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Diffstat (limited to 'bip-0322.mediawiki')
| -rw-r--r-- | bip-0322.mediawiki | 190 |
1 files changed, 154 insertions, 36 deletions
diff --git a/bip-0322.mediawiki b/bip-0322.mediawiki index 5191143..aaf5496 100644 --- a/bip-0322.mediawiki +++ b/bip-0322.mediawiki @@ -15,6 +15,17 @@ A standard for interoperable generic signed messages based on the Bitcoin Script format. +== Background == + +* Assume two actors, a prover <code>P</code> and a verifier <code>V</code>. +* <code>P</code> wants to prove that they own the private key <code>k</code> associated with a given address <code>A</code> (which in turn is derived from the pubkey <code>kG</code>). +* Let <code>V</code> generate a message <code>M</code> and hand this to <code>P</code>. +* <code>P</code> generates a signature <code>S</code> by signing the message <code>M</code> using <code>k</code>. Given <code>S</code>, <code>V</code> can prove that <code>P</code> has the private key associated with <code>A</code>. + +The astute reader will notice that the above is missing a critical part, namely the pubkey <code>kG</code>, without which the verifier cannot actually verify the message. The current message signing standard solves this via a cryptographic trick, wherein the signature <code>S</code> above is a special "recoverable signature" type. Given the message <code>M</code> and the signature <code>S</code>, it is then possible to recover the pubkey <code>kG</code>. The system thus derives the address for the pubkey <code>kG</code>, and if it does not match <code>A</code>, the proof is deemed invalid. + +While this is a neat trick, it unnecessarily restricts and complicates the message signing mechanism; for instance, it is currently not possible to sign a message for a P2SH address, because there is no pubkey to recover from the resulting signature. + == 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. @@ -23,7 +34,7 @@ The current message signing standard only works for P2PKH (1...) addresses. By e A new structure <code>SignatureProof</code> is added, which is a simple serializable scriptSig & witness container. -Two actions "Sign" and "Verify" are defined along with two *purposes* "SignMessage" and "ProveFunds". +Two actions "Sign" and "Verify" are defined along with one ''purpose'', "SignMessage", with the ability to expand in the future to add a potential "ProveFunds" purpose. === SignatureProof container === @@ -34,13 +45,9 @@ Two actions "Sign" and "Verify" are defined along with two *purposes* "SignMessa !Name !Comment |- -|Uint32||4||flags||standard flags (1-to-1 with standard flags in Bitcoin Core) +|Uint32||4||version||BIP322 version format; must be equal to 1; if > 1, verifier must abort the verification process |- -|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 entries<ref><strong>Why support multiple proofs?</strong> 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.</ref> +|Uint8||1||entries||number of proof entries<ref><strong>Why support multiple proofs?</strong> It is non-trivial to check a large number of individual proofs for duplicates. Software could be written to do so, but it seems more efficient to build this check into the specification itself.</ref> |} The above is followed by [entries] number of signature entries: @@ -56,9 +63,9 @@ The above is followed by [entries] number of signature entries: |- |Uint8*||[scriptsiglen]||scriptsig||ScriptSig data |- -|VarInt||1-8||witlen||Number of bytes in witness data +|VarInt||1-8||witlen||Number of entries in witness stack |- -|Uint8*||[witlen]||wit||Witness +|Uint8[]*||[witlen]||wit||Witness stack, as [witlen] uint8* vectors, each one prepended with a varint of its size |} In some cases, the scriptsig or wit may be empty. If both are empty, the proof is incomplete. @@ -74,42 +81,30 @@ A verification call will return a result code according to the table below. |- |INCOMPLETE||One or several of the given challenges had an empty proof. The prover may need some other entity to complete the proof. |- -|INCONCLUSIVE||One or several of the given proofs used unknown opcodes or the scriptPubKey had an unknown witness version, perhaps due to the verifying node being outdated. +|INCONCLUSIVE||One or several of the given proofs was consensus-valid