{"number":391,"title":"Binary Output Descriptors","authors":["SeedHammer"],"status":"Closed","type":"Specification","layer":"Applications","created":"2026-01-27","license":"BSD-2-Clause","requires":[],"replaces":[],"replacedBy":[393],"discussion":[],"abstract":"This document proposes an efficient container format for encoding an output descriptor as defined by BIP 380 and its extensions. Based on key-value maps as defined by BIP 174 , the encoding supports descriptor and key metadata.","eli5":"Proposes a compact binary format for storing and transferring output descriptors, the text descriptions of a wallet's addresses. It can also carry extra information about the descriptor and its keys, making it suitable for QR codes, hardware devices, and other space-constrained uses.","categories":["wallets"],"filename":"bip-0391.mediawiki","githubUrl":"https://github.com/bitcoin/bips/blob/master/bip-0391.mediawiki","format":"mediawiki","readingMinutes":5,"inbound":0,"revisions":1,"impact":0,"core":false,"references":[174,380,389],"lastModified":"2026-04-23","html":"

Introduction

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Abstract

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This document proposes an efficient container format for encoding an output descriptor as defined by BIP 380 and its extensions. Based on key-value maps as defined by BIP 174, the encoding supports descriptor and key metadata.

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Copyright

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

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Motivation

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A BIP 380 output descriptor is a textual representation of a set of output scripts, such that Bitcoin wallets may agree on the scripts and addresses to provide the user. However, a descriptor string by itself is not ideal for transferring between wallets: it lacks a machine-recognizable header, cannot represent metadata such as name and birth block, and its use of base58 for extended keys is inefficient.

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BIP 174 gives us a self-describing file format, metadata, and a compact, binary representation of keys. Assuming most wallets already implement the PSBT format, the implementation overhead of this BIP is expected to be low [1] [2] Why not use the new Blockchain Commons BCR-2023-010 format? The BCR-2023-010 format is roughly equivalent to this proposal, but was designed and released outside of the usual BIP proposal process.

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In particular, we believe BCR-2023-010 would have faced opposition in the BIP process because it is based on the CBOR encoding. CBOR is designed for generality and compactness and is therefore significantly more complex than the PSBT encoding. In contrast, the PSBT key-value maps are supported by all wallet software that interact with PSBT files, are easier to review, and they fit in embedded devices.

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Released in late 2023, BCR-2023-010 doesn't have the advantage of widespread support at the time of this writing..

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Specification

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The Binary Output Descriptor (BOD) format consists of a fixed header, a key-value map describing the output descriptor, and a key-value map for each key.

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<bod> := <magic> <global-map> <key-map>*\n<magic> := 0x62 0x6F 0x64 0xFF\n<global-map> := <keypair>* 0x00\n<key-map> := <keypair>* 0x00
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The definition for <keypair> follows BIP 174.

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The defined global types are as follows:

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Name<keytype><keydata><keydata> Description<valuedata><valuedata> Description
Output DescriptorBOD_GLOBAL_OUTPUT_DESCRIPTOR = 0x00<compact size uint birth block><bytes>The earliest block height that may contain transactions for the descriptor, optionally followed by the UTF-8 encoded name of the descriptor.<bytes descriptor>The output descriptor in BIP 380 format without inline keys[3].
Proprietary Use TypeBOD_GLOBAL_PROPRIETARY = 0xFC<compact size uint identifier length> <bytes identifier> <compact size uint subtype> <bytes subkeydata>A compact size unsigned integer of the length of the identifier, followed by an identifier prefix, followed by a compact size unsigned integer subtype, followed by the key data itself.<bytes data>Any value data as defined by the proprietary type user.
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It is an error to omit the BOD_GLOBAL_OUTPUT_DESCRIPTOR entry.

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All key expressions in the BOD_GLOBAL_OUTPUT_DESCRIPTOR descriptor string must be specified as references in the form of @<index> where index is the 0-based index into the ordered list of <key-map> entries. An index out of range is invalid.

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A BOD_GLOBAL_OUTPUT_DESCRIPTOR with inline keys is invalid[4][5].

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Key references may be followed by derivation paths as specified in BIP 389.

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The defined key types are as follows:

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Name<keytype><keydata><keydata> Description<valuedata><valuedata> Description
Extended Public KeyBOD_KEY_XPUB = 0x00<bytes xpub>The 78-byte serialized extended public key, as defined by BIP 32.<4 byte fingerprint> <32-bit little endian uint path element>*The master key fingerprint, as defined by BIP 32, concatenated with the derivation path of the public key. The derivation path is represented as 32-bit little endian unsigned integer indexes concatenated with each other. The number of 32-bit unsigned integer indexes must match the depth provided in the extended public key.
Proprietary Use TypeBOD_KEY_PROPRIETARY = 0xFC<compact size uint identifier length> <bytes identifier> <compact size uint subtype> <bytes subkeydata>A compact size unsigned integer of the length of the identifier, followed by an identifier prefix, followed by a compact size unsigned integer subtype, followed by the key data itself.<bytes data>Any value data as defined by the proprietary type user.
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Test Vectors

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Invalid Cases

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A descriptor with a key reference out of bounds.

