diff --git a/README.mediawiki b/README.mediawiki index cb043f2a29..8ff1a8c38a 100644 --- a/README.mediawiki +++ b/README.mediawiki @@ -1076,7 +1076,7 @@ users (see also: [https://en.bitcoin.it/wiki/Economic_majority economic majority | [[bip-0322.mediawiki|322]] | Applications | Generic Signed Message Format -| Karl-Johan Alm +| Karl-Johan Alm, Oliver Gugger | Specification | Complete |- style="background-color: #cfffcf" diff --git a/bip-0322.mediawiki b/bip-0322.mediawiki index d4a6bfd8b4..e29a32ba89 100644 --- a/bip-0322.mediawiki +++ b/bip-0322.mediawiki @@ -3,7 +3,7 @@ Layer: Applications Title: Generic Signed Message Format Authors: Karl-Johan Alm - Deputies: guggero + Oliver Gugger Status: Complete Type: Specification Assigned: 2018-09-10 @@ -16,35 +16,29 @@ 2025-05-10: https://bitcoin.stackexchange.com/questions/126277/where-can-i-use-bip322-to-sign-a-message-to-verify-a-multisig-address 2026-04-20: https://groups.google.com/g/bitcoindev/c/qd6BNz9gxCk/m/k1fHq4RKAQAJ Version: 1.0.0 + Requires: 174, 340, 341 == Abstract == 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. +availability of funds, or for committing to a message as the intended recipient of funds sent to the +invoice address. == Motivation == 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 +extend and generalize the standard by using an approach based on Bitcoin Script. 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 that resembles a Bitcoin transaction (except that it contains an invalid input, so it cannot be spent on any real network). -The Proof of Funds variant allows demonstrating control of a set of UTXOs. -The list of UTXOs may or may not be related to the address being signed with (the -message_challenge). -But in any case, the UTXO list does not aim to prove completeness (e.g. it does NOT mean: -"these are all UTXOs that exist for an address") nor that they are unspent (e.g. a -validator must consult the blockchain to verify that). - -Additionally, the current message signature format uses ECDSA signatures which do not commit to the +Additionally, the current message signature format uses ECDSA signatures that 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.) +signatures can be tweaked by third parties to become valid signatures on certain related keys.) -Ultimately no message signing protocol can actually prove control of funds, both because a 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 message signing protocol can fix these limitations. @@ -56,7 +50,7 @@ using this BIP. == Terminology == In the context of this BIP, whenever the word "signature" or similar is used, it refers to the -output of the signing process described below and, depending on the script type of the +output of the signing process described below, and, depending on the script type of the message_challenge, is either a full transaction input witness stack, a full transaction, or a PSBT packet that can be validated against a Bitcoin Script Interpreter. Such a "signature" may or may not contain an actual cryptographic (ECDSA or Schnorr) signature, depending @@ -83,32 +77,32 @@ UTXOs. | Simple | P2WPKH, P2WSH2, P2TR2
| smp -| witness stack, consensus encoded and base64-encoded +| witness stack, consensus-encoded and base64-encoded |- | Full | all | ful -| full to_sign transaction, consensus and base64-encoded +| full to_sign transaction, consensus-encoded and base64-encoded |- | Full (Proof of Funds) | all | pof -| full finalized PSBT of the to_sign transaction, consensus and base64-encoded +| full finalized PSBT of the to_sign transaction, consensus-encoded and base64-encoded |} -1: Possible on a technical level but should NOT be used anymore in the context of this -BIP.
+1: Possible on a technical level but SHOULD NOT be used anymore in the context of this +BIP, see section [[#legacy|Legacy]] below.
