thought the Bitcoin network was a digital method for people to trade physical coins with?  Because that would be a cool idea too, like a listing service or something.  But unfortunately, not quite what Bitcoin is meant to do.

You would need to find someone to trade with to do that.
Some exchanges may accept cash for some of those currencies, though they probably prefer electronic payments as mailing cash is risky. It's probably a better option to either deposit (and exchange) them at your local bank, and use the resulting funds to purchase your bitcoins.
Alternatively, a person to person trade might work for you. The website https://localbitcoins.com/ might help you with that? (Note: I haven't used it before)

Bitcoin Nordic is a Bitcoin exchange which will accept currency sent to it by mail and use those funds (face value) to buy bitcoins.  They accept GBP, EUR, USD, NOK, SEK, DKK.  They might accept others if you contact them in advance.

http://www.BitcoinNordic.com

I don't know if they would accept much coin.  They might, but possibly not at the discosed rates.  It would be best to contact them in advance.
As far as getting numismatic value for them, you'ld probably get a better offer selling to a numismatic dealer and then using those proceeds with a bitcoin exchange.

Yep there are markets that support the currencies you listed. Do a market search on Bitdango, like this:
http://bitdango.com/markets?quoteCurrencies=EUR,JPY,GBP,CHF&baseCurrencies=BTC
That will show all the markets (exchange + currency pair) that have a base currency of Bitcoin and a quote currency of JPN, EUR, GBP, or CHF. Filter further by exchange, etc.

Just sell your coins on Bitmit (bitcoin ebay) for bitcoin.  I've used that site quite a lot, and think it's excellent.


text:
why wont my hosted (shared) E-Wallet account show my bitcoin balance?
iv transferred 2 bitcoins in to deposit address with a hosted (shared) E-Wallet service.
blockchain clearly shows its there but when im in the E-Wallet service its not showing.
any know what the glitch is? or problem? and also the transaction apparently failed. yet the bitcoins are gone and on the account i wanted them on but there invisible to my E-Wallet service.

Did you try asking the site administrator?

What do you mean by "the transaction apparently failed"? Also, many Bitcoin sites require a large number of confirmations before they acknowledge receipt. Unless you have at least six, I wouldn't worry.

Each hosted (shared) E-Wallet service may function differently.
Most won't give credit to an account until the transaction has confirmed with 6 confirmations.
If your payment has received six confirmations (as shown on Blockchain.info, for example) but still has not been credited to your account, there isn't much you can do other than to open a support ticket with the site or contact the site's administrator.
If the transaction has not received any confirmations, there is nothing the E-Wallet service can do.   If the transaction has received one or more confirmations, just be patient as each successive confirmation is just minutes away.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

sort: votes


text:
What mobile wallet software is available for BlackBerry?
Is there a technical reason why there is no mobile wallet software for BlackBerry users?
Is it just because the marketplace on BlackBerry is awkward? Or are there other technical problems?
Are the Android and iPhone markets easier (less strict) to upload apps to?

I'd guess most wallet software developers first create it for their own phones, and they probably don't use BlackBerry...

Bitcoin is a currency of the future, Blackberry is a mobile OS of the past... unlikely they'll ever meet. And if they do meet, it won't be very nice (fewer and fewer people will be using Blackberry, so an eventual app won't have many users, with everything this implies).

@Lohoris On what exactly do you base those claims? BlackBerry phones have been gaining a higher share of the market in the last few years in the UK.

@SeanChapman: just look with your eyes.

From what I understand (not being a BlackBerry or Android developer, just a small iPhone one), programming for BlackBerry is more tedious and low level than programming for an iPhone or Android. The SDK is less user-friendly, and one has to develop for a lot of screen resolutions (similar to Android, not really so for the iPhone).
All in all, if someone wanted to create an app like that for BlackBerry, there shouldn't be anything stopping them, just that for now there doesn't seem to be anyone wanting to do so. Then again, since there is more and more emphasis on webapps for any smartphone, maybe the need for BlackBerry-specific app is not that urgent.

The Blackberry World (app store) shows two wallet apps:

Bitcoin Wallet by Andreas Schildbach
Bitcoin Spinner (unofficial release, so I'ld check first on the Bitcoin Spinner forum thread to see if it is verified as a straight port with no wallet stealing code injected)]

I have been using Puut Wallet App for my Blackberry device for more than a year. It is easy to use for transactions & payments

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What is the story behind MyBitcoin?
The name of MyBitcoin eWallet comes up quite often here and there. What is the story behind it and the attack on it they claimed occurred?

They had a minimal confirmation count of a single block. This meant that someone could create a bad transaction and confirm it him/herself, that would trick the MyBitcoin software into thinking the transaction was certain (as it has a confirmation). The attacker then transacted Bitcoins away from the MyBitcoin service. When one or two[1] truly legitimate blocks had been created truth would catch the lie, but the Bitcoins were already out of MyBitcoin's reach.
[1] the longest blockchain is considered the valid one. As long as most generation happens on a legitimate chain that chain will become the longest without fail. That means that someone can fake a single block when he's lucky, but a second block building upon that block would be significantly more difficult, as he's now racing with the legitimate blockchain. Assuming the attacker doesn't manage to outrace the legitimate chain his chain will still be one of the longest if the legitimate chain has only a single extra block.
The minimal confirmations used in bitvau.lt is 3. Some services are using even more. It is effectively a security vs. usability tradeoff. The difference in computing power required for generating 3 blocks in a burst is quite significant and would most likely be noticed. If it is not burst-computed it could be would be quite expensive.
Their stoy? They had this error, it got exploited and they decided to give those that claimed it their coins back. In the end a lot of coins were stolen.

Last I heard, victims could apply to get 49% of their bitcoins back, which was the proportion of the site's coins that weren't stolen.


text:
Is there an easy way to search all the transactions?
Is than an easy way to search the list of all bitcoin transactions? For example to find all the bitcoins sent to or from an address?

http://blockchain.info

Try BlockExplorer, it can search by block, public address, and a few other ways. It also has some cool analysis and statistics abilities.

Just remember that a person can have any number of Bitcoin accounts. So if you enter their account and it says their balance is 30 Bitcoins, that means they have at least that many. It can accurately report all Bitcoins transferred to or from a particular address.

http://blockexplorer.com/address/<insert address here>
will give you a list of all transactions to/from that address. Here is an example.


text:
How to Connect bitcoind to one of your workers in a pool?
I'm trying to start using an old tower to mine bitcoin and am slowly trying to make sense of the setup…

Wallet
I signed up for a bitcoin wallet (coinbase) where I am given an id.
Pool
I joined a pool (Slush's Pool) where I verified my email and added my private? id from my wallet.  They registered a first worker for me:
login: myusername.worker1
password: something given

Miner
(my hardware doing maths), Xeon processor

installed ubuntu server 12.04 64-bit
installed bitcoind, sudo apt-get install bitcoind
configured bitcoind, vim ~/.bitcoin/bitcoin.conf
server=1
daemon=1
rpcuser=INVENT_A_UNIQUE_USERNAME
rpcpassword=INVENT_A_UNIQUE_PASSWORD

What I don't understand is how my pool id is ever connected to what's running on my machine?  I also have no idea what to put for my rpcuser and rpcpassword to ensure it is unique.
I've been reading you can't have a period (.) in your rpcuser name?
Not sure what is the minimum needed in this configuration file:

https://en.bitcoin.it/wiki/Running_bitcoind
http://techcrunch.com/2013/04/08/how-to-mine-bitcoins/

I think you are slightly misunderstanding, but you are on a logical path. You need a mining application/program (I suggest BFGminer, if you are on windows then consider guiminer). So what you have is your own bitcoin instance which you could connect to and mine from... And if you some how manage to get a high diff share from that computer possible in a few thousand years you would get a block. (Hence mining in a pool)
A quick tl;dr because it looks like you are using a nix box:

Make sure you have git as well as your general building tools.
Then
git clone https://github.com/luke-jr/bfgminer.git

To compile:
./autogen
./configure --enable-cpumining
make

The “readme” is here: https://github.com/luke-jr/bfgminer/blob/bfgminer/README
Once you have finished making BFGminer, go over to slush pool and
log in. Then, in that right section,is a list of workers under the heading "Workers". It’ll bring you to a page asking you for a login suffix (it is the way to designate each unique computer mining but having it tied to your account) you also are asked to use a password for that miner. I suggest not using your log in password since it is displayed without any encryption on your main log in thread.
Once you entered your login suffix (For example If my username was "Joe" and my computer was called "Feet" (sorry inside joke with some friends have to use it), my suffix would be ".feet". My entire worker name would be "Joe.feet".  My selected password would be "toes" for this example.
After you made a suffix and a password, you click "Save" and you are now back at the main portal. Just again for the sake of repeating. My new worker (also called miner or instance depending on the pool) would be named "Joe.feet" and the password would be "toes"
So "Joe.feet" would be the username I would enter in my mining appplication (BFGMiner). the password would be password I used (in my example "toes").
Now that you have created both a miner and have built BFGminer, figure out if you are on SSE2 or SSE4... once you know which SSE you are using, you can then start mining on slush's pool by using this command (make sure you recurse in to the directory that bfgminer is at). (fyi you could make it a bash script too) (run it in screen as well)
If your on SSE2 run this command other wise i will have the other command a few lines below (again use screen... the command is simply typed screen. You then hit enter twice.)
Make sure you are recursed in to the folder that BFGminer is in and run this code. I am assuming my username on slush pool is "Joe" my worker is called "feet" and my worker password is "toes".
SSE2 version of command
./bfgminer -a sse2_64 -o stratum+tcp://stratum.bitcoin.cz:3333 -u Joe.feet -p toes

SSE4 version of the command
./bfgminer -a sse4_64 -o stratum+tcp://stratum.bitcoin.cz:3333 -u Joe.feet -p toes

After you have done those steps you should see your miner come up to a screen where it says it was connected. At that point you are mining. Please be aware that you have equipment that will probably cost more to run in a day than you will make in profits.

