Sign and verify message with bitcoin address and public key #183

Adds two rpc commands :

• signmessage <bitcoinaddress> <message>
• verifymessage <pubkey> <sign> <message>

It allows to sign a message with the public key of a bitcoin address you own, to be sure of the identity of the sender. Command : ./bitcoind signmessage 1L5zqFahc8Ahu9wtgJqCeJMendvD174xsG "Hi github users :p" Output : { "address" : "1L5zqFahc8Ahu9wtgJqCeJMendvD174xsG", "pubkey" : "04ef6e366cd6b0b8fbf02c0c25ad39fe892b90c597875899fdc9db16941cf43fb8c429e0534cb8b972f5cc9f1a50f36dc3352ffad427f073e1c64a145828a3be6e", "sign" : "3046022100a80b6e0c7c54c54ba943f4e3cde12f5a7dc5313e3f0a15ce868f01683ced64fa0221008b4ad7d3800a11c241dcef7aaf44c8224a7d9f1e54d3e669bf4887036b6d10af" }

Command : ./bitcoind verifymessage <above pubkey> <above sign> "Hi github users :p" Output : { "address" : "1L5zqFahc8Ahu9wtgJqCeJMendvD174xsG", "pubkey" : "04ef6e366cd6b0b8fbf02c0c25ad39fe892b90c597875899fdc9db16941cf43fb8c429e0534cb8b972f5cc9f1a50f36dc3352ffad427f073e1c64a145828a3be6e" }

Reviews and comments are welcomed, I don't know if all is used as it should.

Forum thread : http://www.bitcoin.org/smf/index.php?topic=6428.0

EDIT(alex): Sipa's revision references pull 183 - #524

Can you start a forum thread about this? There was some concern about possible attacks revealing private keys if the attacker can send arbitrary data to be signed.

Also some nits: indentation looks messed up on the git diff, and isn't there a better way to get a string into a vector<unsigned char> ?

Forum thread is available here : http://www.bitcoin.org/smf/index.php?topic=6428.0

Can you squash the 4 commits into one please? It'll make the commit history cleaner. (other than that, I agree this is a cool new feature and is ready to be pulled)

ACK, once rebased as Gavin requested

Also: consensus on the forums seems to be that making the padding: address+padding+message ... wouldn't hurt.

Here is the rebased commit plus address used as padding (cool feature the rebase/squash commands :p).

Nice work, khalahan; thanks!

I am not familiar with the JSON RPC protocol, so this may be a silly question: is it necessary for the server to echo some of the parameters back to the caller? (e.g. address when signing and pubkey when verifying.)

$ bitcoind signmessage 1GsDU... hello { "address" : "1GsDU...", "pubkey" : "04c4...", "sign" : "3045..." } $ bitcoind verifymessage 04c4... 3045.... hello { "address" : "1GsDU...", "pubkey" : "04c4..." }

Second question: why not use the address for verifying rather than the pubkey? Can the pubkey not be inferred from the address?

The pubkey can indeed not be inferred from the address. I suggested on the forum to encode the pubkey in the signature output, so the verifymessage interface can take an address. (see http://www.bitcoin.org/smf/index.php?topic=6428.msg108668#msg108668)

amiryal > there is no real need to echo some of the input parameters.

Should i remove duplicates ?

sipa > i replied on the forum

The pubkey can be inferred from the address plus the signature value, however.

I resurrected discussion on forum thread: https://bitcointalk.org/index.php?topic=6428.msg443377#msg443377

Closing, sipa has a more refined version.