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Diffstat (limited to 'bip-0322.mediawiki')
| -rw-r--r-- | bip-0322.mediawiki | 265 |
1 files changed, 91 insertions, 174 deletions
diff --git a/bip-0322.mediawiki b/bip-0322.mediawiki index 95991e6..5f4704d 100644 --- a/bip-0322.mediawiki +++ b/bip-0322.mediawiki @@ -13,123 +13,130 @@ == Abstract == -A standard for interoperable generic signed messages based on the Bitcoin Script format. +A standard for interoperable signed messages based on the Bitcoin Script format, either for proving fund availability, or committing to a message as the intended recipient of funds sent to the invoice address. -== Background == +== Motivation == -* 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 current message signing standard only works for P2PKH (1...) invoice addresses. We propose to extend and generalize the standard by using a Bitcoin Script based approach. This ensures that any coins, no matter what script they are controlled by, can in-principle be signed for. For easy interoperability with existing signing hardware, we also define a signature message format which resembles a Bitcoin transaction (except that it contains an invalid input, so it cannot be spent on any real network). -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. +Additionally, the current message signature format uses ECDSA signatures which do not commit to the public key, meaning that they do not actually prove knowledge of any secret keys. (Indeed, valid signatures can be tweaked by 3rd parties to become valid signatures on certain related keys.) -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. +Ultimately no message signing protocol can actually prove control of funds, both because a signature is obsolete as soon as it is created, and because the possessor of a secret key may be willing to sign messages on others' behalf even if it would not sign actual transactions. No signmessage protocol can fix these limitations. -== Motivation == +== Types of Signatures == -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. +This BIP specifies three formats for signing messages: ''legacy'', ''simple'' and ''full''. Additionally, a variant of the ''full'' format can be used to demonstrate control over a set of UTXOs. -== Specification == +=== Legacy === -A new structure <code>SignatureProof</code> is added, which is a simple serializable scriptSig & witness container. +New proofs should use the new format for all invoice address formats, including P2PKH. -=== SignatureProof container === +The legacy format MAY be used, but must be restricted to the legacy P2PKH invoice address format. -{|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 entries in witness stack -|- -|Uint8[]*||[witlen]||wit||Witness stack, as [witlen] uint8* vectors, each one prepended with a varint of its size -|} +=== Simple === -In some cases, the scriptsig or wit may be empty. If both are empty, the proof is incomplete. +A ''simple'' signature consists of a witness stack, consensus encoded as a vector of vectors of bytes, and base64-encoded. Validators should construct <code>to_spend</code> and <code>to_sign</code> as defined below, with default values for all fields except that -=== Result Codes === +* <code>message_hash</code> is a BIP340-tagged hash of the message, as specified below +* <code>message_challenge</code> in <code>to_spend</code> is set to the scriptPubKey being signed with +* <code>message_signature</code> in <code>to_sign</code> is set to the provided simple signature. -A verification call will return a result code according to the table below. +and then proceed as they would for a full signature. -{|class="wikitable" style="text-align: center;" -|- -!Code -!Description -|- -|INCOMPLETE||Empty proof. -|- -|INCONCLUSIVE||The given proof was consensus-valid but policy-invalid. -|- -|VALID||The proof was valid. -|- -|INVALID||The proof was invalid -|- -|ERROR||An error was encountered -|} +=== Full === -== Signing and Verifying == +Full signatures follow an analogous specification to the BIP-325 challenges and solutions used by Signet. -If the challenge consists of an address is in the P2PKH (legacy) format, sign using the legacy format (further information below). Otherwise continue as stated below. +Let there be two virtual transactions <code>to_spend</code> and <code>to_sign</code>. -For both cases, generate a sighash based on the given scriptPubKey and message as follows: +The <code>to_spend</code> transaction is: -# 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)) + nVersion = 0 + nLockTime = 0 + vin[0].prevout.hash = 0000...000 + vin[0].prevout.n = 0xFFFFFFFF + vin[0].nSequence = 0 + vin[0].scriptSig = OP_0 PUSH32[ message_hash ] + vin[0].scriptWitness = [] + vout[0].nValue = 0 + vout[0].scriptPubKey = message_challenge -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. +where <code>message_hash</code> is a BIP340-tagged hash of the message, i.e. sha256_tag(m), where tag = <code>BIP0322-signed-message</code>, and <code>message_challenge</code> is the to be proven (public) key script. -=== Signing === +The <code>to_sign</code> transaction is: -The signature is generated as follows: + nVersion = 0 or as appropriate (e.g. 2, for time locks) + nLockTime = 0 or as appropriate (for time locks) + vin[0].prevout.hash = to_spend.txid + vin[0].prevout.n = 0 + vin[0].nSequence = 0 or as appropriate (for time locks) + vin[0].scriptWitness = message_signature + vout[0].nValue = 0 + vout[0].scriptPubKey = OP_RETURN -# Derive the private key privkey for the scriptPubKey; FAIL if not VALID -# Generate and return a signature sig with privkey=privkey, sighash=sighash +A full signature consists of the base64-encoding of the <code>to_sign</code> transaction in standard network serialisation. -=== Verifying === +=== Full (Proof of Funds) === -Verify a proof, given a standard flags value, a script sig, an optional witness, and a derived sighash as described above. +A signer may construct a proof of funds, demonstrating