I just realize that if we have OP_CAT, OP_CHECKPRIVATEKEYVERIFY (aka OP_CHECKPRIVPUBPAIR) is not needed (and is probably better for privacy)
Bob has the prikey-x for pubkey-x. Alice and Bob will agree to a random secret nonce, k. They calculate r, in the same way as signing a transaction. The script is: SIZE <r-length + 1> ADD <0x30> SWAP CAT <0x02|r-length|r> CAT SWAP CAT <pubkey-x> CECHKSIGVERIFY <Bob pubkey hash> CHECKSIG To redeem, Bob has to provide: <Bob sig> <0x02|s-length|s|sighashtype> With k, s and sighash, Alice (and only Alice) can recover the prikey-x with the well-known k-reuse exploit ( https://en.wikipedia.org/wiki/Elliptic_Curve_Digital_Signature_Algorithm ) The script will be much cleaner if we remove the DER encoding in the next generation of CHECKSIG The benefit is prikey-x remains a secret among Alice and Bob. If they don’t mind exposing the prikey-x, they could use r = x coordinate of pubkey-x, which means k = prikey-x (https://bitcointalk.org/index.php?topic=291092.0) This would reduce the witness size a little bit as a DUP may be used From: bitcoin-dev-boun...@lists.linuxfoundation.org [mailto:bitcoin-dev-boun...@lists.linuxfoundation.org] On Behalf Of Tier Nolan via bitcoin-dev Sent: Monday, 29 February, 2016 19:53 Cc: Bitcoin Dev <bitcoin-dev@lists.linuxfoundation.org> Subject: Re: [bitcoin-dev] BIP CPRKV: Check private key verify On Mon, Feb 29, 2016 at 10:58 AM, Mats Jerratsch <mat...@gmail.com <mailto:mat...@gmail.com> > wrote: This is actually very useful for LN too, see relevant discussion here http://lists.linuxfoundation.org/pipermail/bitcoin-dev/2015-November/011827.html Is there much demand for trying to code up a patch to the reference client? I did a basic one, but it would need tests etc. added. I think that segregated witness is going to be using up any potential soft-fork slot for the time being anyway.
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