Verifying a signed message *without* a Bitcoin client installed?

[themgp]

If I have a Bitcoin address and a message signed with the private key of that address, is there a way to verify the signature with standard Unix commands?

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[jackjack]

Is a python script (no dependency) ok to use?

[themgp]

Is a python script (no dependency) ok to use?

Yeah, i'm actually looking to do it in Ruby, but i'm guessing i can convert what is thrown at me to my language of choice.

[jackjack]

This is the Bitcoin signature/verification module I made for Armory:
https://github.com/jackjack-jj/jasvet/blob/master/jasvet.py

The function you're looking for is verify_message_Bitcoin(address, signature, message), line 387
Example:

• address: 13C5HZKutjMDeuc7f5mPj6XGpJCZu7xKh2
• signature: H55JIuwEi4YXzINOzx2oU6VsfBcTOScpFtp10pP/M4EWV336ClH65SObwPXnRf/fMXDu8hs8nweB42CtpWgngeM=
• message: aaa

Feel free to ask me anything that isn't clear

[themgp]

From a fairly quick skim through the code, it looks pretty straight forward as written (hahah, though a little more complex than I was hoping!).  The rest of my weekend might be making a Ruby Gem for this.

Do you have tests for this?  I'd love to duplicate some of the tests also.

[themgp]

Just noticed some tests at the bottom: https://github.com/jackjack-jj/jasvet/blob/master/jasvet.py#L551-L579

[themgp]

I released a Ruby Gem to verify signatures. More information:

https://github.com/michaelgpearce/bitcoin-cigs

https://bitcointalk.org/index.php?topic=223426

[Raoul Duke]

Any kind sould will do it in php? 

[piotr_n]

You can also have a look at a tool called versigmsg, from my gocoin project.
https://github.com/piotrnar/gocoin/blob/master/tools/versigmsg.go

If you build it, it end up as a single executable, about 2MB big.

[themgp]

Any kind sould will do it in php? 

Put up a bounty.

[scintill]

I made a standalone C++ tool based on stripped-down bitcoin reference source.  Just depends on OpenSSL.  It should be easy to integrate into any language that can spawn another process and receive its return code, although a native library would probably be better if that's available to you.  https://github.com/scintill/bitcoin-signature-tools

I just added a php demo: https://github.com/scintill/bitcoin-signature-tools/blob/master/tests/verifymessage.php

I would do it in native PHP (a bignum extension required) with this ECC library for a bounty if anyone's interested.

[Raoul Duke]

I would do it in native PHP (a bignum extension required) with this ECC library for a bounty if anyone's interested.

I'll contribute 0.5 BTC for said bounty.

[themgp]

We could also use a JavaScript library while everyone is at it.

[serp]

We could also use a JavaScript library while everyone is at it.

This is covered by https://github.com/bitcoinjs/bitcoinjs-lib

[themgp]

We could also use a JavaScript library while everyone is at it.

This is covered by https://github.com/bitcoinjs/bitcoinjs-lib

Perfect.

[akabmikua]

We could also use a JavaScript library while everyone is at it.

This is covered by https://github.com/bitcoinjs/bitcoinjs-lib

Perfect.

Ok with JS? Why not try http://brainwallet.org/#verify

It works offline and is pretty good.

[serp]

Ok with JS? Why not try http://brainwallet.org/#verify

It works offline and is pretty good.

If you look at the source you will see that the brainwallet you linked uses the bitcoinlib-js linked above.  Using the brainwallet software offline is fine if you are just doing one manually every now and then.  If you are wanting to incorporate the functionality into your own code then it is probably best to use the core library or just write your own.

[scintill]

I'll contribute 0.5 BTC for said bounty.

OK, thanks.  I've got a first draft of some code that isn't working yet (the public-key recovery is a bit tricky), but should have most of what it needs.  So I need to fix the bug, do some test cases, and clean it up.  I'll try to have that done in the next day or so.

[scintill]

I finished the PHP code and put it at https://github.com/scintill/php-bitcoin-signature-routines for those who are interested.

Let me know if you find any problems or have questions.

[scintill]

I've been asked by someone in newbie jail, or unable to register, to post here this online signature verification tool he created: coinig.com.  (Some CYA: this is not an endorsement of the correct functionality, security, privacy, etc. of the tool, just sharing a link.)