RPC command to sign text with wallet private key

[gavinandresen]

I'm imagining an RPC call something like:

signtext <bitcoinaddress> "MESSAGE..."
... returns signature, in some standards-compliant format, assuming bitcoinaddress corresponds to a public key in our wallet.

There should also be:
verify <bitcoinaddress> "MESSAGE" "SIGNATURE"
... which return true or false or "I have no idea what the public key for <bitcoinaddress> is".

[jhyslop]

I disagree with this. Bitcoin keys should be used for one purpose only - creating bitcoins. Any other use will erode the anonymity that the system can afford.

Sounds like what you really want is GPG.

[gavinandresen]

I don't see how this erodes anonymity if you don't use it.

And being able to prove that you own a given bitcoin address can be used for all sorts of interesting things for cases where you specifically do NOT want to be anonymous.

[jhyslop]

OK, I'll go along with that.

[jhyslop]

I've been thinking about this some more. Rather than sign an arbitrary message (which is generally frowned on by those smarter than me at cryptography; as I recall, a carefully-crafted message can make it easier to perform certain types of known-plaintext attacks)... um, where was I? Oh, yeah, what about adding specific RPC commands to issue a specific message? For example, if you want to prove you own(ed) a particular coin, you could issue a command something like "getproofofownership

". Of course, under the hood that would be implemented using a routine that signs a message string, but the contents of the message string would be under the program's control.

That would also force us to think through the specific use-cases for which this feature is needed.

[JonnyLatte]

What if you created a temporary key, signed the message with that and then signed the signature or the address of the temp key with your main key. Would this be more secure?