The Multihash Data FormatProtocol Labs548 Market Street, #51207San FranciscoCA94104US+1 619 957 7606juan@protocol.aihttp://juan.benet.ai/Digital Bazaar203 Roanoke Street W.BlacksburgVA24060US+1 540 961 4469msporny@digitalbazaar.comhttp://manu.sporny.org/
Security
digest algorithmdigital signaturePKISHABLAKEposeidonskein
Cryptographic hash functions often have multiple output sizes and encodings.
This variability makes it difficult for applications to examine a series of
bytes and determine which hash function produced them. Multihash is a universal
data format for encoding outputs from hash functions. It is useful to write
applications that can simultaneously support different hash function outputs as
well as upgrade their use of hashes over time; Multihash is intended to
address these needs.
This specification is a joint work product of
Protocol Labs and the
W3C Credentials Community Group.
Feedback related to this specification should logged in the
issue tracker
or be sent to
public-credentials@w3.org.
Multihash is particularly important in systems which depend on
cryptographically secure hash functions. Attacks may break the cryptographic
properties of secure hash functions. These cryptographic breaks are
particularly painful in large tool ecosystems, where tools may have made
assumptions about hash values, such as function and digest size. Upgrading
becomes a nightmare, as all tools which make those assumptions would have
to be upgraded to use the new hash function and new hash digest length.
Tools may face serious interoperability problems or error-prone special casing.
How many programs out there assume a git hash is a SHA-1 hash?
How many scripts assume the hash value digest is exactly 160 bits?
How many tools will break when these values change?
How many programs will fail silently when these values change?
This is precisely why Multihash was created. It was designed for
seamlessly upgrading systems that depend on cryptographic hashes.
When using Multihash, a system warns the consumers of its hash values that
these may have to be upgraded in case of a break. Even though the system
may still only use a single hash function at a time, the use of multihash
makes it clear to applications that hash values may use different hash
functions or be longer in the future. Tooling, applications, and scripts
can avoid making assumptions about the length, and read it from the
multihash value instead. This way, the vast majority of tooling - which
may not do any checking of hashes - would not have to be upgraded at all.
This vastly simplifies the upgrade process, avoiding the waste of hundreds
or thousands of software engineering hours, deep frustrations, and high
blood pressure.
A multihash follows the TLV (type-length-value) pattern and consists of
several fields composed of a combination of unsigned variable length
integers and byte information.
The following section details the core data types used by the Multihash
data format.
A data type that enables one to express an unsigned integer of variable length.
When encoding an unsigned variable integer, the unsigned integer is serialized
seven bits at a time, starting with the least significant bits. The most
significant bit in each output byte indicates if there is a
continuation byte. It is not possible to express a signed integer with this
data type.
ValueEncoding (bits)hexadecimal notation1000000010x01127011111110x7F12810000000 000000010x800125511111111 000000010xFF0130010101100 000000100xAC021638410000000 10000000 000000010x808001
Implementations MUST restrict the size of the varint to a max of nine bytes
(63 bits). In order to avoid memory attacks on the encoding, the
aforementioned practical maximum length of nine bytes is used. There is
no theoretical limit, and future specs can grow this number if it is truly
necessary to have code or length values larger than 2^31.
A multihash follows the TLV (type-length-value) pattern.
The hash function identifier is an
unsigned variable integer
identifying the hash
function. The possible values for this field are provided in
The Multihash Identifier Registry.
The digest length is an
unsigned variable integer
counting the length of the digest in bytes.
The digest value is the hash function digest with a length of exactly what is
specified in the digest length, which is specified in bytes.
For example, the following is an expression of a SHA2-256 hash in hexadecimal
notation (spaces added for readability purposes):
0x12 20 41dd7b6443542e75701aa98a0c235951a28a0d851b11564d20022ab11d2589a8
The first byte (0x12) specifies the SHA2-256 hash function. The second byte
(0x20) specifies the length of the hash, which is 32 bytes. The rest of the
data specifies the value of the output of the hash function.
