Skip to content

Latest commit

 

History

History
531 lines (457 loc) · 34.9 KB

bip-0174.mediawiki

File metadata and controls

531 lines (457 loc) · 34.9 KB
Raw

  BIP: 174
  Layer: Applications
  Title: Partially Signed Bitcoin Transaction Format
  Author: Andrew Chow <achow101@gmail.com>
  Comments-Summary: No comments yet.
  Comments-URI: https://github.com/bitcoin/bips/wiki/Comments:BIP-0174
  Status: Draft
  Type: Standards Track
  Created: 2017-07-12
  License: BSD-2-Clause

Table of Contents

Introduction

Abstract

This document proposes a binary transaction format which contains the information necessary for a signer to produce signatures for the transaction and holds the signatures for an input while the input does not have a complete set of signatures. The signer can be offline as all necessary information will be provided in the transaction.

Copyright

This BIP is licensed under the 2-clause BSD license.

Motivation

Creating unsigned or partially signed transactions to be passed around to multiple signers is currently implementation dependent, making it hard for people who use different wallet software from being able to easily do so. One of the goals of this document is to create a standard and extensible format that can be used between clients to allow people to pass around the same transaction to sign and combine their signatures. The format is also designed to be easily extended for future use which is harder to do with existing transaction formats.

Signing transactions also requires users to have access to the UTXOs being spent. This transaction format will allow offline signers such as air-gapped wallets and hardware wallets to be able to sign transactions without needing direct access to the UTXO set and without risk of being defrauded.

Specification

The Partially Signed Bitcoin Transaction (PSBT) format consists of key-value maps. Each key-value pair must be unique within its scope; duplicates are not allowed. Each map consists of a sequence of records, terminated by a 0x00 byte [1]. The format of a record is as follows:

Note: <..> indicates that the data is prefixed by a compact size unsigned integer representing the length of that data. {..} indicates the raw data itself. 

<key>|<value>

Name Type Description
Key Length Compact Size Unsigned Integer Specify how long the key is
Key byte[] The key itself with the first byte being the type of the key-value pair
Value Length Compact Size Unsigned Integer Specify how long the value is
Value byte[] The Value itself

The format of each key-value map is as follows: 

{key-value pair}|{key-value pair}|...|{0x00}

Field Size Name Type Value Description
1+ Key-value pairs Array of key-value pairs varies The key-value pairs.
1 separator char 0x00 Must be 0x00.

The first byte of each key specifies the type of the key-value pair. Some types are for global fields and other fields are for each input. The only required type in a PSBT is the transaction type, as defined below. All global types that can pertain to both inputs and outputs of a transaction can include data for both inputs and outputs of the transaction. The currently defined global types are as follows:

Number Name Key Data Value Data Format Example
0x00 Transaction None. The key must only contain the 1 byte type. The transaction in network serialization. The scriptSigs and witnesses for each input must be empty unless the input is complete. The transaction must be in the witness serialization format as defined in BIP 144. A PSBT must have a transaction, otherwise it is invalid. Key: 
{0x00}
Value: 
{transaction}
0x01 Redeem Script[2] The hash160 of the redeem script A redeem script that will be needed to sign a Pay-To-Script-Hash input or is spent to by an output.[3] Key: 
{0x01}|{hash160}
Value: 
{redeem script}
0x02 Witness Script The sha256 hash of the witness script A witness script that will be needed to sign a Pay-To-Witness-Script-Hash input or is spent to by an output. Key: 
{0x02}|{sha256}
Value: 
{witness script}
0x03 BIP 32 Derivation path, public key, and Master Key fingerprint The public key The master key fingerprint concatenated with the derivation path of the public key. The derivation path is represented as 32 bit unsigned integer indexes concatenated with each other. This must omit the index of the master key. Public keys can be those that will be needed to sign any type of key hash input or is spent to by an output. Key: 
{0x03}|{public key}
Value: 
{master key fingerprint}|{32-bit int}|...|{32-bit int}
0x04 Number of inputs provided in the PSBT None. The key must only contain the 1 byte type. A compact size unsigned integer representing the number of inputs that this PSBT has Key: 
{0x04}
Value: 
{number of inputs}

The currently defined per-input types are defined as follows:

Number Name Key Data Value Data Format Example
0x00 Non-Witness UTXO None. The key must only contain the 1 byte type. The transaction in network serialization format the current input spends from. Key: 
{0x00}
Value: 
{transaction}
0x01 Witness UTXO None. The key must only contain the 1 byte type. The entire transaction output in network serialization which the current input spends from. Key: 
{0x01}
Value: 
{serialized transaction output({output value}|<scriptPubKey>)}
0x02 Partial Signature The public key which corresponds to this signature. The signature as would be pushed to the stack from a scriptSig or witness. Key: 
{0x02}|{public key}
Value: 
{signature}
0x03 Sighash Type None. The key must only contain the 1 byte type. The 32-bit unsigned integer recommending a sighash type to be used for this input. The sighash type is only a recommendation and the signer does not need to use the sighash type specified. Key: 
{0x03}
Value: 
{sighash type}
0x04 Input index None. The key must only contain the 1 byte type. A compact size unsigned integer representing the 0-based index of this input. This field is optional to allow for completed inputs to be skipped without needing a separator byte. If one input has this type, then all inputs must have it. Key: 
{0x04}
Value: 
{input index}

The transaction format is specified as follows: 

    {0x70736274}|{0xff}|{global key-value map}|{input key-value map}|...|{input key-value map}

Field Size Name Type Value Description
4 Magic Bytes int32_t 0x70736274 Magic bytes which are ASCII for psbt. [4] This integer should be serialized in most significant byte order.
1 separator char 0xff Must be 0xff [5]
1+ Global data Key-value Map varies The key-value pairs for all global data.
1+ Inputs Array of key-value maps varies The key-value pairs for each input as described below

Each block of data between separators can be viewed as a scope, and all separators are required[6]. Types can be skipped when they are unnecessary. For example, if an input is a witness input, then it should not have a Non-Witness UTXO key-value pair.

If the signer encounters key-value pairs that it does not understand, it must pass those key-value pairs through when re-serializing the transaction.

Handling Duplicated Keys

Keys within each scope should never be duplicated; all keys in the format are unique. However implementors will still need to handle events where keys are duplicated, either duplicated in the transaction itself or when combining transactions with duplicated fields. If duplicated keys are encountered, the software may choose to use any of the values corresponding to that key.

Responsibilities

Using the transaction format involves many different responsibilities. These responsibilities can be handled by a single entity, but each responsibility is specialized in what it should be capable of doing.

Creator

The Creator must be capable of accepting either a network serialized transaction, or a PSBT. The Creator can either produce a new PSBT, or update the provided PSBT. For any scriptSigs which are non-final, the Creator will provide an empty scriptSig and input fields with information from the scriptSig, if any. If possible, the Creator should also look for any required redeemScripts and witnesScripts and add those to the global data section of the PSBT. The Creator should also provide any related UTXOs that it knows about.

Signer

The Signer must only accept a PSBT. The Signer must only use the UTXOs provided in the PSBT to produce signatures for inputs. The Signer should not need require any additional data sources, as all necessary information is provided in the PSBT format. Any signatures created by the Signer must be added as a "Partial Signature" key-value pair for the respective input it relates to.

The Signer can additionally compute the addresses and values being sent, and the transaction fee, optionally showing this data to the user as a confirmation of intent and the consequences of signing the PSBT.

Combiner

The Combiner can accept 1 or many PSBTs. The Combiner must merge them into one PSBT (if possible), or fail. The resulting PSBT must contains all of the key-value pairs from each of the PSBTs. The Combined must remove any duplicate key-value pairs, in accordance with the specification.

Finalizer

The Finalizer must only accept a PSBT. The Finalizer transforms a PSBT into a network serialized transaction.

For any inputs which are not complete, the Finalizer will emplace an empty scriptSig in the network serialized transaction. For any input which has a complete set of signatures, the Finalizer must attempt to build the complete scriptSig and encode it into the network serialized transaction.

Extensibility

The Partially Signed Transaction format can be extended in the future by adding new types for key-value pairs. Backwards compatibilty will still be maintained as those new types will be ignored and passed-through by signers which do not know about them.

Additional key-value maps with different types for the key-value pairs can be added on to the end of the format. The number of each map that follows must be specified in the globals section so that parsers will know when to use different definitions of the data types.

Compatibility

This transaction format is designed so that it is unable to be properly unserialized by normal transaction unserializers. Likewise, a normal transaction will not be able to be unserialized by an unserializer for the PSBT format.