Thank you so much for your help!!!  I looked at my hardware specs via: sudo lshw -html > ~/hardware_info.html and found my cpu has sse2 capabilities.

it looks like your flag -a is to specify the sha256 algorithm type and is only relevant for external hardware (like if i bought one of those specialized dongles).  i just dropped the '-a sse2_64' flag and see something starting to happen.  it looks like it might be waiting for a device or failing to get 'work loads'.  i checked my cpu usage via 'top' and it is very low.  i'm not sure if there is a way to confirm that i'm crunching numbers through my slush account...

yep, looks like no devices are found.  seems to be expecting a bank of erupters...

you compiled with cpu option?
Also try auto detect?
It's one or the other of the below commands. its late so i cant think too well :P
-a fastauto
-a fastauto*
Sorry for taking a while to get back to you.
I'll check back in about 5 hours to see if everything went okay or not.

@e-sushi then there is a miscommunication going on and a misunderstanding. I'll make it a wiki for you to edit as you see fit.

If you're mining in a pool, bitcoind doesn't even have anything to do with the system. It doesn't need to be running, it doesn't even need to exist on your hard drive. The remote pool does that for you.

Assessment
I think you are slightly misunderstanding some things, but basically you are already on the right path.

Wallet
I signed up for a bitcoin wallet (coinbase) where I am given an id.

Great.
When you want to manage your wallet (send and receive Bitcoin, create new wallets etc.) on your local machine, that’s a must. On a side-note: in case you need something easier (meaning: with a GUI), you should take a look at the multitude of desktop clients which bitcoin.org points to; for example: Bitcoin-QT.

Pool
I joined a pool (Slush's Pool) where I verified my email and added my private? id from my wallet. They registered a first worker for me:
login: myusername.worker1
password: something given

That’s perfect.

Miner
(my hardware doing maths), Xeon processor …

Well, you didn’t mention any mining software yet – and that’s where you took the wrong turn.
Filling the gap with Mining Software
Now that you know that your “Miner” needs “Mining software” to be able to actually mine things like Bitcoin, let’s take a look at what you need to start your own mining efforts…
Since you’ve mentioned you’re using the Ubuntu operating system, you could simply dive into the Ubuntu Software Center to download and download one of the ready-build miners:

cgminer
In case you prefer to create your own build from the sourcecode, check the cgminer GitHub repository.
The easier way is to install a ready-made build from the Software Center, or by entering the following commands in a terminal window:
 apt-get update
 sudo apt-get install cgminer

Or you simply install “cgminer” via the Ubuntu Software Center:

bfgminer
In case you prefer to create your own build from the sourcecode, check the bfgminer GitHub repository.
The easier way is to install a ready-made build by entering the following commands in a terminal window:
 apt-get update
 sudo apt-get install bfgminer

Or you simply install “bfgminer” via the Ubuntu Software Center:

You can also create your own build from the sourcecode in case you prefer that. To do so, check the bfgminer GitHub repository.
CPU Miners
Personally, I would not recommend using CPU-only miners because they tend to be slower compared to the above mining software. The reason is simple: CPU miners ignore the potential advantage your GPU (graphic card) might offer. Having said that…
In case you prefer to create your own build from the sourcecode, check the cpuminer GitHub repository.
The easier way is to install a ready-made build by entering the following commands in a terminal window:
 apt-get update
 sudo apt-get install cpuminer

Or you simply install “cpuminer” via the Ubuntu Software Center:

An aside: This mining software project provided the sourcecode-base on which other projects like bfgminer and cgminer were build.

Running the Mining Software
All of the mining software that has been mentioned above comes with dedicated documentation that explains how to compile the software from sourcecode, how to use the compiled software, etc.
But to get you going, I will provide simple examples for both cgminer and bfgminer. I guess you already know how to open a terminal window to start software from a commandline. For the commandline-parameter data, I’m assuming Slush's pool as you indicated in your question, as well as using your example login myusername.worker1 and the example password mypassword.

cgminer
cgminer -o stratum+tcp://stratum.theminingsite.com:3333 -u theusername -p thepassword

bfgminer
bfgminer -o stratum+tcp://stratum.theminingsite.com:3333 -u theusername -p thepassword

cpuminer
cpuminer -o stratum+tcp://stratum.theminingsite.com:3333 -u theusername -p thepassword

Since most command-line parameters will strongly depend on your hardware, you’ll have to read the docs to see if you can tune things towards higher speeds. In case of doubt, --help offers an initial heads-up on potential tuning options of the individual mining software.
That's it… as soon as you’ve got your mining software installed, up and running, you’ll be mining Bitcoin (or alike crypto-currency).
Good Luck – you'll need it
Unless “the Bitcoin fairy” treats you gently, mining Bitcoin using average computer hardware will produce more costs than profits. In the unlikely case you make “profit”, don’t expect hundreds of Bitcoins… rather think in a realistic range of a few Satochi.
Generally, mining is an electricity-vampire. In other words: you can trust in the fact that mining will increase your energy bill. The chance to make profit will depend on a whole lot of luck, and the actual hashing speed you achieve with your mining rig.
If you really want to get your hands dirty and make profit from mining, you’ll have to consider investing in dedicated hardware (ASICs and/or FPGAs) to achieve higher hashing speeds – which can be rather inexpensive, depending on what hashing speeds you want/need/expect. One thing is for sure: the more hashing speed you trying to achieve, the more you'll find yourself buying more and/or better hardware – which will again will increase your energy bill proportionally. and only you can decide where you draw the fine line between “hobby” and “investment”.
In the end, the amount of cash you’ll have to pay for electricity will have the strongest negative impact on your mining efforts and your energy bill will ultimately dictate your break-even point.


text:
Zerocash: how to verify that a mint transaction is correct
I'm reading the whitepaper of zerocash and I don't understand how a mint transaction works. Here are my following questions:
How do you prove that you have enough bitcoins to form a certain amount of zerocoin?
How are the bitcoins locked? What makes you not able to mint bitcoins and using both zerocoins and bitcoins (doubling the value of your bitcoins)?
As an example of the last question, let's say I have 10BTC, I create a zerocoin worth 10BTC, I send it anonymously to Alice, then I make a traditionnal bitcoin transaction of my 10BTC to Bob, what makes this impossible?
If you can't spend the 10BTC anymore (before it has been trasnformed into zerocoin), does that mean we can know how much coin you have minted (eventhough we cannot know how you have spent it)?


text:
What's stopping someone from taking over all the bitcoin addresses?
Anyone can generate unlimited bitcoin addresses.
Presumably, there's a limited number of these (even if it's a very very large number).
What's stopping someone from taking over all the bitcoin addresses? (If the answer is current computer speeds, is it something that's possible in a future 'quantum computer' type era?)

related: Is Each Bitcoin Address Unique?

there's a program called VanityGen that will generate a bitcoin address and private key. You can see the hashing time required grow exponentially with each additional character.

There are about 2^256 private keys, 2^256 public keys, and 2^160 (simple) addresses. There are other addresses (multisig) that have more than one corresponding public key and thus more than one corresponding private key.
2^160 is 1,461,501,637,330,902,918,203,684,832,716,283,019,655,932,542,976.
Just to put that in perspective:
Number of stars in the observable Universe: 2^70
Number of atoms in the Earth: 2^166
Number of atoms in the Milky Way: 2^256
Number of atoms in the known Universe: 2^266

I love this answer.

Number of atoms in the Earth

This is incorrect, no? It's 2^50. https://www.wolframalpha.com/input/?i=difference+between+2%5E50+and+2%5E166

Based on Andrey's 2^160 addresses, I did a thought experiment.
Let's say Dr. Evil wants to occupy all the bitcoin addresses, because of something Satoshi once said about his ears.
He thinks of using 1,000 evil computers for the task, but he's in a hurry and he's quite wealthy, so he buys 1 million evil computers instead.
He sets each of those computers to generate not 1 address per second, but 10,000 addresses per second.
Dr. Evil sets his evil botnet running and sits back in his chair laughing evilly.  But the last laugh is on him.
totalAddresses = 2 ** 160

secondsInOneYear = 60 * 60 * 24 * 365.25

addressesPerSecond = 1000000 * 10000

yearsTaken = totalAddresses / addressesPerSecond / secondsInOneYear

It will take 4.6 x 10^30 years for his bots to occupy all the addresses.
(That is assuming his computers always generate unique addresses.)
If, instead of one Dr. Evil trying to carry out this nefarious plan, one million Dr. Evils coordinate their efforts to reach the same goal, the exponent will fall from 30 to 24.


text:
Why is SHA3 less conducive to ASIC?
Bitcoins are encrypted with SHA-256, and Ethereum is encrypted with SHA3.  Why can miners for SHA-256 encryption guess hashes in the TH/s when miners for the SHA3 encryption can only hash in the MH/s?  Is the algorithm more complex?

Comments are not for extended discussion; this conversation has been moved to chat.

I'm not an expert but I'm a good at digging through academic literature, and this is what I found about SHA3 with relevance to FPGAs and ASICS (and in comparison with SHA2).

Note that this paper dates back from 2011, the winner of SHA3 was not yet decided as NIST only released the SHA3 standard in 2015. Take a look at the Keccak result in this paper. The ASIC space, atleast ASICs with the specific purpose of hashing, have evolved a lot the past 6 years and the numbers are probably not up to date.

These  graphs (and  the  corresponding  tables) have revealed that Keccak is the only candidate that consistently outperforms SHA-2 for all considered FPGA families and two hash function variants (with 256-bit and 512-bit output).

Another paper, which is also pretty old and dates back to 2010 has indications that Keccak (SHA3) is faster than SHA-256.

Figure 5 illustrates how architecture differences affect the performance results. Some curves, like those of Keccak and Luffa, are very steep. This means that a small increase in area yields a significant performance improvement.

Also, I'm not aware of any ASICs for Ethereum, they are currently being mined using GPU's. As you probably already know: GPU's are magnitudes slower than ASICs thus being in MH/s range is no surprise.

Why can't someone make an ASIC with a large memory capacity and a high speed bus?