but policy-invalid. |- |VALID||All proofs were deemed valid. |- |INVALID||One or more of the given proofs were invalid |- -|SPENT||One or more of the claimed UTXO:s has been spent -|- |ERROR||An error was encountered |} == Signing and Verifying == -Let there be an empty set `inputs` which is populated and tested at each call to one of the actions below. +If the challenge consists of a single address and the address is in the P2PKH (legacy) format, sign using the legacy format (further information below). Otherwise continue as stated below. + +Let there be an empty set <code>inputs</code> which is populated and tested at each call to one of the actions below. === Purpose: SignMessage === The "SignMessage" purpose generates a sighash based on a scriptPubKey and a message. It emits a VALID verification result code unless otherwise stated. -# Return INVALID if scriptPubKey already exists in `inputs` set, otherwise insert it<ref><strong>Why track duplicates?</strong> Because a 3-entry proof is not proving 3 inputs unless they are all distinct</ref> -# Define the message pre-image as the sequence "Bitcoin Message:" concatenated with the message, encoded in UTF-8 using Normalization Form Compatibility Decomposition (NFKD) +# Return INVALID if scriptPubKey already exists in <code>inputs</code> set, otherwise insert it<ref><strong>Why track duplicates?</strong> Because a 3-entry proof is not proving 3 entries unless they are all distinct</ref> +# Define the message pre-image as the sequence "Bitcoin Signed Message:\n" concatenated with the message, encoded in UTF-8 using Normalization Form Compatibility Decomposition (NFKD) # Let sighash = sha256(sha256(scriptPubKey || pre-image)) -=== Purpose: ProveFunds === - -The "ProveFunds" purpose generates a sighash and a scriptPubKey from a transaction, an output index, and a message. For multiple simultaneous proofs, it also requires access to the ordered list of proofs. It emits a VALID verification result code unless otherwise stated. - -# Let txid be the transaction ID of the transaction, and vout be the output index corresponding to the index of the output being spent -# Return INVALID if the txid:vout pair already exists in `inputs` set, otherwise insert it -# Return SPENT if the txid/vout is not a valid UTXO according to a Bitcoin node<ref><strong>Synced up or not?</strong> A normal verifier would use a synced up node. An auditor checking records from a client that were submitted in the past want to use a node that is synced up to the block corresponding to the proof, or the proof will fail, even if it may have been valid at the time of creation.</ref> -# Extract scriptPubKey from transaction output -# Define the message pre-image as the concatenation of the following components:<ref><strong>Why not just the UTXO data?</strong> We want the verifier to be able to challenge the prover with a custom message to sign, or anyone can reuse the POF proof for a set of UTXO:s once they have seen it, and the funds have not yet been spent</ref> -#* the string "POF:" -#* the message, encoded in UTF-8 using Normalization Form Compatibility Decomposition (NFKD), including the null terminating character (i.e. write strlen(message) + 1 bytes, for a C string) -#* all transactions being proven for, as binary txid (little endian uint256) followed by index (little endian uint32), each separated by a single `0x00` byte -# Let sighash = sha256(sha256(scriptPubKey || pre-image)) +A private key may be used directly to sign a message. In this case, its P2WPKH bech32 address shall be derived, and used as the input. === Action: Sign === @@ -119,15 +114,20 @@ The "Sign" action takes as input a purpose. It returns a signature or fails. # Derive the private key privkey for the scriptPubKey; FAIL if not VALID # Generate and return a signature sig with privkey=privkey, sighash=sighash +The resulting signature proof should be encoded using base64 encoding. + === Action: Verify === The "Verify" action takes as input a standard flags value, a script sig, an optional witness, and a purpose. It emits one of INCONCLUSIVE, VALID, INVALID, or ERROR. +While omitted below, ERROR is returned if an unforeseen error occurs at any point in the process. A concrete example of this is if a legacy proof is given as input to a