BIP 322: Generic Signed Message Format

  BIP: 322
  Layer: Applications
  Title: Generic Signed Message Format
  Authors: Karl-Johan Alm <karljohan-alm@garage.co.jp>
  Deputies: guggero <gugger@gmail.com>
  Status: Complete
  Type: Specification
  Assigned: 2018-09-10
  License: CC0-1.0
  Discussion: 2018-03-14: https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2018-March/015818.html
              2019-07-23: https://github.com/bitcoin/bitcoin/pull/16440
              2022-01-13: https://github.com/bitcoin/bitcoin/pull/24058
              2022-08-06: https://bitcointalk.org/index.php?topic=5408898.0
              2024-05-04: https://groups.google.com/g/bitcoindev/c/RCi1Exs0ZvQ/m/vp6Xo36aBwAJ
              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

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.

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 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 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.)

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.

Finally, this BIP only addresses the use case where a signer shows they will be able to control funds sent to the invoice address. Proving that a signer sent a prior transaction is not possible 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 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 on what is required to satisfy the script corresponding to the message_challenge.

Types of Signatures

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.

	Compatible script types	Signature prefix	Signature format
Legacy	`P2PKH`, `P2SH-P2WPKH`¹, `P2WPKH`¹	n/a	compact, public key recoverable ECDSA signature, base64-encoded
Simple	`P2WPKH`, `P2WSH`², `P2TR`²	`smp`	witness stack, consensus encoded and base64-encoded
Full	`all`	`ful`	full `to_sign` transaction, consensus and base64-encoded
Full (Proof of Funds)	`all`	`pof`	full finalized PSBT of the `to_sign` transaction, consensus and base64-encoded

¹: Possible on a technical level but should NOT be used anymore in the context of this BIP.
²: Excluding time lock scripts.

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.

The legacy format MAY be used, but must be restricted to the legacy P2PKH invoice address format.

Simple

A simple signature consists of a witness stack, consensus encoded as a vector of vectors of bytes, and base64-encoded, prefixed by the variant (smp). Validators should construct to_spend and to_sign as defined below, with default values for all fields except that

``` message_hash is a BIP340-tagged hash of the message, as specified below
message_challenge in to_spend is set to the scriptPubKey being signed with
message_signature in to_sign is set to the provided simple signature.

```

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 Signet.

Let there be two virtual transactions to_spend and to_sign.

The to_spend transaction is:

    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

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.

The to_sign transaction is:

    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
    vin[0].nSequence = 0 or (FULL format only) as appropriate (for time locks)
    vin[0].scriptSig = [] or (FULL format only) as appropriate (for non segwit-native transactions)
    vin[0].scriptWitness = message_signature
    vout[0].nValue = 0
    vout[0].scriptPubKey = OP_RETURN

A full signature consists of the variant-prefixed (ful) base64-encoding of the to_sign transaction in standard network serialisation once it has been signed.

Full (Proof of Funds)

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 process).
All outputs that the signer wishes to demonstrate control of are included as additional inputs of to_sign, and their witness and scriptSig data should be set as though these outputs were actually being spent.
The Non-Witness or Witness UTXO fields (as appropriate for the type) of each additional input must be set to the corresponding UTXO.
As an optimization for large sets of Non-Witness UTXOs that spend outputs from the same transaction, the Non-Witness UTXO field may be omitted for any input that spends an output from the same transaction as an input earlier in the list.

```

A full Proof of Funds signature consists of the variant-prefixed (pof) base64-encoding of the finalized PSBT once it has been signed.

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 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 address.

Detailed Specification

For all signature types, except legacy, the to_spend and to_sign transactions must be valid transactions which pass all consensus checks, except of course that the 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

``` ''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

```

Verification Process

Validation consists of the following steps:

Basic validation
1. Compute the transaction to_spend from m and A
2. Decode s as the transaction to_sign
3. If s was a full transaction or PSBT, confirm all fields are set as specified above; in particular that
4. - to_sign has at least one input and its first input spends the output of to_spend
5. - to_sign with more than one input has an appropriate Witness UTXO or Non-Witness UTXO for each input
6. ** 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
7. - to_sign has exactly one output, as specified above
8. 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:
1. All signatures must use the SIGHASH_ALL flag.
2. The use of CODESEPARATOR or FindAndDelete is forbidden.
3. 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
4. MINIMALDATA: all pushes must be minimally encoded
5. CLEANSTACK: require that only a single stack element remains after evaluation
6. MINIMALIF: the argument of IF/NOTIF must be exactly 0x01 or empty push
7. If any of the above steps failed, the validator should stop and output the invalid state.
Check the upgradeable rules
1. The version of to_sign must be 0 or 2.
2. The use of NOPs reserved for upgrades is forbidden.
3. The use of Segwit versions greater than 1 are forbidden.
4. 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.

Signing

Signers who control an address A who wish to sign a message m act as follows:

``` They construct to_spend and to_sign as specified above, using the scriptPubKey of ''A'' for message_challenge and tagged hash of ''m'' as message_hash.
Optionally, they may set nVersion/nLockTime of to_sign or nSequence of its first input.
Optionally, they may add any additional inputs to to_sign that they wish to prove control of.
They satisfy to_sign as they would any other transaction.

```

They then encode their signature, choosing either simple, full or full-pof as follows:

``` 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.
If they added no inputs to to_sign, they may base64-encode to_sign with ful as prefix.
Otherwise, they must base64-encode the finalized PSBT of to_sign with pof as prefix.

```

PSBT-based signing

A valid witness stack for a multisig address must be constructed by coordinating different signers to produce a partial signature each. The coordination procedure is not specified by this BIP, but due to the use of PSBTs it should closely resemble the coordination of signing a multisig transaction for publishing to the network.

The main difference is a new global PSBT field and the way a signer presents the transaction signing request to the user. The new global type is defined as follows:

Name	`<keytype>`	`<keydata>`	`<keydata>` Description	`<valuedata>`	`<valuedata>` Description	Versions Requiring Inclusion	Versions Requiring Exclusion	Versions Allowing Inclusion
Generic Signed Message	`PSBT_GLOBAL_GENERIC_SIGNED_MESSAGE = 0x09`	None	No key data	`<bytes message>`	The UTF-8 encoded message to be signed.			0, 2

PSBT creator

The transaction creator of a BIP-0322 PSBT must follow these steps:

``` They construct to_spend and to_sign as specified above, using the scriptPubKey of ''A'' for message_challenge and tagged hash of ''m'' as message_hash.
Optionally, they may set nVersion/nLockTime of to_sign or nSequence of its first input.
Optionally, they may add any additional inputs to to_sign that they wish to prove control of.
They set the appropriate witness_utxo and non_witness_utxo fields of the first input, using the to_spend transaction as a non_witness_utxo or the first output of the to_spend transaction as witness_utxo.
They set the appropriate witness_utxo and non_witness_utxo fields of each additional input.
They set the appropriate PSBT input and global fields as required by the signers(s) to produce a partial signature.
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 recommended to use a maximum length of a few kilobytes to maximize compatibility. Very large messages should be committed to by hash instead.

```

PSBT signer

A transaction signer of a BIP-0322 PSBT must follow these steps:

``` They decode the base64-encoded PSBT as specified in [[bip-0174.mediawiki|BIP-0174]].
If they detect the following properties (all must be true, otherwise this is NOT a BIP-0322 PSBT and they should treat it as an ordinary PSBT):
1. The PSBT has the PSBT_GLOBAL_GENERIC_SIGNED_MESSAGE field set. Extract and use as message in the next 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 message_challenge in the next steps.
3. The first PSBT input has prevout.n = 0.
4. The first PSBT input has prevout.hash = to_spend.txid where to_spend.txid is constructed using the rules described above using the message and message_challenge from the previous steps.
5. The PSBT's unsigned transaction has a single output with a value of 0 and the scriptPubKey set to OP_RETURN (0x6a).
If all of the above steps are true, the signer must inform the user about the message they are 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 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. Example: Instead of showing "spending 0 satoshi from address <challenge_address>" the device should show "signing message <message> for address <challenge_address>".
Upon user approval, the signer adds a partial signature for each input it is capable of signing.

```

PSBT finalizer

A transaction finalizer of a BIP-0322 PSBT must follow these steps:

``` They decode the base64-encoded PSBT as specified in [[bip-0174.mediawiki|BIP-0174]].
They finalize the PSBT as specified in [[bip-0174.mediawiki#input-finalizer|BIP-0174]].
They then encode the signature following the same steps as described in [[bip-0322.mediawiki#signing|Signing]] above.

```

Compatibility

This specification is backwards compatible with the legacy signmessage/verifymessage specification through the special case 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.

Reference implementation

``` Bitcoin Core pull request (basic support) at: https://github.com/bitcoin/bitcoin/pull/24058
btcd pull request (complete support, source of test vectors) at: https://github.com/btcsuite/btcd/pull/2521

```

Acknowledgements

Thanks to David Harding, Jim Posen, Kalle Rosenbaum, Pieter Wuille, Andrew Poelstra, Luke Dashjr, 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

```

Changelog

1.0.0 (2026-04-15):
- Mark Complete
- Breaking change: Add human-readable prefix to encoded signature
- Breaking change: format of "Proof of Funds" signatures to be base64-encoded finalized PSBT
- Add new PSBT input field for PSBT-based signing
0.0.1 (2018-09-10):
- Proposed as draft

Copyright

This document is licensed under the Creative Commons CC0 1.0 Universal license.

Test vectors

Basic test vectors for message hashing, transaction hashes and "simple" variant test cases can be found in basic-test-vectors.json.

Generated test vectors for more "simple" and "full" variant test cases can be found in generated-test-vectors.json.

They were generated using this code.