Your premise is flawed. I think being good for ASIC was one of the reasons why Keccak won: it was both the fastest and had the best performance/area ratio among the finalists for ASIC reference implementation.
By the way, it's easy to see why it is easier to pipeline in hardware if you consider it uses only simple and/xor/rot/not operations, doing away with that nasty 32-bit adder in SHA-2.
While SHA-3 is indeed slower in software, let's not forget that it was designed to not be susceptible to length extension attacks so single SHA-3 can be used in place of Bitcoin's double SHA-2.
References:

http://csrc.nist.gov/groups/ST/hash/sha-3/Round2/Aug2010/documents/papers/SCHAUMONT_SHA3.pdf
https://keccak.team/keccak.noekeon.org/is_sha3_slow.html

By the way, what's the point in ASIC resistance? "Pool resistance" matters a lot more, and that could be achieved by designing the hashing (not the hash!) in a way that no information can be withhold from the miners, maybe as easily as making the full block the subject of the hash instead of just the head.

authors: Алексей Питрович


text:
bitcoind API sendrawtransaction error 500
I'm getting an error 500 from my web server when I try to send a raw transaction through the RPC API.
PHP message:
PHP Warning:  fopen(://...@IP:8332/): failed to open stream: HTTP request failed!
HTTP/1.1 500 Internal Server Error
in /usr/share/nginx/html/common/jsonRPCClient.php on line 132

PHP message:
PHP Fatal error:  Uncaught exception 'Exception' with message
'Unable to connect to://bitcoinrpc:PASSWORD@IP:8332/'
in /usr/share/nginx/html/common/jsonRPCClient.php:140

Stack trace:
#0 /usr/share/nginx/html/tools/do_sendBTC.php(131):
jsonRPCClient->__call('sendrawtransact...', Array)
#1 /usr/share/nginx/html/tools/do_sendBTC.php(131):
jsonRPCClient->sendrawtransaction('010000000115d34...')
#2 {main}

This is the line that crashes:
$result = $bitcoin->sendrawtransaction($tx_data);

Every other API call works, for example validateaddress.
Any idea why this fails? The same raw transaction works if sent through the bitcoind command line.
Thanks

You cannot send one transaction twice. If you have already sent it from bitcoin commandline, then it will fail with -22(cli) or 500(http) error.
500 means incorrect data: insufficient funds, bad syntax, bad type, impossible command...
Try to cast to string: $bitcoin -> sendrawtransaction((string)$tx_data), and do var_dump($tx_data) to find the type.
If it doesn't help, send this POST request from cURL, as in tutorial: https://en.bitcoin.it/wiki/API_reference_(JSON-RPC)#Command_line_.28cURL.29

Using curl I could find out the error. My raw TX had an \n at the end which returned the error 500.


text:
Error: Wallet backup failed! (code -4) when setting up bitcoin-qt for first time
I downloaded and ran bitcoin-qt to play around with.
First thing I did was create a wallet passphrase.
The second thing I did was try to create a wallet backup.
Then I got this message:
Error: Wallet backup failed! (code -4)
If I simply delete the wallet file (no coins on it yet) and then restart bitcoin, everything works fine.  But if I try to encrypt the wallet and then create a backup I get the error again.
What am I missing?
>getinfo
{
"version" : 90300,
"protocolversion" : 70002,
"walletversion" : 60000,
"balance" : 0.00000000,
"blocks" : 340782,
"timeoffset" : -3,
"connections" : 8,
"proxy" : "",
"difficulty" : 41272873894.69702100,
"testnet" : false,
"keypoololdest" : 1422415118,
"keypoolsize" : 101,
"unlocked_until" : 1422419612,
"paytxfee" : 0.00000000,
"relayfee" : 0.00001000,
"errors" : ""
}

>backupwallet wallet.backup
Error: Wallet backup failed! (code -4)

When looking at the debug.log file I see this error:
2015-01-27 16:07:36 error copying wallet.dat to wallet.backup - boost::filesystem::copy_file: Access is denied: "C:\Users\Matthew\AppData\Roaming\Bitcoin\wallet.dat", "wallet.backup"

I've looked at Bitcoin's backupwallet code, and that error is triggered by a filesystem error. I can't tell what kind of filesystem error it is, though. Please open debug.log in the Bitcoin directory. There should be a line like
<date + time> error copying wallet.dat to <path> - <kind of error>

This is the most common type of error:
error copying wallet.dat to <dest> - boost::filesystem::copy_file: Access is denied: "<src>", "wallet.backup"

This means Bitcoin is trying to backup your wallet to C:\Program Files\Bitcoin. You don't have the permissions to backup there. To fix this, run
backupwallet "C:\Users\<username>\AppData\Roaming\Bitcoin\wallet.backup"

instead.

Running both the terminal that is running the "bitcoind" command and the terminal that runs the backup command  with administrator privileges worked for me, saving in the "daemon" default folder.


text:
Bootstrap.dat on Mac OSX 10.9 - Difficulty
Been trawling through a lot of information (I know this similar issue has probably come up a fair bit) on this issue and going round in circles a bit. I am not the most tech savvy individual, and would be really grateful if someone could has some advice that could save me time.
Here is where I am at:

I have a Mac running OSX 10.9.2
I have downloaded and installed the Bitcoin-QT. The synching process was just getting started and I have subsequently quit the application and downloaded the bootstrap.dat file - this torrent is currently downloading via the Deluge application.

Thinking ahead, I have read a bit about where to place this dat file once it has downloaded. For starters, I cannot seem to locate the ~/Library/Application Support/Bitcoin/ on my mac? and I also tried the /Users/username/Library/Application Support/Bitcoin but could not find anything. From selecting the 'Show Package Contents' for the Bitcoin-QT application itself, should I be creating a folder in here manually?
I'd massively grateful for any tips.
John

Since version 0.10 blockchain download speed has been drastically increased and I would advise letting it bring itself up to date rather than trusting and working with a torrent. N.B. Some reports indicate if updating from <0.10 blockchain update crawls but can be fixed by quitting, deleting the old blockchain and starting over. Make sure to backup your wallet.

In the Finder, click the 'Go' menu and choose 'Go to folder' (or just cmd-shift-G)
type
~/Library/Application Support/Bitcoin/

in the field that appears, click go and viola. If you've never previously run bitcoin the directory won't be there but you can go to
~/Library/Application Support/

and create it.
the problem you were having trying to find it if you were using the Terminal to do so may have been that spaces have to be escaped in file paths, so the command to change to that directory would be
cd ~/Library/Application\ Support/Bitcoin

note the backslash before the space. As I've noted you know, you can also drag files or folders in to the Terminal and it will automatically enter the path to that file/folder.


text:
Using Transaction with multiple outputs
Since the output can be spend only once, I am confused by transactions containing multiple recipients. For example, if Alice transfers 5 BTC to Bob and 5 BTC to David in the same transactions. In the future, Bob refers to the Alice's transaction, also David can refer to the same transaction. I understand that outputs are numbered in Alice's transaction to Bob and Eve. Therefore the output number and transaction id Tx id uniquely determines whether there is double spend happening or not.
Am I correct? Is the UTXO associated with output and Tx id?

Near duplicate of http://bitcoin.stackexchange.com/questions/11411/in-getrawtransaction-what-is-the-vout-integer-in-the-vin-list/

Each transaction draws on a set of [1..n] Unspent Transaction Outputs to spend. These we call the inputs of a transaction.
The transaction then assigns the total value of the inputs to [0..n] new Unspent Transaction Outputs. Each UTXO is associated with the creating transaction and uniquely numbered among that set. The most common script that makes up a UTXO is "pay-to-pubkeyhash", where an UTXO can only be spent in combination with a valid signature by it's recipient.
The value of the outputs must be smaller or equal to the value of the inputs. The difference of those two totals can be claimed by the miner as transaction fee.
To come back to your example:
Transaction A1:
Alice -> 5BTC -> Bob (Transaction A1, output 0)
Alice -> 5BTC -> David (Transaction A1, output 1)
(Alice needs to put in at least 10BTC for that transaction.)
Bob wants to spend his money:
Bob -> spend(Transaction A1, output 0, signature) -> new recipient.
Since each UTXO is uniquely identifiable, they cannot both try to access the same UTXO.

Is the UTXO associated with output and Tx id?

Yes, you're exactly right, each UTXO is basically just a tuple (txid, output_index). Then when that output is going to be spent, you refer to it by listing the tuple as an input.
Essentially, that's why they're called "Unspent Transaction Outputs" (UTXOs), not "Unspent Transactions".
For example, look at this random transaction output I pulled of of the block chain:
txid: 564bb87efc20751dde182b678e848ceaa75ac54fd2eab33808842f40e953f7e6
output: 1
scriptPubKey: 76a9148ab215e3d638357551f5e6e7e3384b56bb355a6c88ac