US Secure Hash Algorithms (SHA and SHA-based HMAC and HKDF)Federal Information Processing Standard, FIPSThe BLAKE2 Cryptographic Hash and Message Authentication Code (MAC)This document describes the cryptographic hash function BLAKE2 and makes the algorithm specification and C source code conveniently available to the Internet community. BLAKE2 comes in two main flavors: BLAKE2b is optimized for 64-bit platforms and BLAKE2s for smaller architectures. BLAKE2 can be directly keyed, making it functionally equivalent to a Message Authentication Code (MAC).MD4 to Historic StatusThis document retires RFC 1320, which documents the MD4 algorithm, and discusses the reasons for doing so. This document moves RFC 1320 to Historic status. This document is not an Internet Standards Track specification; it is published for informational purposes.MD4 to Historic StatusThis document retires RFC 1320, which documents the MD4 algorithm, and discusses the reasons for doing so. This document moves RFC 1320 to Historic status. This document is not an Internet Standards Track specification; it is published for informational purposes.
There are a number of security considerations to take into account when
implementing or utilizing this specification.
TBD
The multihash examples are chosen to show different hash functions and
different hash digest lengths at play. The input test data for all of the
examples in this section is: Merkle–Damgård
0x11148a173fd3e32c0fa78b90fe42d305f202244e2739
The fields for this multihash are - hashing function: sha1 (0x11),
length: 20 (0x14), digest: 0x8a173fd3e32c0fa78b90fe42d305f202244e2739
0x122041dd7b6443542e75701aa98a0c235951a28a0d851b11564d20022ab11d2589a8
The fields for this multihash are - hashing function: sha2-256 (0x12),
length: 32 (0x20), digest: 0x41dd7b6443542e75701aa98a0c235951a28a0d851b11564d20022ab11d2589a8
0x132052eb4dd19f1ec522859e12d89706156570f8fbab1824870bc6f8c7d235eef5f4
The fields for this multihash are - hashing function: sha2-512 (0x13),
length: 32 (0x20),
digest: 0x52eb4dd19f1ec522859e12d89706156570f8fbab1824870bc6f8c7d235eef5f4
0x134052eb4dd19f1ec522859e12d89706156570f8fbab1824870bc6f8c7d235eef5f4c2cbbafd365f96fb12b1d98a0334870c2ce90355da25e6a1108a6e17c4aaebb0
The fields for this multihash are - hashing function: sha2-512 (0x13),
length: 64 (0x40),
digest: 0x52eb4dd19f1ec522859e12d89706156570f8fbab1824870bc6f8c7d235eef5f4c2cbbafd365f96fb12b1d98a0334870c2ce90355da25e6a1108a6e17c4aaebb0
0xb24040d91ae0cb0e48022053ab0f8f0dc78d28593d0f1c13ae39c9b169c136a779f21a0496337b6f776a73c1742805c1cc15e792ddb3c92ee1fe300389456ef3dc97e2
The fields for this multihash are - hashing function: blake2b-512 (0xb240),
length: 64 (0x40),
digest: 0xd91ae0cb0e48022053ab0f8f0dc78d28593d0f1c13ae39c9b169c136a779f21a0496337b6f776a73c1742805c1cc15e792ddb3c92ee1fe300389456ef3dc97e2
0xb220207d0a1371550f3306532ff44520b649f8be05b72674e46fc24468ff74323ab030
The fields for this multihash are - hashing function: blake2b-256 (0xb220),
length: 32 (0x20),
digest: 0x7d0a1371550f3306532ff44520b649f8be05b72674e46fc24468ff74323ab030
0xb26020a96953281f3fd944a3206219fad61a40b992611b7580f1fa091935db3f7ca13d
The fields for this multihash are - hashing function: blake2s-256 (0xb260),
length: 32 (0x20),
digest: 0xa96953281f3fd944a3206219fad61a40b992611b7580f1fa091935db3f7ca13d
0xb250100a4ec6f1629e49262d7093e2f82a3278
The fields for this multihash are - hashing function: blake2s-128 (0xb250),
length: 16 (0x10), digest: 0x0a4ec6f1629e49262d7093e2f82a3278
The editors would like to thank the following individuals for feedback on and
implementations of the specification (in alphabetical order).
