Fixed error message in crypto verifier. 
Fixed error message in crypto verifier. 

The error message indicated the type being checked was a private key, but in reality we are checking a public key. (#1672)
Martin2112/trillian,gdbelvin/trillian,RJPercival/trillian,gdbelvin/trillian,AlCutter/trillian,AlCutter/trillian,google/trillian,Martin2112/trillian,google/trillian,RJPercival/trillian,Martin2112/trillian,gdbelvin/trillian