(Note that 1 is the index, meaning it's actually the second output)
Then when the transaction is spent, the input references this previously unspent transaction output.
ID of spending TX: 57149f629790e61a5fbab9e27041858ada6348aa17323c15b9da9659b90717bb
input:
  "txid" : "564bb87efc20751dde182b678e848ceaa75ac54fd2eab33808842f40e953f7e6",
  "vout" : 1,
  "scriptSig": 48304502205b6d49f0e473e5b6134c9ba55dcfdd9e010a226fb29f89e9f4ff1a2b568a1d4c022100af290372ed889ffff948662d7a5b1f2d6eb29dbdcad260ab53f99aba6b6e46e50121020f4db25f5bd35cb2c541ecdbcdb0e7c0be890cb4e25895612f8a1cbb32216ff0


text:
My altcoin bitcoinj fork is failing when trying to compile an Android wallet
I've been sent a bitcoinj fork which is meant to work for the android wallet I'm building. Unfortunately it seems to be causing a failure when tests are run during the wallet compile.
I get the following error message when I try to compile the wallet:
Running com.machadocrypto.kobocoin_android_wallet.util.BluetoothTest
Tests run: 3, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.052 sec - in com.machadocrypto.kobocoin_android_wallet.util.BluetoothTest
Running com.machadocrypto.kobocoin_android_wallet.util.GenericUtilsTest
Tests run: 3, Failures: 3, Errors: 0, Skipped: 0, Time elapsed: 0.039 sec <<< FAILURE! - in com.machadocrypto.kobocoin_android_wallet.util.GenericUtilsTest

formatMKOBOValue(com.machadocrypto.kobocoin_android_wallet.util.GenericUtilsTest)  Time elapsed: 0.032 sec  <<< FAILURE!
org.junit.ComparisonFailure: expected:<[200]0000000000.00> but was:<[35]0000000000.00>
at org.junit.Assert.assertEquals(Assert.java:115)
at org.junit.Assert.assertEquals(Assert.java:144)
at com.machadocrypto.kobocoin_android_wallet.util.GenericUtilsTest.formatMKOBOValue(GenericUtilsTest.java:75)

formatUKOBOValue(com.machadocrypto.kobocoin_android_wallet.util.GenericUtilsTest)  Time elapsed: 0.003 sec  <<< FAILURE!
org.junit.ComparisonFailure: expected:<[200]0000000000000> but was:<[35]0000000000000>
at org.junit.Assert.assertEquals(Assert.java:115)
at org.junit.Assert.assertEquals(Assert.java:144)
at com.machadocrypto.kobocoin_android_wallet.util.GenericUtilsTest.formatUKOBOValue(GenericUtilsTest.java:97)

formatValue(com.machadocrypto.kobocoin_android_wallet.util.GenericUtilsTest)  Time elapsed: 0.003 sec  <<< FAILURE!
org.junit.ComparisonFailure: expected:<[200]0000000.00> but was:<[35]0000000.00>
at org.junit.Assert.assertEquals(Assert.java:115)
at org.junit.Assert.assertEquals(Assert.java:144)
at com.machadocrypto.kobocoin_android_wallet.util.GenericUtilsTest.formatValue(GenericUtilsTest.java:53)

Running com.machadocrypto.kobocoin_android_wallet.util.Base43Test
Tests run: 2, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0 sec - in com.machadocrypto.kobocoin_android_wallet.util.Base43Test
Running com.machadocrypto.kobocoin_android_wallet.util.CryptoTest
Tests run: 5, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 5.254 sec - in com.machadocrypto.kobocoin_android_wallet.util.CryptoTest

Failed tests:
GenericUtilsTest.formatMKOBOValue:75 expected:<[200]0000000000.00> but was:<[35]0000000000.00>
GenericUtilsTest.formatUKOBOValue:97 expected:<[200]0000000000000> but was:<[35]0000000000000>
GenericUtilsTest.formatValue:53 expected:<[200]0000000.00> but was:<[35]0000000.00>

Tests run: 13, Failures: 3, Errors: 0, Skipped: 0

The error is coming from the kobocoinj. I've posted the error message on github
https://github.com/machado-rev/kobocoinj/issues/1
Can anyone give ANY tip on how to move forward from this? I'm just looking for the name of a file to edit that will cause ANY of the numbers in the failure message above to change. Once I'm in the right ball park at least I have something to work with. Right now I'm 99% done but dead in the water.
Any tips or pointers appreciated.

You've changed the MAX_MONEY parameter, so you need to change the tests that depend on it.
This appears to be the offending file.
P.S. Changing MAX_MONEY will not change the maximum number of coins. See: Why doesn't changing MAX_MONEY change the maximum number of coins?


text:
bitcoin files mysteriously show up in trash
I'm usually pretty good at figuring things out, but this one has me stumped. Yesterday I saw 5 or so (don't remember exactly) bitcoin-qt(something).gz files in my trash that i had NOT sent there. It was late and I was tired so left it for the morning. This morning upon starting up, they were gone. I checked through most logs including apt, dmesg, changelog, etc. for clues, but found nothing.
My coins are still in the wallet now and it is encrypted. Should I worry?
Any ideas?
Thanks
Edit:
Maybe there was some update and the files were moved to the trash to be purged upon restart...? I find no evidence of an update yesterday. Maybe I missed something. Bitcoin-qt is in my sources.list. However, I find no such info in the changelog...


text:
Is it possible to buy or send bitcoins without an intermediary?
If I want to buy bitcoins, I can buy them from an online exchange, from an ATM or from another person who has bitcoins. Online exchanges and ATMs charge high premiums because they are intermediaries. If I buy bitcoins from other people, they also charge high premiums. The whole idea behind the blockchain was to get rid of third-parties. Is is possible to connect to the public ledger somehow and acquire bitcoins without a third-party?
I wonder how the first bitcoin transactions were completed when there wasn't any online exchanges, mobile wallets or ATMs. Can programmers somehow connect to the public ledger and do transactions without bitcoin wallets or fees?

Do not mix the fees, and its base. Whenever you transfer amounts of value between two fiat currencies (let's say GBP to Euro), you pay a fee. So if you go from GBP to Bitcoin or from Euro to Bitcoin, you pay a similiar fee to those, who are "in fiat currency" to ramp up.
Now, when you are within the bitcoin ecosystem, and you transfer bitcoins from your account to my account, then you pay a miner fee. Miners make sure, the bitcoin network is working correctly, and this is to be paid.
When you say the whole idea was to get rid of third parties, than you omit the miners. I guess you mean with third parties the "old structures" of the fiat world... They are indeed not required, once you are in bitcoin world.

connect to the public ledger somehow and acquire bitcoins without a
  third-party?

yes, you can setup your own mining equipment, mine some blocks, and get rewarded for it. Otherwise, if you convert Euro/GBP/Dollars, no (see above).

Can programmers somehow connect to the public ledger and do
  transactions without bitcoin wallets or fees?

Yes, with a mining node. No in general. Example: I have my own set of script to transfer bitcoins between wallets. In this sense I can be considered a programmer :-) I assemble a tx, and send it into the network (aka "connect to the public ledger", following specific rules). For the miners to bring my tx into a block, I have to pay a fee.
So there is no such thing as free beers :-)
I consider reading the book "Mastering Bitcoin" from Andreas (http://chimera.labs.oreilly.com/books/1234000001802/index.html) for further info.

I understand the mining concept.
However, this is an extract from Wikipedia
"One of the first supporters, adopters, contributor to bitcoin and receiver of the first bitcoin transaction was programmer Hal Finney. Finney downloaded the bitcoin software the day it was released, and received 10 bitcoins from Nakamoto in the world's first bitcoin transaction."
How did Nakamoto send these first 10 bitcoins to Hal Finney? I don't think there was an online exchange or mycelium wallet to send 10 bitcoins to Finney? That's what confuses me. How did people do transactions in the beginning?

I can't proof it, cause I don't know this history. Given the context and the word "transaction": Satoshi sent the world's first transaction with 10 bitcoins to Hal's bitcoin address. Probably Satoshi had set up before some miners on his PCs, to create/mine blocks, and as such have the Satoshis to send to Hal. Also these miners where required to verify the transaction. So no exchange or whatsoever...

Bitcoins from cash  or real money?

Nope.

I wonder how the first bitcoin transactions were completed when there wasn't any online exchanges, mobile wallets or ATMs

You can generate new Bitcoin using Bitcoin miners ("ASIC") (See What exactly is Mining?). However, you'll need an intermediary to trade your money with an ASIC miner.
If you're an engineer, don't even try to build your own ASIC. You'll lose money due to electricity costs.
When Bitcoin network was released, Bitcoiners used to mine using their computers. That's not profitable anymore.

I like the idea of buying BTC without intermediary!

The simplest way to acquire them without premiums is to get them from the source itself: that is to mine them. This is how first users acquired them.

Next if you buy them directly from a person and they charge more than some figure you think is market value, this is not premium, it's the market value that is higher than what you thought it is.
Note that you must trust that person (that is know him) so you are sure he gives you BTC when you send him dollars.

In reality what you want is to buy BTC from anonymous person online (without trusted intermediary) and you want each of you to be sure you get what you agreed. So this person get's your USD and you get the BTC.
How this would go I'm not really sure, but an idea would be he gives you bitcoins and somehow (through so called smart contract - that is automatic contract enforced by the code) enforces that the bitcoins return to him if he doesn't get the USD within some time limit, and you should unlock them with the key to get them. You acquire that key when you send him the USD. For example you would have a USD transfer site that generates a secret number when you send USD to his account. You would then use this random number (key) that will unlock the locked BTCs giving you control over them.


text:
Need help retrieving bitcoin from an old phone
I recently replaced my iPhone.  A friend tried to erase the old phone to use it for himself but was told it still had a live bank account - I assume my bitcoin account.  How can I retrieve my account and bitcoin?  I still have my old phone but not much else - anything I can do?

An app on your old iPhone could not have prevented it from being erased. It was likely your Apple ID account on the old iPhone that prevented it from being restored. Regarding the bitcoin, which wallet were you using on the old phone? Luckily you still have it, because then you can do a backup and use that backup on the new phone. Also, depending on the wallet, there might be a seed phrase (usually 12 or 24 simple words) that if you possess you will be able to resurrect the wallet on the new phone.

A bitcoin app would not stop your phone from being formatted, so it must be something else.
That said, if you still have bitcoin in a wallet on your old phone, then you should definitely transfer it to a wallet on your new phone (or maybe just recreate your old wallet on your new phone). Just open up the bitcoin wallet, and transfer the funds / export the seed phrase.
Retrieving the bitcoin won't fix your problem of being unable to format the phone, but you should definitely not sell your phone until you have done so!


text:
Recover Bitcoin From Transaction ID
Back in 2013 I bought some bitcoin for a relatively low price, and stored them in an Electrum wallet on my PC. However, I changed PCs a year or two later, and forgot to copy the bitcoin wallet over.
Given the current soaring price, I now have a renewed interest in trying to recover these seemingly lost bitcoins.
I took a screenshot of the blockchain.info page that was displayed shortly after the transaction was completed. I believe this shows the transaction ID, plus the wallet Id it was transferred to.
Here's an edited version of the page I screenshotted, obviously with the IDs hidden so no-one else steals them :)

I've tried revisiting this website, based on the previous URL, which I believe was the transaction Id. I receive an error: Invalid Transaction Hash
Now, obviously bitcoin has split in two, and this was pre-split.
So, what are the various values that are shown on the screenshot (top left appears to be transaction id, bottom right is my wallet id?)
And can any of this be used to rescue the bitcoins?