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Descriptor: wpkh(@0/*)\nHex encoded BOD: 70736274ff0207000a77706b682840302f2a29000000
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A descriptor with an invalid UTF-8 name.

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Hex-encoded BOD: 70736274ff05070061c57a0a77706b682840302f2a2953010488b21e041c0ae906800000025afed56d755c088320ec9bc6acd84d33737b580083759e0a0ff8f26e429e0b77028342f5f7773f6fab374e1c2d3ccdba26bc0933fc4f63828b662b4357e4cc3791bec0fbd814c5d8729748000080000000800000008002000080000000
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A descriptor with an inline key. Hex-encoded BOD: 70736274ff0207008e77706b68285b64633536373237362f3438682f30682f30682f32685d7870756236446959726652774e6e6a655834764873574d616a4a56464b726245456e753867415739764475517a675457457345484531367347576558585556314c42575145317943546d657072534e63715a3357373468715664674462745948557633654d3457325445556870616e2f2a29000000

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Valid Cases

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A 2-of-3 multisig descriptor

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Descriptor: wsh(sortedmulti(2,@0/<0;1>/*,@1/<0;1>/*,@2/<0;1>/*))\nName: Satoshi's Stash\nBirth block: 123456789012345\nKey 0: [dc567276/48h/0h/0h/2h]xpub6DiYrfRwNnjeX4vHsWMajJVFKrbEEnu8gAW9vDuQzgTWEsEHE16sGWeXXUV1LBWQE1yCTmeprSNcqZ3W74hqVdgDbtYHUv3eM4W2TEUhpan\nKey 1: [f245ae38/48h/0h/0h/2h]xpub6DnT4E1fT8VxuAZW29avMjr5i99aYTHBp9d7fiLnpL5t4JEprQqPMbTw7k7rh5tZZ2F5g8PJpssqrZoebzBChaiJrmEvWwUTEMAbHsY39Ge\nKey 2: [c5d87297/48h/0h/0h/2h]xpub6DjrnfAyuonMaboEb3ZQZzhQ2ZEgaKV2r64BFmqymZqJqviLTe1JzMr2X2RfQF892RH7MyYUbcy77R7pPu1P71xoj8cDUMNhAMGYzKR4noZ\nHex-encoded BOD: 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Rationale

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  1. Why not extend BIP 174? The PSBT format is not a general-purpose container format, and descriptors are useful outside of signing flows (backup, initializing wallet software). ↩
  2. Why not use the older Blockchain Commons BCR-2020-010 format? The format was recently deprecated, due to its use of reserved CBOR tags. ↩
  3. Why not encode the descriptor in binary?\nDesigning and maintaining a compact binary representation of the complex and evolving BIP 380 descriptor\nlanguage entail significant effort and introduce a time lag from the introduction of new BIP 380 features\nto the specification of the binary counterpart. We don't believe the space savings outweigh the disadvantages.\n\nThe major source of bloat, base58-encoded keys, are binary encoded for compactness and\ncan be re-used multiple times in a single descriptor.\n ↩
  4. Why not allow inline keys? Allowing inline keys risks incompatible implementations that omit parsing of referenced keys. ↩
  5. What about named pk(NAME) references? Named references would allow Miniscript descriptors as-is in BOD_GLOBAL_OUTPUT_DESCRIPTOR. They are left out because they complicate decoders and can trivially be replaced by indexed references. ↩
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Compatibility

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This is a new format and as such has no compatibility burden.

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Reference Implementation

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There is a Go implementation for development and testing purposes. Don't use it in production, because it only validates the BOD format, not the descriptor itself.

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Changelog

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Acknowledgments

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This specification builds upon the draft BIP 388 by specifying a serialization format for compact descriptors. It also uses the indexed key references from that BIP, as well as examples and test vectors.

","toc":[{"id":"introduction","title":"Introduction","level":2},{"id":"abstract","title":"Abstract","level":3},{"id":"copyright","title":"Copyright","level":3},{"id":"motivation","title":"Motivation","level":3},{"id":"specification","title":"Specification","level":2},{"id":"test-vectors","title":"Test Vectors","level":2},{"id":"invalid-cases","title":"Invalid Cases","level":3},{"id":"valid-cases","title":"Valid Cases","level":3},{"id":"rationale","title":"Rationale","level":2},{"id":"compatibility","title":"Compatibility","level":2},{"id":"reference-implementation","title":"Reference Implementation","level":2},{"id":"changelog","title":"Changelog","level":2},{"id":"acknowledgments","title":"Acknowledgments","level":2}],"history":{"totalCommits":1,"firstCommit":"2026-04-23T20:17:01+02:00","lastUpdated":"2026-04-23T20:17:01+02:00","events":[{"sha":"9eb67f5764763746fcfd8aedd205bb9f4a6590a6","date":"2026-04-23T20:17:01+02:00","author":"SeedHammer","message":"Merge pull request #1548 from seedhammer/master","url":"https://github.com/bitcoin/bips/commit/9eb67f5764763746fcfd8aedd205bb9f4a6590a6","kind":"edit"}]}}