The Multihash Identifier Registry contains hash functions supported by Multihash
each with its canonical name, its value in hexadecimal notation, and its status.
The following initial entries should be added
to the registry to be created and maintained at (the suggested URI)
http://www.iana.org/assignments/multihash-identifiers:
NameIdentifierStatusSpecificationidentity0x00activeUnknownsha10x11activeRFC 6234sha2-2560x12activeRFC 6234sha2-5120x13activeRFC 6234sha3-5120x14activeUnknownsha3-3840x15activeUnknownsha3-2560x16activeUnknownsha3-2240x17activeUnknownshake-1280x18activeUnknownshake-2560x19activeUnknownkeccak-2240x1aactiveUnknownkeccak-2560x1bactiveUnknownkeccak-3840x1cactiveUnknownkeccak-5120x1dactiveUnknownblake30x1eactiveUnknownsha2-3840x20activeRFC 6234murmur3-x64-640x22activeUnknownmurmur3-320x23activeUnknowndbl-sha2-2560x56activeUnknownmd40xd4deprecatedRFC 6150md50xd5deprecatedRFC 6151sha2-256-trunc254-padded0x1012activeRFC 6234sha2-2240x1013activeRFC 6234sha2-512-2240x1014activeRFC 6234sha2-512-2560x1015activeRFC 6234murmur3-x64-1280x1022activeUnknownripemd-1280x1052activeUnknownripemd-1600x1053activeUnknownripemd-2560x1054activeUnknownripemd-3200x1055activeUnknownx110x1100activeUnknownkangarootwelve0x1d01activeUnknownsm3-2560x534dactiveUnknownblake2b-80xb201activeRFC 7693blake2b-160xb202activeRFC 7693blake2b-240xb203activeRFC 7693blake2b-320xb204activeRFC 7693blake2b-400xb205activeRFC 7693blake2b-480xb206activeRFC 7693blake2b-560xb207activeRFC 7693blake2b-640xb208activeRFC 7693blake2b-720xb209activeRFC 7693blake2b-800xb20aactiveRFC 7693blake2b-880xb20bactiveRFC 7693blake2b-960xb20cactiveRFC 7693blake2b-1040xb20dactiveRFC 7693blake2b-1120xb20eactiveRFC 7693blake2b-1200xb20factiveRFC 7693blake2b-1280xb210activeRFC 7693blake2b-1360xb211activeRFC 7693blake2b-1440xb212activeRFC 7693blake2b-1520xb213activeRFC 7693blake2b-1600xb214activeRFC 7693blake2b-1680xb215activeRFC 7693blake2b-1760xb216activeRFC 7693blake2b-1840xb217activeRFC 7693blake2b-1920xb218activeRFC 7693blake2b-2000xb219activeRFC 7693blake2b-2080xb21aactiveRFC 7693blake2b-2160xb21bactiveRFC 7693blake2b-2240xb21cactiveRFC 7693blake2b-2320xb21dactiveRFC 7693blake2b-2400xb21eactiveRFC 7693blake2b-2480xb21factiveRFC 7693blake2b-2560xb220activeRFC 7693blake2b-2640xb221activeRFC 7693blake2b-2720xb222activeRFC 7693blake2b-2800xb223activeRFC 7693blake2b-2880xb224activeRFC 7693blake2b-2960xb225activeRFC 7693blake2b-3040xb226activeRFC 7693blake2b-3120xb227activeRFC 7693blake2b-3200xb228activeRFC 7693blake2b-3280xb229activeRFC 7693blake2b-3360xb22aactiveRFC 7693blake2b-3440xb22bactiveRFC 7693blake2b-3520xb22cactiveRFC 7693blake2b-3600xb22dactiveRFC 7693blake2b-3680xb22eactiveRFC 7693blake2b-3760xb22factiveRFC 7693blake2b-3840xb230activeRFC 7693blake2b-3920xb231activeRFC 7693blake2b-4000xb232activeRFC 7693blake2b-4080xb233activeRFC 7693blake2b-4160xb234activeRFC 7693blake2b-4240xb235activeRFC 7693blake2b-4320xb236activeRFC 7693blake2b-4400xb237activeRFC 7693blake2b-4480xb238activeRFC 