The ONLY thing you need to recover your coin is the Private Key.  That will (obviously) not be visible on a public website.   You'll have to find your Private Key somewhere on your own harddrive (or paperwallet, or other backup)

@abelenky That's not correct. For deterministic wallets, such as Electrum, the wallet seed can be used to recover the wallet.

I don't remember getting a wallet seed (is that the 10 words it automatically generates for you?) or at least I didn't note one down. I know what the password would be, if that is of any use.
As for private key, no idea. If I ran Electrum on the same PC, would it use the same private key?

All of the information in the screenshot is publicly available.
And no, they won't be useful for recovering your Bitcoin.
If you used Electrum, you either need the wallet, the recovery phrase(seeds) or the private key(s) to recover you Bitcoins. Note that when you first create your wallet, you are instructed to write down the seed (12 or 13 dictionary words), so if you followed the instructions and still have the seed you can recover the wallet.


text:
Pguc coin transfer to address of bitcoin by mistake
I have an account registered with PGUC. In the spend wallet they ask for the exchange address where to transfer the coins. What happened I need to transfer these coins in Pguc address but by mistake I send to Bitcoin address. My coins disappear from the wallet. Can I recover that coin ?

authors: Алексей Плотников


text:
How does the Bitcoin payment forwarding at Blockchain.info work?
We have been using the payment service provided by blockchain.info https://blockchain.info/api/api_receive
It allows us to generate a unique address for each payment and forward Bitcoins received by these addresses to a forwarding address. From what I understand, bc.info pays the transaction fee for the forwarding transaction for us.
We want to use our own wallet. I have two questions:
1) How does bc.info handle this cost? Am I missing something? Are they really paying 0.0001 BTc for each payment their clients receive?
2) Is there a way to forward payments without paying fees?

If the 0.0001 BTC fee is significant for you, chances are you are looking at Bitcoin for micropayments.   Bitcoin wasn't designed for micropayments, and attempting to use it for micropayments will bring angst in the future when even a fee paid incurs significant delays.

WRT 1: The transaction fee comes out of the coins that they forward.

I'm not completely sure how the implementation for Blockchain.info works as I have not tried it myself, but from my understanding what you want is to use a single private key with a corresponding public key that allows you to generate new addresses for every payment you receive, without the need to store more than one private key.
This can be achieved using HD wallets which was introduced with BIP32 that the link you have included refers to.
In simple words this features allows you to take a private key and apply a mathematical function to the private key to generate a new private key (with a corresponding public key and address). This allows you to use the first private key to spend all transactions received to address of the public key of the newly generated private key.
This function can also be applied to extended public keys, and therefore generate a new public key that can be spent using the private key of the public key that the newly generated public key was generated from. This means that you never have to expose the private key to generate new addresses, that it can be used to spend received transactions for.
This might be what Blockchain.info does, which in reality means that they do not forward the payment from the newly generated address. This means that you can receive payments to multiple addresses, without needing to spend fees to use one single private key to spend them.
You can read more about this under the section HD Wallets in chapter 4 in Mastering Bitcoin by Andreas Antonopoulos, or under the section HD Wallet (BIP 32)  in the book Programming The Blockchain in C#, which are both open source and can be found free online.

The fee for each transaction can be calculated using estimatefee API call. And yes, blockchain.info have to incorporate fee in every transaction, 0.0001 BTC being the minimum. One of the reasons attributed for the necessary fee deduction is the quick inclusion of the transaction in the next few blocks.
You can try creating a transaction with the outputs spending all of the inputs and not paying any tx fees. The client will throw an error stating insufficient priority.
Yes you can, but then are conditions apply. You can check out this link to clear things a bit more.

1) I suppose they don't have to pay it, since they receive lot of bitcoins, so it's up to them what bitcoins to choose. Fee depends on transaction amount and time since including an amount in block, so thay can have much old money.
2) Yes. You can wait some time in order to send it without fee (days or weeks), send raw transactions or use modified client from Shadow Of Harbinger

What is the point of the modified client? The github shows no details, except that it is not the latest version and therefor may have issues.

Use Coinbase's "pay with bitcoin" button or iframe. It also generates a new address for each payment but its free and very very simple.

I think this conflicts "we want to use our own wallet" part


text:
Are there any open-source trading bots out there?
Has anyone published an open-source trading bot that runs on a Bitcoin exchange?

Google results contain several such bots.

Instead of commenting each answer I'll write it here. All answers on this page can be improved by adding a little bit of explanation about the software that you're linking to. Answers with just links are not very good answers.

I wrote a simple market maker bot in Python: https://github.com/chrisacheson/liquidbot
This software allows you to place orders on MtGox market.

Liquidbot uses ezl's wrapper code to interface with MtGox: https://github.com/ezl/mtgox

Aricie runs a hosted market maker bot platform: https://dnnbitcoin.aricie.com/default.aspx

ga bitbot
from the project page:

ga-bitbot is a distributed genetic algorithm tuned automated mtgox trading system for Bitcoin which includes market data collection, gene client/server, reporting tools, and automated trading.
The intention of this project is to create a high frequency capable trade platform for the bitcoin p2p currency.

bitcoin arbitrage
From the project page:

bitcoin-arbitrage - opportunity detector and automated trading
  It gets order books from supported exchanges and calculate arbitrage opportunities between each markets. It takes market depth into account.
Currently supported exchanges to get data:
MtGox (USD, EUR)
  Bitstamp (USD, ~EUR)
  Bitcoin24 (EUR)
  Bitfloor (USD)
  Bitcoin-Central (EUR)
  BTC-e (USD, EUR)
  Intersango (EUR)
  Bitfinex (USD)
Currently supported exchanges to automate trade:
MtGox (EUR, USD)
  Bitstamp (USD)
  Bitcoin-Central (EUR) - closed
(under MIT licence)
*TODO:
Tests
  Write documentation
  Add other exchanges:
  icbit
  BitFinex
  Update order books with a WebSocket client for supported exchanges (MtGox, Bitcoin-Central)
  Better history handling for observer "HistoryDumper" (Redis ?)
  Move EUR / USD from a market to an other:
  Coupons
  Ripple ?
  Negative Operations
  use Litecoin or other cryptocurrencies trades

Please add a description, do not post just an URL.

You can try this one also https://github.com/rokj/bitcoin_dealer.
From the README file on the repo:
Bitcoin dealer is simple Django program (trading bot) for trading bitcoins currently only on MtGox exchange.
Bitcoin dealer supports MtGox API version 1 with following currencies: USD, EUR, GBP, PLN, CAD, AUD, CHF, CNY, NZD, RUB, DKK, HKD, SGD, THB, JPY and SEK.
Although program is really simple, it supports stop orders and maybe something more, but I am not really familiar with trading techniques and jargon.
Program is most useful for those who do not have time to watch price of bitcoin all the time, have a PC running all the time and know how to write few "Hello worlds" with two if cases.
Also, the link is not dead at time of editing (21/07/2013).

Welcome here. Please add a description of the software, do not post just an URL.

Link is currently dead, so unless edited this answer is worthless now.

Link is now live again.

When considering a bitcoin trading bot, you must decide where you will trade, generally which exchange you'd like to trade at, such as Binance or Poloniex. From there, you can either use a 'pre-packaged' strategy for buying and selling or developing your own based on various indicators.
I have developed a youtube course where I describe the open source development of a crypto trading bot in python, with all crypto trading bot python code publicly available through github. With this bot you can create and set your own strategies.
Other than my previous description, another well developed crypto trading bot is 'Gekko', open source on NodeJS and can has great, easy functionality to create and implement strategies with large community support.


text:
How do I withdraw bitcoins from my MtGox account?
I've purchased a few bitcoins on MtGox. Now I'd like to spend them. How can I actually spend the coins I purchased on MtGox?
I've looked around mtgox.com for any indication of private keys, bitcoins addresses, hashes etc but didn't see anything. I'm fairly new to Bitcoin so there's probably something fundamental I don't quite understand yet.
Cheers!

Easy: you transfer them to other addresses. Go to Mt Gox, log in, select "Funding Options," select "Withdraw," select "Bitcoin" in the drop down box. You then can put in an amount, and an address of where you want to send your BC (bitcoins).
If you want to know where to spend them, check out https://www.bitcoinstore.com/ as an example. Personally, I am keeping mine as an investment - I have owned them for around 6 months and have made 150% returns. But you can also use them to pay friends around the world without paying a middleman.
Enjoy your cryptocurrency!

Go to funding options -> withdraw funds -> choose withdraw method Bitcoin -> Enter the amount you want to transfer -> Enter a bitcoin adress
Preferably send to your wallet and use your wallet for purchases.

DONT use Mt Gox. You will be forced to provide your passport plus other forms of identification, and then wait at least a month, if ever, (I know it says ten days but that is rubbish( for them to allow you to actually transfer the dollars or bitcoins from your Mt Gox account. I HAVE HEARD STORIES OF IT TAKING ANOTHER MONTH JUST TO DO A TRANSFER. They are completely incompetent.


text:
Easiest way to collect funds of big lists of bitcoin privatekeys
I am setting up an webstore where you can pay with bitcoins. Therefore I created a bulk list on bitcoinaddress.org. I save the public addresses in a database and attach one to each transaction. Then I wait to recieve a notification from bitcoinmonitor.net and complete the transaction.
That will work fine I think, but how can I get the funds from all the different addresses? I know you can import in some software a private key, but it is too much work to do for each order. Do you know something easier to collect the funds of all the generated addresses?

I would import all the private keys into my wallet immediately after generating them with bitaddress.org.  There's no need to wait for them to be used.
See this answer for how to import the whole collection at once.

If you don't want to use your own wallet (and local bitcoind) but instead want to use a hosted solution, you can import all the private keys into Mt. Gox (redeem private key).
Mt. Gox will then sweep any incoming transactions into your Mt. Gox account.  They even have an API for adding (redeeming) these private keys.