Examples

Manual CoinJoin Workflow

2-of-3 Multisig Workflow

Test Vectors

The following test vectors are done with keys derived from the following master private key. Keypaths and individual private keys will be specified when necessary 

tprv8ZgxMBicQKsPdHrvvmuEXXZ7f5EheFqshqVmtPjeLLMjqwrWbSeuGDcgJU1icTHtLjYiGewa5zcMScbGSRR8AqB8A5wvB3XRdNYBDMhXpBS

The following are invalid PSBTs:

Test Case Explanation 
0200000001268171371edff285e937adeea4b37b78000c0566cbb3ad64641713ca42171bf6000000006a473044022070b2245123e6bf474d60c5b50c043d4c691a5d2435f09a34a7662a9dc251790a022001329ca9dacf280bdf30740ec0390422422c81cb45839457aeb76fc12edd95b3012102657d118d3357b8e0f4c2cd46db7b39f6d9c38d9a70abcb9b2de5dc8dbfe4ce31feffffff02d3dff505000000001976a914d0c59903c5bac2868760e90fd521a4665aa7652088ac00e1f5050000000017a9143545e6e33b832c47050f24d3eeb93c9c03948bc787b32e1300
 Network transaction, not PSBT format 
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
 PSBT missing null terminator 
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
 PSBT with one P2PKH input and one P2SH-P2WPKH input with only the first input signed, finalized, and skipped. Input index is specified but total input count is not given. 
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
 PSBT with one P2PKH input and one P2SH-P2WPKH input with only the first input signed, finalized, and skipped. Total input count is given but second input does not have its index.

The following are valid PSBTs:

Test Case Explanation 
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
 PSBT with one P2PKH input which has a non-final scriptSig. 
70736274ff0100750200000001268171371edff285e937adeea4b37b78000c0566cbb3ad64641713ca42171bf60000000000feffffff02d3dff505000000001976a914d0c59903c5bac2868760e90fd521a4665aa7652088ac00e1f5050000000017a9143545e6e33b832c47050f24d3eeb93c9c03948bc787b32e1300000100fda5010100000000010289a3c71eab4d20e0371bbba4cc698fa295c9463afa2e397f8533ccb62f9567e50100000017160014be18d152a9b012039daf3da7de4f53349eecb985ffffffff86f8aa43a71dff1448893a530a7237ef6b4608bbb2dd2d0171e63aec6a4890b40100000017160014fe3e9ef1a745e974d902c4355943abcb34bd5353ffffffff0200c2eb0b000000001976a91485cff1097fd9e008bb34af709c62197b38978a4888ac72fef84e2c00000017a914339725ba21efd62ac753a9bcd067d6c7a6a39d05870247304402202712be22e0270f394f568311dc7ca9a68970b8025fdd3b240229f07f8a5f3a240220018b38d7dcd314e734c9276bd6fb40f673325bc4baa144c800d2f2f02db2765c012103d2e15674941bad4a996372cb87e1856d3652606d98562fe39c5e9e7e413f210502483045022100d12b852d85dcd961d2f5f4ab660654df6eedcc794c0c33ce5cc309ffb5fce58d022067338a8e0e1725c197fb1a88af59f51e44e4255b20167c8684031c05d1f2592a01210223b72beef0965d10be0778efecd61fcac6f79a4ea169393380734464f84f2ab3000000000103040100000000
 PSBT with one P2PKH input which has a non-final scriptSig and has a sighash type specified. 
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
 PSBT with one P2PKH input and one P2SH-P2WPKH input both with non-final scriptSigs. P2SH-P2WPKH input's redeemScript is available. 
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
 PSBT with one P2PKH input and one P2SH-P2WPKH input with only the first input signed and finalized. 
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
 PSBT with one P2PKH input and one P2SH-P2WPKH input with only the first input signed, finalized, and skipped. Input indexes are used. 
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
 PSBT with one P2SH-P2WSH input of a 2-of-2 multisig, redeemScript, witnessScript, and keypaths are available. Contains one signature.