non-legacy address; the deserialization of the proof will fail in this case, and this should result in an ERROR result. + # Obtain the sighash and scriptPubKey from the purpose; pass on result code if not VALID -# If one or more of the standard flags are unknown, return INCONCLUSIVE -# Verify Script with flags=standard flags, scriptSig=script sig, scriptPubKey=scriptPubKey, witness=witness, and sighash=sighash -# Return VALID if verify succeeds, otherwise return INVALID +# Verify Script with flags=consensus flags (currently P2SH, DERSIG, NULLDUMMY, CLTV, CSV, WITNESS), scriptSig=script sig, scriptPubKey=scriptPubKey, witness=witness, and sighash=sighash +# Return INVALID if verification fails +# Verify Script with flags=standard flags (above plus STRICTENC, MINIMALDATA, etc.), scriptSig=script sig, scriptPubKey=scriptPubKey, witness=witness, and sighash=sighash +# Return VALID if verification succeeds, otherwise return INCONCLUSIVE === Multiple Proofs === @@ -139,13 +139,40 @@ Note that the order of the entries in the proof must match the order of the entr * If a verification call returns ERROR or INVALID, return ERROR or INVALID immediately, ignoring as yet unverified entries * After all verifications complete, ** return INCONCLUSIVE if any verification call returned INCONCLUSIVE -** return SPENT if any verification call returned SPENT ** return INCOMPLETE if the INCOMPLETE flag is set ** return VALID +== Legacy format == + +The legacy format is restricted to the legacy P2PKH address format, and restricted to one single challenge (address). + +Any other input (e.g. multiple addresses, or non-P2PKH address format(s)) must be signed using the new format described above. + +=== Signing === + +Given the P2PKH address <code>a</code> and the message <code>m</code>, and the pubkey-hash function <code>pkh(P) = ripemd160(sha256(P))</code>: + +# let <code>p</code> be the pubkey-hash <code>pkh(P)</code> for the pubkey <code>P</code>, contained in <code>a</code> +# let <code>x</code> be the private key associated with <code>P</code> so that <code>pkh(xG) = p</code> +# let <code>digest</code> be <code>SHA56d("Bitcoin Signed Message:\n"||m)</code> +# create a compact signature <code>sig</code> (aka "recoverable ECDSA signature") using <code>x</code> on <code>digest</code> + +The resulting proof is <code>sig</code>, serialized using the base64 encoding. + +=== Verifying === + +Given the P2PKH address <code>a</code>, the message <code>m</code>, the compact signature <code>sig</code>, and the pubkey-hash function <code>pkh(P) = ripemd160(sha256(P))</code>: + +# let <code>p</code> be the pubkey-hash <code>pkh(P)</code> for the pubkey <code>P</code>, contained in <code>a</code> +# let <code>digest</code> be <code>SHA56d("Bitcoin Signed Message:\n"||m)</code> +# attempt pubkey recovery for <code>digest</code> using the signature <code>sig</code> and store the resulting pubkey into <code>Q</code> +## fail verification if pubkey recovery above fails +# let <code>q</code> be the pubkey-hash <code>pkh(Q)</code> for the pubkey <code>Q</code> +# if <code>p == q</code>, the proof is valid, otherwise it is invalid + == Compatibility == -This specification is not backwards compatible with the legacy signmessage/verifymessage specification. However, legacy addresses (1...) may be used in this implementation without any problems. +This specification is backwards compatible with the legacy signmessage/verifymessage specification through the special case as described above. == Rationale == @@ -153,17 +180,108 @@ This specification is not backwards compatible with the legacy signmessage/verif == Reference implementation == -To do. +# Pull request to Bitcoin Core: https://github.com/bitcoin/bitcoin/pull/16440 == Acknowledgements == -TODO +Thanks to David Harding, Jim Posen, Kalle Rosenbaum, Pieter Wuille, and many others for their feedback on the specification. == References == # Original mailing list thread: https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2018-March/015818.html -# Pull request, with comments: https://github.com/bitcoin/bips/pull/725 == Copyright == This document is licensed under the Creative Commons CC0 1.0 Universal license. + +== Consensus and standard flags == + +Each flag is associated with some type of enforced rule (most