The API looks very useful, but I prefer to use my own wallet. Thank you anyway.


text:
With Ripple, how can I move my wallet to/from Payward?
When I created my ripple wallet, I selected local computer.  Now I want to be able to access my wallet from any computer.  How can I move my ripple wallet to the server?
Or suppose I want to remove my wallet from the Ripple server (why would I want to do this?), what is the correct approach?

@Downvoter / Closer: According to meta Ripple questions are on topic .  Please provide constructive feedback for the down vote.

I'm seeking for an authoritative answer for myself, but it seems the answer to the first question is:

On account creation (and whenever you login) you can set the "Fetch
  wallet from" option to one of "Payward", "Payward and Local Browser"
  or "Local Browser".

source


text:
When would I change my Ripple client's Web Socket IP and Blob vault URL?
What are the scenarios (value-add businesses) that would get users to edit the default ripple client and use a custom

Web Socket IP: Port
Blob vault URL

Why even make this a configuration option?  What is the envisioned benefits?  Is this related to a "gateway"?

@Downvoter / Closer: According to meta Ripple questions are on topic .  Please provide constructive feedback for the down vote.

The blob vault URL lets you choose who you trust to hold your wallet. While the wallet is encrypted, the organization that holds your wallet could attempt to brute force your password with the only limits being their computational resources.
The selection of web socket IP and port allows you to choose what Ripple server you want to connect to. The plan is to eventually let you have multiple servers saved in your wallet.
These choices have to do with how your client connects to the Ripple network and finds out your account information and annotations. It is not related to a choice of gateways, what IOUs you wish to hold, and so on.

Hmm, I kind of thought that "the cloud is my blob vault". So currently is https://blobvault.payward.com is taken down, my wallet is gone unless I saved it (in my local browser cache?)

Yes, your wallet would be gone unless you saved it someplace else. Note that this won't cause you to lose your funds -- your funds aren't stored in the wallet. (Make sure your account secret is stored somewhere safe!)

@DavidSchwartz If someone gets my wallet do they automatically have access to my funds, or do they also need the secret key separately?

@Manish: It depends what you mean by "gets my wallet". If you mean they get the wallet file, then no. It's encrypted. If you mean they get the wallet data, then yes. The secret is stored in the wallet. The wallet is encrypted with the user name and password, so someone who somehow got your wallet without knowing the password would find it useless to them. (Unless they were able to brute force the password.)

@DavidSchwartz The username and password is what the Ripple client calls "Wallet name" and "Passphrase"? Is this part of the Ripple protocol, or is this just a client feature (so another client could use a different scheme)?

@Manish: It's just a client feature. Wallets are entirely client side.


text:
What wallets are compatible with Satoshi Dice?
Satoshi Dice requires wallets to be able to receive coins from the same address they are sent.
What are some notable examples that are compatible and incompatible with this?
What are the technical reasons behind such an incompatibility?

BitLotto has the same restrictions and maintains a list of compatible wallets. Currently that list includes:

Bitcoin-Qt/bitcoind (client)
Electrum (client/server)
Armory (client, Bitcoin client dependency)
BitcoinJ (Client)
MultiBit (Simplified payment verification/SPV client)
Blockchain.info (Hybrid EWallet)
Blockchain App for Android, iOS (Mobile app hybrid client)
Strongcoin (Hybrid EWallet)
BitcoinSpinner for Android (Client/server)
Bitcoin Wallet for Android (Simplified payment verification/SPV client)

Essentially everything else is a hosted (shared) EWallet and therefore is not compatible.  This includes EWallets at exchanges, EWallet sites like Instawallet, and other services like mixers and more.

Your link doesn't work....

Satoshi dice uses the same address bitcoins were sent to send them back. There no wallet that does not permit that, how could you spend coins if at first you cannot receive them. The kind of "wallet" satoshi dice is refering to is like you try to spend bitocoin from a broker service (like Mt.Gox) the address they use is not assured to be yours (and the coin will not return back to you)


text:
Can I buy stocks with Bitcoin?
I have got some USD balance with a Bitcoin exchange. I intend to buy stocks for these USDs. Is there an online broker that accepts Bitcoin as a deposit option for stock market trading? I mean the usual stock market where items like Google, Microsoft etc. are traded. Or do I have to go the usual way of withdrawing my USDs from the exchange to my bank account and then invest from there?

I've looked into 1broker and while there is quite a bit of good feedback about the site and the GUI is very clean the 4 guys who run it are students. I ran a hedge fund for many years and know a fair bit about what they do which is CFD trading. The short answer is, and it sucks in a way because eventually they will tank. A black swan event will come along and take them out.
They don't understand hedging (which the main guy says he uses "when he feels it is necessary") That is not hedging. Hedging is a considered and consistent strategy you put in place before you start running your trading business. Not something you do when the mood strikes you. However, it is my belief that eventually a professional group will build a professional platform that supports digital currency as security. The world has to catch up with the idea and i am certain it is coming.
I've got a few BTC I wouldn't mind putting to work. Anyone else?

pyramids provided a really good answer. I would like to add though that as time passes and Bitcoin prevails as an alternative viable virtual currency due to ever growing acceptance/usage then Investment/Financial Firms and Banks may well consider accepting Bitcoin. They would have to remain in business. But you can bet there will likely be BIG FEES for accepting it and stringent margin requirements with minimum 50% in all likelihood and doubtful will allow lending on margin over and above this.

Yes, you can fund a brokerage account with Bitcoin, at least at DriveWealth.
Disclaimer: I have not tried it.
How do I deposit funds?

Last Updated: Aug 11, 2015 05:44PM EDT
  DriveWealth has multiple safe and secure ways to deposit funds into your Live Investing Account:

Charge Cards - We accept Visa, Mastercard, Discover and American Express
Wire Transfer
Check
Dwolla - U.S. Only
TransferWise - For European Currencies
*BitPay*
China Union Pay
Safety Pay - Select Latin American and European countries

How do I deposit funds to my account with Bitpay?

...
  Please Note: Bitpay deposits can take up to 3 business days. When the funds are deposited in your DriveWealth account, you will be notified via e-mail.
There is a minimum $20 deposit. DriveWealth is not responsible for the Bitcoin exchange rates you receive.

No services for mainstream companies, but there are a couple of sites I've seen for stocks and IPO's however these are mostly in Crypto related companies.
https://cryptostocks.com/
https://www.havelockinvestments.com/

You may want to give First Global Credit a try (www.firstglobalcredit.com). They provide stock trading facilities and provide a DMA trading platform (all trades are executed directly on the relevant exchange) with all positions secured using Bitcoin as collateral.
I've tried their simulated trade platform and it seems to do what it says on the tin.

1broker is a brokerage that facilitates Bitcoin purchases of stocks of Google, Microsoft, Apple and Facebook. They also offer Bitcoin investment in commodities and forex.
The service is free to use, as in they don't have an up front charge, but it costs 0.001 BTC per withdrawal. Quoting from their website, "We profit from the spread, the difference between the bid and ask price. This means you will start with a very small loss, when a new position is opened."


text:
What are the key features of eMunie, a crypto-currency that's not a Bitcoin fork?
https://bitcointalk.org/index.php?topic=220530.0
The ANN is not super clear. From what I understand, the supposed key features are:

Immunity to 51% attack
"protection against hoarding" ??? (someone please explain this)
A built-in messaging system

Can someone explain/elaborate?

So whats different
eMunie has similarities to current crypto-currencies by way of a
  public ledger, blocks and transactions.  These however, are where the
  similarities end and innovation for a better system comes into action.
The network is composed of clients, seeders and hatchers, the
  functions of which will be explained in this announcement.  Any node
  can take task in one, or any combination of these roles dependent on
  the users wishes.
The network is resiliant to any type of "51%" attack, as the models
  required to perform such an attack are not present.
Currency generation within the network is a collaborative effort, and
  created currency is distributed according to a set of requirements.
  This distribution should help to ward against hoarding, which can
  further lead to volatility of the currency.
The network performs extensive verification of itself, more so than
  the BitCoin algorithms, to ensure that all participants are honest
  nodes and for additional security overall.
A secure, anonymous peer 2 peer messaging system is built into the
  network, allowing secure, untraceable communications between 2 or more
  parties.

See also https://bitcointalk.org/index.php?topic=220530.msg2666515#msg2666515

Since it's closed source, we can easily dismiss it and we can't definitely answer any question about it anyway.

@Lohoris - didn't even realize it's close source :)

I'm voting to close this question as off-topic because it is about a closed-source cryptocurrency.

What are the key features of eMunie, a crypto-currency that's not a Bitcoin fork?

First off, if the eMunie guys can't provide a compelling answer, then stay away from it.
Second, they are making a lot of bold claims without backing them up.  For example:

immune to 51% problems but transactions are verified by only two hatchers, so it's unclear that is any better..
With eMunie, both hatchers would get a near equal share of that reward - So? Bitcoin already has worker pools which implement the same concept.
The main problem there is that you get a handful of miners with massive hash power - Citation needed. The majority of Bitcoin is mined in pools that payout most of their profits to their workers.   This does not concentrate the wealth.