7693blake2b-4560xb239activeRFC 7693blake2b-4640xb23aactiveRFC 7693blake2b-4720xb23bactiveRFC 7693blake2b-4800xb23cactiveRFC 7693blake2b-4880xb23dactiveRFC 7693blake2b-4960xb23eactiveRFC 7693blake2b-5040xb23factiveRFC 7693blake2b-5120xb240activeRFC 7693blake2s-80xb241activeRFC 7693blake2s-160xb242activeRFC 7693blake2s-240xb243activeRFC 7693blake2s-320xb244activeRFC 7693blake2s-400xb245activeRFC 7693blake2s-480xb246activeRFC 7693blake2s-560xb247activeRFC 7693blake2s-640xb248activeRFC 7693blake2s-720xb249activeRFC 7693blake2s-800xb24aactiveRFC 7693blake2s-880xb24bactiveRFC 7693blake2s-960xb24cactiveRFC 7693blake2s-1040xb24dactiveRFC 7693blake2s-1120xb24eactiveRFC 7693blake2s-1200xb24factiveRFC 7693blake2s-1280xb250activeRFC 7693blake2s-1360xb251activeRFC 7693blake2s-1440xb252activeRFC 7693blake2s-1520xb253activeRFC 7693blake2s-1600xb254activeRFC 7693blake2s-1680xb255activeRFC 7693blake2s-1760xb256activeRFC 7693blake2s-1840xb257activeRFC 7693blake2s-1920xb258activeRFC 7693blake2s-2000xb259activeRFC 7693blake2s-2080xb25aactiveRFC 7693blake2s-2160xb25bactiveRFC 7693blake2s-2240xb25cactiveRFC 7693blake2s-2320xb25dactiveRFC 7693blake2s-2400xb25eactiveRFC 7693blake2s-2480xb25factiveRFC 7693blake2s-2560xb260activeRFC 7693skein256-80xb301activeUnknownskein256-160xb302activeUnknownskein256-240xb303activeUnknownskein256-320xb304activeUnknownskein256-400xb305activeUnknownskein256-480xb306activeUnknownskein256-560xb307activeUnknownskein256-640xb308activeUnknownskein256-720xb309activeUnknownskein256-800xb30aactiveUnknownskein256-880xb30bactiveUnknownskein256-960xb30cactiveUnknownskein256-1040xb30dactiveUnknownskein256-1120xb30eactiveUnknownskein256-1200xb30factiveUnknownskein256-1280xb310activeUnknownskein256-1360xb311activeUnknownskein256-1440xb312activeUnknownskein256-1520xb313activeUnknownskein256-1600xb314activeUnknownskein256-1680xb315activeUnknownskein256-1760xb316activeUnknownskein256-1840xb317activeUnknownskein256-1920xb318activeUnknownskein256-2000xb319activeUnknownskein256-2080xb31aactiveUnknownskein256-2160xb31bactiveUnknownskein256-2240xb31cactiveUnknownskein256-2320xb31dactiveUnknownskein256-2400xb31eactiveUnknownskein256-2480xb31factiveUnknownskein256-2560xb320activeUnknownskein512-80xb321activeUnknownskein512-160xb322activeUnknownskein512-240xb323activeUnknownskein512-320xb324activeUnknownskein512-400xb325activeUnknownskein512-480xb326activeUnknownskein512-560xb327activeUnknownskein512-640xb328activeUnknownskein512-720xb329activeUnknownskein512-800xb32aactiveUnknownskein512-880xb32bactiveUnknownskein512-960xb32cactiveUnknownskein512-1040xb32dactiveUnknownskein512-1120xb32eactiveUnknownskein512-1200xb32factiveUnknownskein512-1280xb330activeUnknownskein512-1360xb331activeUnknownskein512-1440xb332activeUnknownskein512-1520xb333activeUnknownskein512-1600xb334activeUnknownskein512-1680xb335activeUnknownskein512-1760xb336activeUnknownskein512-1840xb337activeUnknownskein512-1920xb338activeUnknownskein512-2000xb339activeUnknownskein512-2080xb33aactiveUnknownskein512-2160xb33bactiveUnknownskein512-2240xb33cactiveUnknownskein512-2320xb33dactiveUnknownskein512-2400xb33eactiveUnknownskein512-2480xb33factiveUnknownskein512-2560xb340activeUnknownskein512-2640xb341activeUnknownskein512-2720xb342activeUnknownskein512-2800xb343activeUnknownskein512-2880xb344activeUnknownskein512-2960xb345activeUnknownskein512-3040xb346activeUnknownskein512-3120xb347activeUnknownskein512-3200xb348activeUnknownskein512-3280xb349activeUnknownskein512-3360xb34aactiveUnknownskein512-3440xb34bactiveUnknownskein512-3520xb34cactiveUnknownskein512-3600xb34dactiveUnknownskein512-3680xb34eactiveUnknownskein512-3760xb34factiveUnknownskein512-3840xb350activeUnknownskein512-3920xb351activeUnknownskein512-4000xb352activeUnknownskein512-4080xb353activeUnknownskein512-4160xb354activeUnknownskein512-4240xb355activeUnknownskein512-4320xb356activeUnknownskein512-4400xb357activeUnknownskein512-4480xb358activeUnknownskein512-4560xb359activeUnknownskein512-4640xb35aactiveUnknownskein512-4720xb35bactiveUnknownskein512-4800xb35cactiveUnknownskein512-4880xb35dactiveUnknownskein512-4960xb35eactiveUnknownskein512-5040xb35factiveUnknownskein512-5120xb360activeUnknownskein1024-80xb361activeUnknownskein1024-160xb362activeUnknownskein1024-240xb363activeUnknownskein1024-320xb364activeUnknownskein1024-400xb365activeUnknownskein1024-480xb366activeUnknownskein1024-560xb367activeUnknownskein1024-640xb368activeUnknownskein1024-720xb369activeUnknownskein1024-800xb36aactiveUnknownskein1024-880xb36bactiveUnknownskein1024-960xb36cactiveUnknownskein1024-1040xb36dactiveUnknownskein1024-1120xb36eactiveUnknownskein1024-1200xb36factiveUnknownskein1024-1280xb370activeUnknownskein1024-1360xb371activeUnknownskein1024-1440xb372activeUnknownskein1024-1520xb373activeUnknownskein1024-1600xb374activeUnknownskein1024-1680xb375activeUnknownskein1024-1760xb376activeUnknownskein1024-1840xb377activeUnknownskein1024-1920xb378activeUnknownskein1024-2000xb379activeUnknownskein1024-2080xb37aactiveUnknownskein1024-2160xb37bactiveUnknownskein1024-2240xb37cactiveUnknownskein1024-2320xb37dactiveUnknownskein1024-2400xb37eactiveUnknownskein1024-2480xb37factiveUnknownskein1024-2560xb380activeUnknownskein1024-2640xb381activeUnknownskein1024-2720xb382activeUnknownskein1024-2800xb383activeUnknownskein1024-2880xb384activeUnknownskein1024-2960xb385activeUnknownskein1024-3040xb386activeUnknownskein1024-3120xb387activeUnknownskein1024-3200xb388activeUnknownskein1024-3280xb389activeUnknownskein1024-3360xb38aactiveUnknownskein1024-3440xb38bactiveUnknownskein1024-3520xb38cactiveUnknownskein1024-3600xb38dactiveUnknownskein1024-3680xb38eactiveUnknownskein1024-3760xb38factiveUnknownskein1024-3840xb390activeUnknownskein1024-3920xb391activeUnknownskein1024-4000xb392activeUnknownskein1024-4080xb393activeUnknownskein1024-4160xb394activeUnknownskein1024-4240xb395activeUnknownskein1024-4320xb396activeUnknownskein1024-4400xb397activeUnknownskein1024-4480xb398activeUnknownskein1024-4560xb399activeUnknownskein1024-