Re: [bitcoin-dev] RFC: BIP 322: Generic Signed Message Format
Greetings, (The quoted proposal is already outdated, and I recommend you check out the up to date formatted version here: https://github.com/kallewoof/bips/blob/bip-generic-signmessage/bip-0322.mediawiki The PR with comments is here: https://github.com/bitcoin/bips/pull/725) A big part of the feedback boils down to conflicts of opinion related to whether or not proofs should be given as transactions or not. I am attempting to write down the pros and cons below, some of which are contradictory/complementary based on multiple people's opinions. Pros of using transaction format: 1. works out of the box with existing HSM:s, some of which may be purposefully built to not be upgradable for security reasons (unless sighash modified; see below) 2. easier to incorporate into existing software 3. forward compatible with bitcoin extensions (e.g. mimblewimble, confidential transactions, etc) 4. HSM:s *should* be blind to whether or not a transaction or a message or proof of funds is being signed (see Con #3) Cons: 1. dangerous if challenger is able to convince prover to sign a message that corresponds to an actual transaction; modifying sighash is suggested, but defeats pro #1 above; can define in tx to have txin as sighash to guarantee invalid on chain 2. unupgraded software are unable to make distinction between message sign and transaction sign 3. if HSM:s do not support it and do not support upgrading, this is by design, and message signing should be explicitly supported or not be possible (see Pro #4) 4. severely cripples UX for hardware wallets that actually show the contents of the transaction during the signing If anyone has comments on this, it would be tremendously appreciated. There is also a divided opinion on whether an "OP_MESSAGEONLY" opcode should be introduced, but I'd like to address the above first, if possible. On Tue, Sep 11, 2018 at 1:41 PM Karl-Johan Alm wrote: > > Hi. > > [note: BIP number was assigned to PR before this email was sent; I did > not self-assign the BIP number] > > Below is a proposal to extend the existing sign/verifymessage format > to a more generalized variant relying on the script verification > mechanism in Bitcoin itself for message signing/verification, based on > the original discussion > (https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2018-March/015818.html) > . > > PR is here: https://github.com/bitcoin/bips/pull/725 > > A formatted version of this text can be seen here: > https://github.com/kallewoof/bips/blob/bip-generic-signmessage/bip-generic-signmessage.mediawiki > > Note: I am not sure how to best deal with CLTV/CSV stuff here, ultimately. > > Note 2: I have received suggestions from several people to use a > Bitcoin transaction instead. If someone could explain why this is > beneficial, it would be very helpful. I'm not against it, just feels > like the whole transaction part is unnecessary complexity/overhead. > > --- > > BIP: 322 > Layer: Applications > Title: Generic Signed Message Format > Author: Karl-Johan Alm > Comments-Summary: No comments yet. > Comments-URI: https://github.com/bitcoin/bips/wiki/Comments:BIP-0322 > Status: Draft > Type: Standards Track > Created: 2018-09-10 > License: CC0-1.0 > > > == Abstract == > > A standard for interoperable generic signed messages based on the > Bitcoin Script format. > > == Motivation == > > The current message signing standard only works for P2PKH (1...) > addresses. By extending it to use a Bitcoin Script based approach, it > could be made more generic without causing a too big burden on > implementers, who most likely have access to Bitcoin Script > interpreters already. > > == Specification == > > A new structure SignatureProof is added, which is a > simple serializable scriptSig & witnessProgram container. > > Two actions "Sign" and "Verify" are defined. > > === SignatureProof container === > > {|class="wikitable" style="text-align: center;" > |- > !Type > !Length > !Name > !Comment > |- > |Uint32||4||flags||standard flags (1-to-1 with standard flags in Bitcoin Core) > |- > |VarInt||1-8||msglen||Number of bytes in message string, excluding NUL > termination > |- > |Char*||[msglen]||msg||The message being signed for all subjects, > excluding NUL termination > |- > |Uint8||1||entries||Number of proof entriesWhy support > multiple proofs? In particular with proof of funds, it is > non-trivial to check a large number of individual proofs (one per > UTXO) for duplicates. Software could be written to do so, but it seems > more efficient to build this check into the specification > itself. > |} > > The above is followed by [entries] number of signature entries: > > {|class="wikitable" style="text-align: center;" > |- > !Type > !Length > !Name > !Comment > |- > |VarInt||1-8||scriptsiglen||Number of bytes in scriptSig data > |- > |Uint8*||[scriptsiglen]||scriptsig||ScriptSig data > |- > |VarInt||1-8||witlen||Number of bytes in witness program data > |- > |Uint8*||[witlen]||wit||W