Regarding Hoarding, from the eMunie forum:
Hoarding will always happen, it's natural for people to keep hold of anything that is of value, but, we have tried to implement measures so that this shouldn't be as extreme as with BitCoin.
The main enforcer of this is of course the distribution method of EMU's, which is a radical step in a different direction than BitCoin and all the other Alt's.
The main problem there is that you get a handful of miners with massive hash power, or a large pool with some miners with large hash power, and they acquire a majority of the BTC created. They hold on to them and supply drops, so the price on the exchanges goes up, to a point where the miners decide now is a good time to cash in, dump those hoarded coins into the market, and the value plummets. Miners are in control of the currency flow within that system, and as always in many systems, you get a few that hold the majority.
With eMunie, the idea is that while 80% of that goes to the hatchers, it is work based, not "first found" based and this alone spreads the allocation around better. For example, a possible and likely common scenario in BTC is of course that one miner finds that block just before you, despite you doing almost the same amount of work, yet they get 100% of the reward. With eMunie, both hatchers would get a near equal share of that reward, thus each of those hatchers can only hoard half as much even with the same amount of work as they would be able to with BTC. Couple that with the fact that a transaction requires at LEAST 2 hatchers to do the same work on it, further spreads that 80% around the hatchers in the system.
That alone should reduce the hoarding by a large percentage and keep the supply spread around more accounts.
The remaining 20% allocation is spread around everyone else with a stake, and while this may seem like that may promote hoarding, that is not the case. The maximum amount of EMU that any one client can recieve in this 20% spread is 1 EMU, no more. In reality, there will be 100's, 1000's even of account with various amounts of EMU held there, so the hourly 12.5 EMU's will be spread very thin, but spread nontheless.
When taken in the context of a thriving eco-system, the fact that 20% is spread everywhere, and quite thinly, and that hatchers are allocated EMU by work and not first found, ensures that the chances of any one account, holding enough EMU to be able to disrupt the market is unlikely.


text:
What client to use for an alternative special purpose blockchain?
Lets say one wanted to create a blockchain for the purposes of providing a scalable back-end for accounting for the trade of some arbitrary unit between people. It would not be a tradeable currency.
A possible requirement for the client would be third party authentication to participate in the blockchain. I'm thinking this because a small niche population could render the blockchain vulnerable to 50% attacks, perhaps there are other ways to prevent this.
Political issues aside, some enhancements have been made to the main trunk code.
Are there any enhancements to the trunk code that are useful for general purpose implementations, or walled garden approaches?

If you don't elaborate what exactly do you plan to do, we can't know what is best for you.
Looks like you are planning to build something that departs in a quite substantial way from Bitcoin, and I'm wondering if relating to it at all does make any sense.

Merged mining is the standard way to bootstrap the hashrate of alternative currencies, if they're similar enough to Bitcoin.

@MeniRosenfeld and it also allows to crush them at no cost (as they usually deserve, btw). Not that they couldn't be crushed anyway by a resourceful opponent.

It's early days so I don't want to go into much detail. It should be enough to say that I would like to use a bitcoin based system as a highly scalable way to keep account of transactions between people, in something that is not a currency.

I've edited the question so it's hopefully more clear now what I'm trying to find out

If all you have is a hammer, everything looks like a nail. - Abraham Maslow

This answer presumes that you need to retain the resilience of a P2P network where there is not a single point of failure.  It also presumes that you need an authoritative source that has the ability to maintain control so that the network is not vulnerable to a 51% attack.
I suppose you could fork the stock bitcoin client without too much effort to create an alt-chain that accomplishes this.
On the fork, add to the block verification a step to also check that each mined block includes a transaction from one of the authorized miners.  The way to tell if the block came from an authorized miner is to have the miner include a spend transaction that comes from a private key assigned to that miner.  (Miners would never broadcast these transactions, so if the transaction appears in a block it would mean only an authorized miner solved that block.)
There are a number of ways the client could learn the list of public addresses for the "authorized miners" list.  This list could be hard-coded into the client even, initially, if needed.
There's the risk of how to handle the situation where an authorized miner ends up compromised or otherwise needs to be removed from the list.
Maybe there's an approach here that kills two birds with one stone.
Have the master node broadcast a heartbeat transaction periodically.  This could be done by having the master mine a block that inserts a chunk of data, similar to how an altcoin that does merged mining works -- it has an exception as to what it considers as a valid proof of work.  In this case, any block that is from the master node is considered as a valid proof of work.  The method to use as proof that the block truly is from the master node is for the block to include a spend transaction from the public address owned by the master node.
That heartbeat from the master could also include a checkpoint hash (e.g., "confirmed by the master authority") -- to limit the damage a compromised miner could do.
Thus the end result is:

Normal nodes cannot mine but will exist as P2P nodes that store blocks and relay transactions.
Miners that are authorized do compete, on a proof-of-work basis.
A master node has power of authority and can intervene (i.e, always has 50%+1 majority) if needed.
Frequent checkpoints from the master can limit the risk from compromized miner nodes.

Only miners who are trusted would mine but even if one of them goes bad, the master can clean up by rewriting all the way back to the last checkpoint.
So it doesn't seem to be too much effort to fork the bitcoin trunk to work in this manner.  Centralized systems are always much easier than decentralized.

How about the genesis block contains payments to 2 addresses.  Any payment from the first address to another turns the owner of the recipient address on as a miner, and any payment from the 2nd address turns the recipient off.  This way the owner of the private keys of the addresses funded by the genesis block has the ability to grant and revoke the ability to mine to arbitrary nodes, given an address the node controls.

Sure, that would probably work.  Could even use the amount as a data fields too -- to notify the "last valid block" that the specific miner was authorized to mine.

Well, I was hoping the amount could be 1 satoshi, or even 0 satoshi (may need to modify the protocol to allow zero-valued payments from the genesis block addresses).  The block that the miner is enabled or disabled from is the block in which the transaction appears...


text:
Is Ripple's trade history recorded?
Currently there isn't a graph of the ripple trade values.
I'd like to know if each trade is recorded in the Ripple's equivalent of the blockchain, so that if in future someone wants to build such graph, it will be able to include old data instead of just newer one.

The ledger chain stores all transactions. So yes, you can rebuild the transaction history.
But the validators don't need to store or serve the whole chain to operate. A new validator only needs the last closed ledger to validate new transactions.
This is different from bitcoin, where nodes need the last output of the relevant public key to validate a new transaction (and that last output won't necessarily be on the last block).
In theory the ledger chain could be forgotten, as validators don't need the history, but probably some "history storage" services ala blockexplorer.com will appear. Some validators can find it useful to store the whole history too.
Since it's not really necessary for the network to work, I'm not sure what happens if a server doesn't serve the ledger history, but I would say the RPC call useful to query the history is this one: https://ripple.com/wiki/RPC_API#ledger_entry


text:
Number of orders at price X in bitcoin exchange's order book
Can I get to know how many orders are placed at a particular price (bid or ask) on an exchange (like Mt.Gox, Bitstamp etc.)? There might be a wall of 1000 BTCs - do I know if this is a single order or 100 smaller orders? I am asking because this has to do something with a stability of an order book... a single big order can be removed quickly and destabilize the market in my opinion.

Why would you care?

Because of security - a single big order can be removed quickly and destabilize the market...

You simply don't know via any existing APIs that I'm aware of. Potentially you could regularly update a market depth API watching for large changes at a price point which would indicate a large order.
However you can't tell whether someone has broken up a large order into a number of smaller orders, and using a bot it's trivial to cancel a large number of orders very quickly.

Google Market Depth, and you'll find plenty of them:
I personally use http://bitcoin.clarkmoody.com/ for MtGox.

I asked about number of orders, not about the order book in general.


text:
Which address do I use to dump private keys from Bitcoin Core wallet?
Trying to get my private keys from bitcoin core wallet
Have got to the part where i put in  dumpprivkey then it wants my address
Which address do i give?

It will be the public address that you want the private key for.
The details available in the question here might be useful:
Using dumpprivkey to make a paper backup


text:
How in the Bitcoin world one prove that a public key is authentic?
I am trying to understand how Bitcoin works, and was wondering how can you prove that a public key is authentic. Here´s what I have in mind to provide more context to my question. Let's suppose I looked at the blockchain and see that Alice has sent a lot of bitcoin in the past. And I want to cause harm to Alice. Let's say that Alice public key is "hjf734hkjf". Then, why I cannot broadcast to the community that the public key "hjf734hkjf" is sending 100 bitcoins to me?

Why did I get a negative vote? An explanation would be helpful.

You are not sending with public key.
You broadcast the transaction message that is signed with private key that only the owner of the coins has. (you can consider signing to be analogous to encrypting in the sense of the question)
Public key that everybody knows can verify this message (verifying can be considered analogous to decrypting here). If the verification is successful it is proven that the message is signed with respective private key that only the owner knows. Therefore it is sure that the owner of coins broadcasted the transaction message.
This process is known as digital signing.

Then, why I cannot broadcast to the community that the public key "hjf734hkjf" is sending 100 bitcoins to me?

That is not how Bitcoin works.
First of all, you do not send from a public key or an address. That idea is related to traditional "accounts", but Bitcoin does not use any sort of accounts system at the protocol level.
When you receive Bitcoin, what is actually happening is that a transaction creates transaction outputs which you are allowed to spend. The vast majority of transaction outputs require that the spending transaction contains a digital signature which corresponds to a specified public key. The digital signature is can only be produced by the private key that corresponds to the public key, so if you do not have the private key, you cannot create the signature that allows you to spend from that transaction output.
So if you see Alice owns the public key "hjf734hkjf" which can spend from transaction outputs with a value of 100 Bitcoin, you can't spend those 100 Bitcoin because you do not have the private key that corresponds to the public key "hjf734hkjf" and cannot create a valid digital signature. Thus any transaction that you do try to create that spends those transaction outputs will be completely invalid and rejected by full nodes and miners.


text:
If ASIC based machines can run at 14TH/s, why isn't the answer found almost immediately?
As far I understand correctly, the objective is to find a nonce which creates a hash with the specified difficulty. The current difficulty being around 1.4 trillion. If that is so, why doesn't a machine which runs at 14 TH/s calculate the nonce in under a second?

The "difficulty" number of 1.4 trillion does not directly correspond to "number of hashes per second".

As explained here in the Bitcoin Wiki, the formula for using the Difficulty to determine the expected time to solve a block is:

time = difficulty * 2**32 / hashrate

Currently, the difficulty is 1,452,839,779,146 so a 14TH/s ASIC miner would be expected to, on average, solve a block with

time = 1,452,839,779,146 * 4,294,967,296 / 14,000,000,000,000

which gives a result of 445707095 seconds, which is about 14 yrs, if I've done my calculations correctly.
To double check that the technique works:
Using the current approx network hashrate (according to blockchain.info) of 10,183,000TH/s, and the same difficulty as indicated above, the formula gives a result of 612s to solve a block, which is the expected result of approx 10 mins.

If it's such a massive number, shouldn't the average nonce be higher? I just took a look at the last block and the nonce was 2075812744. At 14TH/s, that would have been found almost immediately?