A creator with only the following:

  • Redeem Scripts:
    • 522103c8727ce35f1c93eb0be21406ee9a923c89219fe9c9e8504c8314a6a22d1295c02103c74dc710c407d7db6e041ee212d985cd2826d93f806ed44912b9a1da691c977352ae
    • 0020a8f44467bf171d51499153e01c0bd6291109fc38bd21b3c3224c9dc6b57590df
  • Witness Scripts:
    • 522102e80dec31d167865c1685e9d7a9291e66a4ea22c65cfee324289a1667ccda3b87210258cbbc3cb295a8bebac233aadc7773978804993798be5390ab444f6dd4c5327e52ae
  • UTXOs
    • TXID: 0a4381c05136c0cb44886a5df7c26f1930bcc2c12e00ec60e027c4378d7d8c2e, Index: 1
      • scriptPubKey: a914203736c3c06053896d7041ce8f5bae3df76cc49187
      • value: 0.50000000
    • TXID: 2c4df245d00b491bdf24965adbbccdaa7f62ccac933d3e9377f336c60c4ea096, Index: 0
      • scriptPubKey: a914f3ba8a120d960ae07d1dbe6f0c37fb4c926d76d587
      • value: 2.00000000
given this unsigned transaction: 
02000000022e8c7d8d37c427e060ec002ec1c2bc30196fc2f75d6a8844cbc03651c081430a0100000000ffffffff96a04e0cc636f377933e3d93accc627faacdbcdb5a9624df1b490bd045f24d2c0000000000ffffffff01e02be50e0000000017a914b53bb0dc1db8c8d803e3e39f784d42e4737ffa0d8700000000
must create this PSBT: 
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

Given the above PSBT, a signer with the following keys:

  • cQxozhqme9dcDbxT97uDu1P32Cnywc5nAMhPtQwyWhVgQnP43WGH
  • cP3ArXq5BpHE94R4buJ5uma4pyKvaWXUd5Bpsy3hS2zA69X9KMnM
must create this PSBT: 
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

Given the above blank PSBT, a signer with the following keys:

  • cUL8UxFiJjnLkkZwmmXDxmaNRQfEMDP44eZnSaiYR3KUJNv82chM
  • cNQm3eSF9rQnpoUB8xThUVDfaeRVEckPK11rGB6LjweFdhwcCS4A
must create this PSBT: 
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

Given both of the above PSBTs, a combiner must create this PSBT: 

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

Given the above PSBT, a finalizer must create this complete Bitcoin transaction: 

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

Rationale

  1. ^ Why is the separator here 0x00 instead of 0xff? The separator here is used to distinguish between each chunk of data. A separator of 0x00 would mean that the unserializer can read it as a key length of 0, which would never occur with actual keys. It can thus be used as a separator and allow for easier unserializer implementation.
  2. ^ Why are redeem scripts and witness scripts global Redeem scripts and witness scripts are global data to avoid duplication. Instead of specifying a redeems script and witness script multiple times in inputs that need those scripts, they are specified once in the global data.
  3. ^ Why are outputs' redeem scripts and witness scripts included? Redeem scripts and witness scripts spent to by an output in this transaction are included so that the user can verify that the transaction they are signing is creating the correct outputs that have the correct redeem and witness scripts. This is best used when the PSBT creator is not trusted by the signers.
  4. ^ Why use 4 bytes for psbt? The transaction format needed to start with a 5 byte header which uniquely identifies it. The first bytes were chosen to be the ASCII for psbt because that stands for Partially Signed Bitcoin Transaction.
  5. ^ Why Use a separator after the magic bytes? The separator is part of the 5 byte header for PSBT. This byte is a separator of 0xff because this will cause any non-PSBT unserializer to fail to properly unserialize the PSBT as a normal transaction. Likewise, since the 5 byte header is fixed, no transaction in the non-PSBT format will be able to be unserialized by a PSBT unserializer.
  6. ^ Why are all separators required? The separators are required so that the unserializer knows which input it is unserializing data for.

Reference implementation

The reference implementation of the PSBT format is available at https://github.com/achow101/bitcoin/tree/psbt.

Acknowledgements

Special thanks to Pieter Wuille for suggesting that such a transaction format should be made and for coming up with the name and abbreviation of PSBT.

Thanks to Pieter Wuille, Gregory Maxwell, Jonathan Underwood, and Daniel Cousens for additional comments and suggestions for improving this proposal.

Appendix A: Data types and their specifications

Any data types, their associated scope and BIP number must be defined here

Scope Type values BIP Number
Global 0,1,2,3,4 BIP 174
Input 0,1,2,3,4 BIP 174