2: Excluding time lock scripts. -Signers must prefix the signature with the variant that was used to create the signature. +Signers MUST prefix the signature with the variant that was used to create the signature. To support backward compatibility with implementations of this BIP before it was finalized, a verifier might assume the ''simple'' variant in the absence of a prefix. === Legacy === -New proofs should use the new format for all invoice address formats, including P2PKH. +New proofs SHOULD use the new format for all invoice address formats, including P2PKH. -The legacy format MAY be used, but must be restricted to the legacy P2PKH invoice address format. +The legacy format MAY be used, but MUST be restricted to the legacy P2PKH invoice address format. === Simple === @@ -134,7 +128,7 @@ and then proceed as they would for a full signature. === Full === -Full signatures follow an analogous specification to the BIP-325 challenges and solutions used by +Full signatures follow an analogous specification to the BIP325 challenges and solutions used by Signet. Let there be two virtual transactions to_spend and to_sign. @@ -151,14 +145,14 @@ The to_spend transaction is: vout[0].nValue = 0 vout[0].scriptPubKey = message_challenge -where message_hash is a BIP340-tagged hash of the message, i.e. sha256_tag(m), where -tag = BIP0322-signed-message and m is the message as is without length -prefix or null terminator, and message_challenge is the to be proven (public) key -script. +where message_hash is a BIP340-tagged hash of the message, i.e., sha256_tag(m), where +tag = BIP0322-signed-message and m is the message as-is without length +prefix or null terminator, and message_challenge is the (public) key script to be +proven. The to_sign transaction is: - nVersion = 0 or (FULL format only) as appropriate (e.g. 2, for time locks) + nVersion = 0 or (FULL format only) as appropriate (e.g., 2 for time locks) nLockTime = 0 or (FULL format only) as appropriate (for time locks) vin[0].prevout.hash = to_spend.txid vin[0].prevout.n = 0 @@ -173,13 +167,22 @@ A ''full'' signature consists of the variant-prefixed (ful) base64- === Full (Proof of Funds) === +The [[#full-proof-of-funds|Proof of Funds]] variant extends the basic scheme: in addition to signing +a message under a single address's key, the signer proves control over an arbitrary set of UTXOs. +This UTXO set is chosen freely by the signer and MAY be associated with the signing address +(the message_challenge). For example, it may consist of outputs paid to that address, +but any UTXOs the signer wants to show control over are permitted. +In any case, however, the UTXO list does not aim to prove completeness (e.g., it does NOT mean: +"these are all UTXOs that exist for an address"), nor that they are unspent (e.g., a validator must +consult the blockchain to verify that). + 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.
  • The to_spend transaction is represented as a finalized PSBT instead of a raw - transaction (see [[bip-0174.mediawiki#input-finalizer|BIP-0174]] for details on the finalization + transaction (see [[bip-0174.mediawiki#input-finalizer|BIP174]] for details on the finalization process).
  • @@ -205,7 +208,7 @@ Unlike an ordinary signature, validators of a proof of funds need access to the learn that the claimed inputs exist on the blockchain and remain unspent. An offline validator therefore can only attest to the cryptographic validity of the additional inputs' witness stack, but not its blockchain state. -An attested list of UTXOs can also never prove that there don't exist more UTXOs for a certain +An attested list of UTXOs can also never prove that there do not exist more UTXOs for a certain address. == Detailed Specification == @@ -217,7 +220,7 @@ output with prevout 000...000:FFFFFFFF does not exist. === Verification === 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 +''s'' and message ''m'', and outputs one of three states:
    • @@ -240,14 +243,14 @@ Validation consists of the following steps: ## Compute the transaction to_spend from ''m'' and ''A'' ## Decode ''s'' as the transaction to_sign ## If ''s'' was a full transaction or PSBT, confirm all fields are set as specified above; in particular that -##* to_sign has at least one input and its first input spends the output of to_spend +##* to_sign has at least one input and its first input spends the output of to_spend ##* to_sign with more than one input has an appropriate Witness UTXO or Non-Witness UTXO for each input ##** If (based on the input type) a Non-Witness UTXO is required but not provided, check if the first input with the same transaction ID has a Non-Witness UTXO set and use that; fail validation if no such Non-Witness UTXO can be found ##* to_sign has exactly one output, as specified above ## Confirm that the two transactions together satisfy all consensus rules, except for to_spend's missing input, and except that ''nSequence'' of to_sign's first input and ''nLockTime'' of to_sign 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. +## All signatures MUST use the SIGHASH_ALL flag, unless the output type supports SIGHASH_DEFAULT, which then MAY be used alternatively (e.g., [[bip-0341.mediawiki|BIP341 P2TR]]). ## The use of CODESEPARATOR or FindAndDelete is forbidden. ## LOW_S, STRICTENC and NULLFAIL: valid ECDSA signatures must be strictly DER-encoded and have a low-S value; invalid ECDSA signature must be the empty push ## MINIMALDATA: all pushes must be minimally encoded @@ -259,7 +262,7 @@ Validation consists of the following steps: ## The use of NOPs reserved for upgrades is forbidden. ## The use of Segwit versions greater than 1 are forbidden. ## If any of the above steps failed, the validator should stop and output the ''inconclusive'' state. -# Let ''T'' by the nLockTime of to_sign and ''S'' be the nSequence of the first input of to_sign. Output the state ''valid at time T and age S''. +# Let ''T'' be the nLockTime of to_sign and ''S'' be the nSequence of the first input of to_sign. Output the state ''valid at time T and age S''. === Signing === @@ -290,7 +293,7 @@ They then encode their signature, choosing either ''simple'', ''full'' or ''full
    • If they added no inputs to to_sign, left nVersion, nSequence and nLockTime at 0, and ''A'' is a "native" Segwit address (P2WPKH, P2WSH, P2TR), then they may base64-encode - message_signature with smp as prefix. + message_signature with smp as prefix.