The nonce is a 32 bit unsigned integer so the maximum value a nonce can be is 4294967296. However miners do not just increment the nonce; they also do things to transactions within the block to change the merkle root in addition to incrementing the nonce. So there are way more things than just the nonces that they can hash to find a valid block hash.

@DanielGee The person who actually found that block no doubt found the nonce less than a second after they started searching for a nonce to complete that particular block. But miners try very, very large numbers of blocks before they find one that works. Until you find a nonce that works for a block, you have no way to know whether or not one exists. That's why you try every nonce, then start over trying nonces with a different block.


text:
How to sell BCH into BTC
I have an Electrum wallet since Nov 2016 with some BTC.
It seems that I automatically own BCH now (is this right?). What is the simplest way to sell this BCH into BTC?
Should I install a BCH wallet software (Electron?), and initialize it with the same Seed as electrum (isn't this dangerous?)?
Or is there another simpler system to sell my BCH into BTC?

This document issued by Electrum team finally helped a lot:

Users who want to run the Electron Cash binaries should do
  it on a separate machine, that does not have their Bitcoin wallet. We
  recommend to proceed as follows:

Install Electron Cash on a machine that does not have your
  Electrum wallets.
Wait until the BCC hard fork has taken place, and a few BCC blocks
  have been mined.
Move all your Electrum funds to a new Electrum wallet. This will
  move only your BTC, and not your BCC, because the BCC blockchain has
  replay protection. Wait until the transaction is confirmed.
Enter the seed of your (now empty) old wallet or private keys in
  Electron Cash. Since the BTC have been moved to a new wallet,
  entering your old seed in Electron Cash will not put your BTC funds
  at risk.

Following these 4 easy steps you will be able to access your BCC
  without compromising your BTC.

Since you're using a local wallet, read these instructions on obtaining your BCH. For safety, you can transfer all your bitcoins to a new wallet first, then no longer use the old wallet for Bitcoin transactions. Also, installing BCH wallet software on a separate machine is a good idea as otherwise the Electron Cash wallet may sweep the machine for Bitcoin wallets and put your new wallet at risk.
There may be simpler methods, but at this point in time I'd expect they would increase your level of risk substantially.
To sell your BCH for BTC, you'll need to find an exchange you trust that handles both.
If you're interested, there was a fork into "Bitcoin Gold" too, on 24th Oct 2017, though it hasn't gone live just yet.

Thanks for your answer.  transfer all your bitcoins to a new wallet first: will this involve transaction fees?  an exchange you trust that handles both: could you recommend one? (I never know which one to choose)

@Basj on the Bitcoin network, yes, there is a high demand for transactions at the moment compared with the capacity, so you generally have to pay a transaction fee or the transaction won't get processed. https://bitcoinfees.earn.com/ gives an idea of the other transactions currently competing to be processed. I don't have an exchange to recommend, sorry; I haven't done this kind of trade myself yet. I suggest looking for one that has been around for a long time ie more than 3yrs, and trades a high volume.

Step by step process:
Export your private key from Electrum Wallet
Go to Blockchain.info
Sign up and after logging in, go to settings. Then in settings, you will see addresses as shown below:

Then click on Import Bitcoin Address as shown:

Then add your private key as it is in the form as shown:

Click import, and you will be able to use your BTC again.
Transfer your BTC from that address/es to any other new address (just to be sure)
Now to get Bitcoin Cash, just go to Settings > General
There you will see a button near this to claim your Bitcoin Cash as well:

After this, there is an option in Blockchain.info itself to sell your BCH for BTC. Or you can send those to any other exchange out there.
Please follow that and let me know if you were able to retrieve the coins.

Hum, is it really safe to give my private key on an online website?

@Basj No. By using an online wallet you are trusting whoever is managing the wallet. You can split your BCH with a local light wallet. Just be sure to transfer your BTC to a new wallet, as those keys aren't safe to re-use (you will have to expose them to your BCH wallet when you sweep in funds).

@Shadow503 ok so I prefer not to use any web solution. How would you do it (selling the BCH that you automatically have to BTC)?

@Basj I misread your question - I thought you just wanted to split them. In theory, you could craft something called an atomic swap that would allow you to swap cryptos with someone in a trustless manner. Unfortunately, the transactions have to be manually crafted, and the infrastructure for finding a buyer just isn't there. For now, an exchange is necessary for crypto swapping.
Revisiting your original question, as long as you move your BTC out of the wallet containing those private keys first, asterisk's solution has minimal risk. You still have to trust blockchain.info though.

Not sure to understand @Shadow503, could you post a full answer explaining these details? (what do you call "split" them? I just want to sell the BCH into BTC and no longer have BCH).

Basj, please re-read my answer. I have specifically said "Transfer your BTC from that address/es to any other new address (just to be sure)" Even if you don't use a web solution, you need to share your private key with any other software, which may/maynot be compromised. So, I recommend you to transfer your fund before getting BTC and as @Shadow503 said, don't re-use those BTC addresses.

asterisk, so are you saying I should transfer my BTC to another address first (does this involve transaction fee?) with standard Bitcoin (using Electrum). And then I use blockchain.info with the old address, right?

@Basj Exactly. This way you have no way to lose your BTC. As well, you will have total access to your BCH using blockchain.info :)

@asterisk So I have to transfer BTC from my old addresses to new addresses, right? Will this involve fees?

Yes, it will incur normal transfer fees, but that is much better than the risk.


text:
How would debt work in a bitcoin only economy, and why would anyone ever spend?
Been keeping track of BTC for a while and have always had these nagging questions about its feasibility as the "future" of currency. I like all the not tracked, no third party involvement, etc (i.e. all the advantages of having an online currency that should most of the time be safe).
However, in economic terms I have always had a hard time getting my head around how it would feasibly work as the prime currency of a country (to keep it simple).
I guess the closest analogy there exists of such a system is the gold standard right way back when. However, and please correct me if I'm wrong, the issues with the gold standard, principally that when theres no more new gold, theres no more growth, doesn't apply to bitcoin. From posts on this sub and others, it seems that the vision is that when bitcoins stop being made, whenever more money supply is needed, the demand for bitcoin will increase and thus price will as well, thus allowing for a smaller fraction of a bitcoin to be worth more (please tell me if I am understanding this very incorrectly). For example, .01 bitcoins at bitcoin price of 50 dollars isn't much but .01 bitcoins at current bitcoin price is nice.
Thus, in an all bitcoin economy, this sort of argument would imply the price of bitcoin will continue to rise forever, as long as there is growth (i.e more demand for me bitcoins).
So that doesn't really make much sense to me. Growth in this crypto only world doesn't make much sense to me. . The thought experiment that I have been slowly developing but I can't seem to figure out (probably because of lack of bitcoin knowledge and effort) goes as follows:
Say we have gotten to cap of 21,000,000 bitcoins in the crypto-currency only economy (lets contain it to one country). Lets say that 1 bitcoin = 1,000,000 dollars - I know tha it doesn't make sense to compare it to dollars in a crypto only economy - so lets say instead that .001 bitcoins gets you a very very nice high quality TV. So thats the bitcoin relative price context. Now lets say that our crypto economy is doing well, people are working yea yea and are getting hired and productivity is up and so wages are up (woohoo!), so companies have to pay more bitcoins to their workers. -Here is my first confusion in a bitcoin economy-. In our fiat currency economy, when this happens, companies usually borrow money from banks (who were given it by printing money from FED) and they can fund these larger wages and hire-ings and technology advancement (we could obviously discuss the merits of having inflation baked into growth into our current system, but its not really the subject). Question: how is this planned to function in a bitcoin only future???
Is the price of bitcoin suppose to increase here, so that a smaller percentage of the bitcoin, (i.e. 10% of ancient bitcoin price, i.e. .0001) can buy the same tv as before thus in essence having 10x the money supply (in my hypothetical scenario here). If this is the vision, then what are the mechanisms for the increase in bitcoin price? How is the relative price of bitcoin compared to all goods actually increasing (demand by whom?).
Second Question - if what I suppose in the first question is in fact the vision (please correct me if im wrong!), why would anyone ever spend?
If I know that when there's growth, the relative price of my money goes up, I will just never work and wait for growth to drive my bitcoin price up in effect making me richer by sitting there (I may have not understood something really fundamental here cause this really just doesn't work like that does it?).
Essentially this scenario is the one that I've been trying to wrap my head around. I don't expect some full holistic answer to the whole scenario, just want to understand if this is how bitcoin believers envision an economic system based crypto currency behaves, and how they actually envision it. thanks for any input! Also, If I have stated any complete fallacies or falsehoods, let me know, I think it is at least clear what my question is.

Question: how is this planned to function in a bitcoin only future???

They can use their assets as collateral for the loan.
The price of Bitcoin (measured in chicken eggs, for example) doesn't necessarily need to increase when somebody takes out a new loan. The price of fiat doesn't change when people take new loans either.
(If workers become more productive and their pay correspondingly increases, the employer may require more money to fund their working capital, but their cost structure doesn't change - the workers help them earn more and the employer pays them approximately the same percentage of their earnings as before. There it is unlikely that everyone would have to use Bitcoin - if Bitcoin gets used on a large scale, that means multiple crypto-currencies would be in circulation.)

Second Question - if what I suppose in the first question is in fact the vision (please correct me if im wrong!), why would anyone ever spend?

Gold mining generated approximately the same amount of new coins as Bitcoin mining and people would still spend their gold (and silver and stock certificates and diamonds and other savings and assets).
Things worked well before today's fake fiat money existed, and will work equally well after it gets destroyed.
You can learn about it from books and materials discussing how it was before central banks instituted state-sponsored plunder.

Second Question - if what I suppose in the first question is in fact the vision (please correct me if im wrong!), why would anyone ever spend?

Why would anyone spend now? You could buy a nice laptop for $2k today, but if you just invest that into the stock market you can expect to have twice that in around 7 years. The only difference is that the time frame might be smaller if you invest in Bitcoin or other cryptos. Your incentives to spend/save remain more or less the same.