[bitcoin-dev] RFC: BIP 322: Generic Signed Message Format
Hi. [note: BIP number was assigned to PR before this email was sent; I did not self-assign the BIP number] Below is a proposal to extend the existing sign/verifymessage format to a more generalized variant relying on the script verification mechanism in Bitcoin itself for message signing/verification, based on the original discussion (https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2018-March/015818.html) . PR is here: https://github.com/bitcoin/bips/pull/725 A formatted version of this text can be seen here: https://github.com/kallewoof/bips/blob/bip-generic-signmessage/bip-generic-signmessage.mediawiki Note: I am not sure how to best deal with CLTV/CSV stuff here, ultimately. Note 2: I have received suggestions from several people to use a Bitcoin transaction instead. If someone could explain why this is beneficial, it would be very helpful. I'm not against it, just feels like the whole transaction part is unnecessary complexity/overhead. --- BIP: 322 Layer: Applications Title: Generic Signed Message Format Author: Karl-Johan Alm Comments-Summary: No comments yet. Comments-URI: https://github.com/bitcoin/bips/wiki/Comments:BIP-0322 Status: Draft Type: Standards Track Created: 2018-09-10 License: CC0-1.0 == Abstract == A standard for interoperable generic signed messages based on the Bitcoin Script format. == Motivation == The current message signing standard only works for P2PKH (1...) addresses. By extending it to use a Bitcoin Script based approach, it could be made more generic without causing a too big burden on implementers, who most likely have access to Bitcoin Script interpreters already. == Specification == A new structure SignatureProof is added, which is a simple serializable scriptSig & witnessProgram container. Two actions "Sign" and "Verify" are defined. === SignatureProof container === {|class="wikitable" style="text-align: center;" |- !Type !Length !Name !Comment |- |Uint32||4||flags||standard flags (1-to-1 with standard flags in Bitcoin Core) |- |VarInt||1-8||msglen||Number of bytes in message string, excluding NUL termination |- |Char*||[msglen]||msg||The message being signed for all subjects, excluding NUL termination |- |Uint8||1||entries||Number of proof entriesWhy support multiple proofs? In particular with proof of funds, it is non-trivial to check a large number of individual proofs (one per UTXO) for duplicates. Software could be written to do so, but it seems more efficient to build this check into the specification itself. |} The above is followed by [entries] number of signature entries: {|class="wikitable" style="text-align: center;" |- !Type !Length !Name !Comment |- |VarInt||1-8||scriptsiglen||Number of bytes in scriptSig data |- |Uint8*||[scriptsiglen]||scriptsig||ScriptSig data |- |VarInt||1-8||witlen||Number of bytes in witness program data |- |Uint8*||[witlen]||wit||Witness program |} In some cases, the scriptsig may be empty (scriptsiglen=0). === Signing === The "Sign" action takes as input a scriptPubKey and a message (e.g. "hello world"). It succeeds or fails. # FAIL if scriptPubKey already exists in scriptPubKeys set, otherwise insert itWhy track duplicates? Because a 3-entry proof is not proving 3 scriptPubKeys unless they are all distinct, or unless they are proving different UTXO:s (see Future Extensions) # Derive the private key privkey for the scriptPubKey, or FAIL # Define the message pre-image as the sequence "Bitcoin Message:" concatenated with the message, encoded in UTF-8 using Normalization Form Compatibility Decomposition (NFKD) # Let sighash = sha256(sha256(scriptPubKey || pre-image)) # Generate a signature sig with privkey=privkey, sighash=sighash Repeat the above operation for each scriptPubKey, retaining the scriptPubKeys set. As noted, if the same scriptPubKey appears more than once, the sign operation must fail. === Verifying === The "Verify" action takes as input a standard flags value, a scriptPubKey, a message, a script sig, and a witness program. It emits one of INCONCLUSIVE, VALID, INVALID, or ERROR. # Return ERROR if scriptPubKey already exists in scriptPubKeys set, otherwise insert it # If one or more of the standard flags are unknown, return INCONCLUSIVE # Define the message pre-image as the sequence "Bitcoin Message:" concatenated with the message, encoded in UTF-8 using Normalization Form Compatibility Decomposition (NFKD). # Let sighash = sha256(sha256(scriptPubKey || pre-image)) # Verify Script with flags=standard flags, scriptSig=script sig, scriptPubKey=scriptPubKey, witness=witness program, and sighash=sighash # Return VALID if verify succeeds, otherwise return INVALID Repeat the above operation for each scriptPubKey, retaining the scriptPubKeys set. As noted, if the same scriptPubKey appears more than once, the verify operation must fail with an ERROR. * If a verification call returns ERROR or INVALID, return ERROR or INVALID immediately, ignoring as yet unverified entries.