    • If they added no inputs to to_sign, they may base64-encode to_sign with @@ -336,7 +339,7 @@ request to the user. The new global type is defined as follows: === PSBT creator === -The '''transaction creator''' of a BIP-0322 PSBT must follow these steps: +The '''transaction creator''' of a BIP322 PSBT must follow these steps:
      1. @@ -366,12 +369,12 @@ The '''transaction creator''' of a BIP-0322 PSBT must follow these steps: partial signature.
      2. - They set the PSBT_GLOBAL_GENERIC_SIGNED_MESSAGE field, using the full UTF-8 encoded + They set the PSBT_GLOBAL_GENERIC_SIGNED_MESSAGE field, using the full UTF-8-encoded message as the valuedata.
        1. There is no specified maximum length of an input's valuedata or a PSBT as a whole in - [[bip-0174.mediawiki|BIP-0174]], but different signers might impose safety limits. It is + [[bip-0174.mediawiki|BIP174]], but different signers might impose safety limits. It is recommended to use a maximum length of a few kilobytes to maximize compatibility. Very large messages should be committed to by hash instead.
          2. @@ -381,14 +384,14 @@ The '''transaction creator''' of a BIP-0322 PSBT must follow these steps: === PSBT signer === -A '''transaction signer''' of a BIP-0322 PSBT must follow these steps: +A '''transaction signer''' of a BIP322 PSBT must follow these steps:
          1. - They decode the base64-encoded PSBT as specified in [[bip-0174.mediawiki|BIP-0174]]. + They decode the base64-encoded PSBT as specified in [[bip-0174.mediawiki|BIP174]].
          2. - If they detect the following properties (all must be true, otherwise this is NOT a BIP-0322 PSBT + If they detect the following properties (all must be true, otherwise this is NOT a BIP322 PSBT and they should treat it as an ordinary PSBT):
            1. @@ -397,7 +400,7 @@ A '''transaction signer''' of a BIP-0322 PSBT must follow these steps:
            2. The first PSBT input has either a witness_utxo or a non_witness_utxo - field set and the scriptPubKey can be extracted, then use as + field set and the scriptPubKey can be extracted. Use that as message_challenge in the next steps.
            3. @@ -419,7 +422,7 @@ A '''transaction signer''' of a BIP-0322 PSBT must follow these steps: signing and the address they are signing for.
              1. - Even though the message being signed is a transaction, the user interaction (e.g. the steps and + Even though the message being signed is a transaction, the user interaction (e.g., the steps and messages shown on a hardware signing device's screen) should resemble the steps to sign a legacy message, not the steps for signing a transaction.
                2. @@ -436,25 +439,25 @@ A '''transaction signer''' of a BIP-0322 PSBT must follow these steps: === PSBT finalizer === -A '''transaction finalizer''' of a BIP-0322 PSBT must follow these steps: +A '''transaction finalizer''' of a BIP322 PSBT must follow these steps:
                1. - They decode the base64-encoded PSBT as specified in [[bip-0174.mediawiki|BIP-0174]]. + They decode the base64-encoded PSBT as specified in [[bip-0174.mediawiki|BIP174]].
                2. - They finalize the PSBT as specified in [[bip-0174.mediawiki#input-finalizer|BIP-0174]]. + They finalize the PSBT as specified in [[bip-0174.mediawiki#input-finalizer|BIP174]].
                3. - They then encode the signature following the same steps as described in - [[bip-0322.mediawiki#signing|Signing]] above. + They then encode the signature following the same steps as described in [[#signing|Signing]] + above.
                == Compatibility == -This specification is backwards compatible with the legacy signmessage/verifymessage specification -through the special case as described above. +This specification is backwards-compatible with the legacy signmessage/verifymessage specification +through the special case [[#legacy|as described above]]. To support backward compatibility with implementations of this BIP before it was finalized, a verifier might assume the ''simple' variant in the absence of a prefix.