Block explorer verification

[icedevml]

Dear Maintainers,

currently it is required to have an access to a Bitcoin node in order to be able to use ots verify command.

I think it would be pretty straightforward to implement alternative verification method with the support of block explorer API. For instance blockstream.info has a public API with an open access.

Would you accept a pull request if I would contribute block explorer verification support to the ots client? I think it could make this project much more user friendly. It would be possible to use ots verify with a very little effort to setup everything.

[petertodd]

I can't seem to find it right now. But on the ots-dev mailing list (or maybe bitcoin-dev?) there should be discussion of a proposed block header validation scheme specific to timestamps. tl;dr: by checking that a timestamp is committed to by a bunch of Bitcoin block headers, we can prove the total $ value that would have needed to be spent to fake the timestamp. That's not as secure as Bitcoin. But in conjunction with a semi-trusted block header source I think that'd be ok.

Due to security I'm dubious about just trusting third parties like blockstream.info blindly.

[petertodd]

CC: @RCasatta

[RCasatta]

It would work roughly work like this:

ots verify proof.ots

• if bitcoin is running use it
• if it's not running do light verification

light verification

proof.ots attestation attests block is number X

• query block explorer for block header X, X+1,... X+Y
• verify X+Y previous block hash = hash(X+Y-1), repeat up to X
• verify difficulty rules are respected
• tell the user the attestation is committed by Y blocks