often a soft fork). There are two sets of flags: consensus flags (which result in a block being rejected, if violated), and policy flags (which result in a transaction being accepted only if it is contained within an actual block, and rejected otherwise, if violated). The policy flags are a super-set of the consensus flags. + +BIP322 specifies that a proof that validates for both rulesets is valid, a proof that validates for consensus rules, but not for policy rules, is "inconclusive", and a proof that does not validate for consensus rules is "invalid" (regardless of policy rule validation). + +The ruleset sometimes changes. This BIP does not intend to be complete, nor does it indicate enforcement of rules, it simply lists the rules as they stand at the point of writing. + +=== Consensus rules === + +* P2SH: evaluate P2SH ([https://github.com/bitcoin/bips/blob/master/bip-0016.mediawiki BIP16]) subscripts +* DERSIG: enforce strict DER ([https://github.com/bitcoin/bips/blob/master/bip-0066.mediawiki BIP66]) compliance +* NULLDUMMY: enforce NULLDUMMY ([https://github.com/bitcoin/bips/blob/master/bip-0147.mediawiki BIP147]) +* CHECKLOCKTIMEVERIFY: enable CHECKLOCKTIMEVERIFY ([https://github.com/bitcoin/bips/blob/master/bip-0065.mediawiki BIP65]) +* CHECKSEQUENCEVERIFY: enable CHECKSEQUENCEVERIFY ([https://github.com/bitcoin/bips/blob/master/bip-0112.mediawiki BIP112]) +* WITNESS: enable WITNESS ([https://github.com/bitcoin/bips/blob/master/bip-0141.mediawiki BIP141]) + +=== Policy rules === + +All of the above, plus (subject to change): + +* STRICTENC: non-strict DER signature or undefined hashtype +* MINIMALDATA: require minimal encodings for all push operations +* DISCOURAGE_UPGRADABLE_NOPS: discourage use of NOPs reserved for upgrades +* CLEANSTACK: require that only a single stack element remains after evaluation +* MINIMALIF: Segwit script only: require the argument of OP_IF/NOTIF to be exactly 0x01 or empty vector +* NULLFAIL: signature(s) must be empty vector if a CHECK(MULTI)SIG operation failed +* LOW_S: signature with S > order/2 in a checksig operation +* DISCOURAGE_UPGRADABLE_WITNESS_PROGRAM: v1-16 witness programs are non-standard (i.e. forbidden) +* WITNESS_PUBKEYTYPE: public keys in segregated witness scripts must be compressed +* CONST_SCRIPTCODE: OP_CODESEPARATOR and FindAndDelete fail any non-segwit scripts + +== Test vectors == + +== Native segwit test vector == + +<pre> +address = bcrt1qe7nte4zk4ayly5tc53dtdjupgkz0lr8azx3rzz +scriptpubkey = 0014cfa6bcd456af49f25178a45ab6cb814584ff8cfd +message = hello +preimage = 0014cfa6bcd456af49f25178a45ab6cb814584ff8cfd426974636f696e205369 + 676e6564204d6573736167653a0a68656c6c6f + (scriptpubkey || "Bitcoin Signed Message:\nhello") +sighash = 790eef86c204f0bff969ff822121317aa34eff0215dbd30ccf031e7b2f3f0cc1 + (sha256d(preimage), displayed in big-endian) +</pre> + +The proof becomes: + +<pre> +HEX: 01000000010002473044022075b4fb40421d55c55462879cb352a85eeb3af2138d3f0290 + 2c9143f12870f5f70220119c2995c1661138142f3899c1fd6d1af7e790e0e081be72db9c + e7bf5b5b932901210290beccd02b73eca57467b2b6f1e47161a9b76a5e67586e7c1dee9e + a6e2dcd869 + +Base64: AQAAAAEAAkcwRAIgdbT7QEIdVcVUYoecs1KoXus68hONPwKQLJFD8Shw9fcCIBGcKZXBZhE4 + FC84mcH9bRr355Dg4IG+ctuc579bW5MpASECkL7M0Ctz7KV0Z7K28eRxYam3al5nWG58He6e + puLc2Gk= +</pre> + +Split into components: + +{|class="wikitable" style="text-align: center;" +|- +!Type +!Length +!Name +!Value +!Comment +|- +|Uint32||4||flags||<code>01000000</code>||proof format version +|- +|Uint8||1||entries||<code>01</code>||1 entry +|- +|VarInt||1-8||scriptsiglen||<code>00</code>||0 byte scriptsig +|- +|VarInt||1-8||wit entries||<code>02</code>||2 witness stack entries +|- +|VarInt||1-8||entry1len||<code>47</code>||71 byte entry +|- +|Uint8[71]||71||entry1||<code>3044022075b4fb40421d55c55462879cb352a85eeb3af213 +8d3f02902c9143f12870f5f70220119c2995c1661138142f +3899c1fd6d1af7e790e0e081be72db9ce7bf5b5b932901</code>||Witness stack item 1 +|- +|VarInt||1-8||entry2len||<code>21</code>||33 byte entry +|- +|Uint8[33]||33||entry2||<code>0290beccd02b73eca57467b2b6f1e47161a9b76a5e67586e +7c1dee9ea6e2dcd869</code>||Witness stack item 2 +|} + +The above test vector is for a bech32 P2WPKH (native segwit) address. (Once BIP solidifies, will add test vector for other types.) |