4640xb39aactiveUnknownskein1024-4720xb39bactiveUnknownskein1024-4800xb39cactiveUnknownskein1024-4880xb39dactiveUnknownskein1024-4960xb39eactiveUnknownskein1024-5040xb39factiveUnknownskein1024-5120xb3a0activeUnknownskein1024-5200xb3a1activeUnknownskein1024-5280xb3a2activeUnknownskein1024-5360xb3a3activeUnknownskein1024-5440xb3a4activeUnknownskein1024-5520xb3a5activeUnknownskein1024-5600xb3a6activeUnknownskein1024-5680xb3a7activeUnknownskein1024-5760xb3a8activeUnknownskein1024-5840xb3a9activeUnknownskein1024-5920xb3aaactiveUnknownskein1024-6000xb3abactiveUnknownskein1024-6080xb3acactiveUnknownskein1024-6160xb3adactiveUnknownskein1024-6240xb3aeactiveUnknownskein1024-6320xb3afactiveUnknownskein1024-6400xb3b0activeUnknownskein1024-6480xb3b1activeUnknownskein1024-6560xb3b2activeUnknownskein1024-6640xb3b3activeUnknownskein1024-6720xb3b4activeUnknownskein1024-6800xb3b5activeUnknownskein1024-6880xb3b6activeUnknownskein1024-6960xb3b7activeUnknownskein1024-7040xb3b8activeUnknownskein1024-7120xb3b9activeUnknownskein1024-7200xb3baactiveUnknownskein1024-7280xb3bbactiveUnknownskein1024-7360xb3bcactiveUnknownskein1024-7440xb3bdactiveUnknownskein1024-7520xb3beactiveUnknownskein1024-7600xb3bfactiveUnknownskein1024-7680xb3c0activeUnknownskein1024-7760xb3c1activeUnknownskein1024-7840xb3c2activeUnknownskein1024-7920xb3c3activeUnknownskein1024-8000xb3c4activeUnknownskein1024-8080xb3c5activeUnknownskein1024-8160xb3c6activeUnknownskein1024-8240xb3c7activeUnknownskein1024-8320xb3c8activeUnknownskein1024-8400xb3c9activeUnknownskein1024-8480xb3caactiveUnknownskein1024-8560xb3cbactiveUnknownskein1024-8640xb3ccactiveUnknownskein1024-8720xb3cdactiveUnknownskein1024-8800xb3ceactiveUnknownskein1024-8880xb3cfactiveUnknownskein1024-8960xb3d0activeUnknownskein1024-9040xb3d1activeUnknownskein1024-9120xb3d2activeUnknownskein1024-9200xb3d3activeUnknownskein1024-9280xb3d4activeUnknownskein1024-9360xb3d5activeUnknownskein1024-9440xb3d6activeUnknownskein1024-9520xb3d7activeUnknownskein1024-9600xb3d8activeUnknownskein1024-9680xb3d9activeUnknownskein1024-9760xb3daactiveUnknownskein1024-9840xb3dbactiveUnknownskein1024-9920xb3dcactiveUnknownskein1024-10000xb3ddactiveUnknownskein1024-10080xb3deactiveUnknownskein1024-10160xb3dfactiveUnknownskein1024-10240xb3e0activeUnknownposeidon-bls12_381-a2-fc10xb401activeUnknownposeidon-bls12_381-a2-fc1-sc0xb402activeUnknownssz-sha2-256-bmt0xb502activeUnknown
NOTE: The most up to date place for developers to find the table above is
https://github.com/multiformats/multicodec/blob/master/table.csv.
This memo registers the "mh" digest-algorithm in the
HTTP Digest Algorithm Values
registry with the following values:
Digest Algorithm: mhDescription: The multibase-serialized value of a multihash-supported algorithm.References: this documentStatus: standard
This memo registers the "mh" hash algorithm in the
Named Information Hash Algorithm
registry with the following values:
ID: 49Hash Name String: mhValue Length: variableReference: this documentStatus: current