control of a set of UTXOs, by constructing a full signature as above, with the following modifications. -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. +* <code>message_challenge</code> is unused and shall be set to <code>OP_TRUE</code> +* Similarly, <code>message_signature</code> is then empty. +* All outputs that the signer wishes to demonstrate control of are included as additional inputs of <code>to_sign</code>, and their witness and scriptSig data should be set as though these outputs were actually being spent. -# 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 +Unlike an ordinary signature, validators of a proof of funds need access to the current UTXO set, to learn that the claimed inputs exist on the blockchain, and to learn their scriptPubKeys. -== Legacy format == +== Detailed Specification == -The legacy format is restricted to the legacy P2PKH address format. +For all signature types, except legacy, the <code>to_spend</code> and <code>to_sign</code> transactions must be valid transactions which pass all consensus checks, except of course that the output with prevout <code>000...000:FFFFFFFF</code> does not exist. -Any other input (i.e. non-P2PKH address format) must be signed using the new format described above. +=== Verification === -=== Signing === +A validator is given as input an address ''A'' (which may be omitted in a proof-of-funds), signature ''s'' and message ''m'', and outputs one of three states +* ''valid at time T and age S'' indicates that the signature has set timelocks but is otherwise valid +* ''inconclusive'' means the validator was unable to check the scripts +* ''invalid'' means that some check failed -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>: +==== Verification Process ==== -# 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> +Validation consists of the following steps: + +# Basic validation +## Compute the transaction <code>to_spend</code> from ''m'' and ''A'' +## Decode ''s'' as the transaction <code>to_sign</code> +## If ''s'' was a full transaction, confirm all fields are set as specified above; in particular that +##* <code>to_sign</code> has at least one input and its first input spends the output of </code>to_spend</code> +##* <code>to_sign</code> has exactly one output, as specified above +## Confirm that the two transactions together satisfy all consensus rules, except for <code>to_spend</code>'s missing input, and except that ''nSequence'' of <code>to_sign</code>'s first input and ''nLockTime'' of <code>to_sign</code> are not checked. +# (Optional) If the validator does not have a full script interpreter, it should check that it understands all scripts being satisfied. If not, it should stop here and output ''inconclusive''. +# Check the **required rules**: +## All signatures must use the SIGHASH_ALL flag. +## The use of <code>CODESEPARATOR</code> or <code>FindAndDelete</code> is forbidden. +## <code>LOW_S</code>, <code>STRICTENC</code> and <code>NULLFAIL</code>: valid ECDSA signatures must be strictly DER-encoded and have a low-S value; invalid ECDSA signature must be the empty push +## <code>MINIMALDATA</code>: all pushes must be minimally encoded +## <code>CLEANSTACK</code>: require that only a single stack element remains after evaluation +## <code>MINIMALIF</code>: the argument of <code>IF</code>/<code>NOTIF</code> must be exactly 0x01 or empty push +## If any of the above steps failed, the validator should stop and output the ''invalid'' state. +# Check the **upgradeable rules** +## The version of <code>to_sign</code> must be 0 or 2. +## The use of NOPs reserved for upgrades is forbidden. +## The use of segwit versions greater than 0 are forbidden. +## If any of the above steps failed, the validator should stop and output the ''inconclusive'' state. +# Let ''T'' by the nLockTime of <code>to_sign</code> and ''S'' be the nSequence of the first input of <code>to_sign</code>. Output the state ''valid at time T and age S''. + +=== Signing === -The resulting proof is <code>sig</code>, serialized using the base64 encoding. +Signers who control an address ''A'' who wish to sign a message ''m'' act as follows: -=== Verifying === +# They construct <code>to_spend</code> and <code>to_sign</code> as specified above, using the scriptPubKey of ''A'' for <code>message_challenge</code> and tagged hash of ''m'' as <code>message_hash</code>. +# Optionally, they may set nLockTime of <code>to_sign</code> or nSequence of its first input. +# Optionally, they may add any additional outputs to <code>to_sign</code> that they wish to prove control of. +# They satisfy <code>to_sign</code> as they would any other transaction. -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>: +They then encode their signature, choosing either ''simple'' or ''full'' as follows: -# 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 +* If they added no inputs to <code>to_sign</code>, left nSequence and nLockTime at 0, and ''A'' is a Segwit address (either pure or P2SH-wrapped), then they may base64-encode <code>message_signature</code> +* Otherwise they must base64-encode <code>to_sign</code>. == Compatibility == @@ -137,11 +144,11 @@ This specification is backwards compatible with the legacy signmessage/verifymes == Reference implementation == -# Pull request to Bitcoin Core: https://github.com/bitcoin/bitcoin/pull/16440 +TODO == Acknowledgements == -Thanks to David Harding, Jim Posen, Kalle Rosenbaum, Pieter Wuille, and many others for their feedback on the specification. +Thanks to David Harding, Jim Posen, Kalle Rosenbaum, Pieter Wuille, Andrew Poelstra, and many others for their feedback on the specification. == References == @@ -151,96 +158,6 @@ Thanks to David Harding, Jim Posen, Kalle Rosenbaum, Pieter Wuille, and many oth 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 == -(TODO: update test vectors, which are based on previous iteration where signature proofs contained additional data) - -== 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.) +TODO |