Network Working Group J. Benet
Internet-Draft Protocol Labs
Intended status: Standards Track M. Sporny
Expires: July 4, 2019 Digital Bazaar
December 31, 2018
The Multibase Data Format
draft-multiformats-multibase-01
Abstract
Raw binary data is often encoded using a mechanism that enables the
data to be included in human-readable text-based formats. This
mechanism is often referred to as "base-encoding the data". Base-
encoding is often used when expressing binary data in hyperlinks,
cryptographic keys in web pages, or security tokens in application
software. There are a variety of base-encodings, such as base32,
base58, and base64. It is not always possible to differentiate one
base-encoding from another. The purpose of this specification is to
provide a mechanism to be able to deterministically identify the
base-encoding for a particular string of data.
Feedback
This specification is a joint work product of Protocol Labs [1], the
W3C Digital Verification Community Group [2], and the W3C Credentials
Community Group [3]. Feedback related to this specification should
logged in the issue tracker [4] or be sent to public-
credentials@w3.org [5]. .
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 4, 2019.
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Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. The Multibase Format . . . . . . . . . . . . . . . . . . . . 3
2.1. A Multibase Example . . . . . . . . . . . . . . . . . . . 3
3. References . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Normative References . . . . . . . . . . . . . . . . . . 3
3.2. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Appendix A. Security Considerations . . . . . . . . . . . . . . 4
Appendix B. Test Values . . . . . . . . . . . . . . . . . . . . 4
B.1. Hexadecimal upper-case encoding . . . . . . . . . . . . . 4
B.2. Base-32 upper-case encoding, no padding . . . . . . . . . 4
B.3. Base-58 Bitcoin encoding . . . . . . . . . . . . . . . . 4
B.4. Base-64 with padding and MIME-encoding . . . . . . . . . 4
Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 4
Appendix D. IANA Considerations . . . . . . . . . . . . . . . . 5
D.1. The Multibase Algorithms Registry . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
This specification describes a forward-compatible data model for
expressing raw binary data in a variety of base-encoding formats such
as base32, base58. and base64.
When text is encoded as bytes, we can usually use a one-size-fits-all
encoding (UTF-8) because we're always encoding to the same set of 256
bytes. When that doesn't work, usually for historical or performance
reasons, we can usually infer the encoding from the context.
However, when bytes are encoded as text (using a base encoding), the
choice of base encoding is often restricted by the context. Worse,
these restrictions can change based on where the data appears in the
text. In some cases, we can only use [a-z0-9]. In others, we can
use a larger set of characters but need a compact encoding. This has
lead to a large set of "base encodings", one for every use-case.
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Unlike when encoding text to bytes, we can't just standardize around
a single base encoding because there is no optimal encoding for all
cases.
Unfortunately, it's not always clear what base encoding is used;
that's where this specification comes in. It answers the question:
Given data 'd' encoded into text 's', what base is it encoded with?
2. The Multibase Format
A multibase-encoded value follows a simple format:
base-encoding-character base-encoded-data
The encoding algorithm is a single character value that is always the
first byte of the data. The possible values for this field are
provided in The Multibase Algorithm Registry [6].
2.1. A Multibase Example
The following is an encoding of "Hello World!" using the version of
base-58 that utilizes the Bitcoin encoding character set:
z2NEpo7TZRRrLZSi2U
The first byte (z) specifies the multibase encoding algorithm. The
rest of the data specifies the value of the output of the multibase
encoding algorithm.
3. References
3.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/info/rfc4648>.
3.2. URIs
[1] https://protocol.ai/
[2] https://w3c-dvcg.github.io/
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[3] https://w3c-ccg.github.io/
[4] https://github.com/w3c-dvcg/multibase/issues
[5] mailto:public-credentials@w3.org
[6] #mb-registry
[7] http://www.iana.org/assignments/multibase-algorithms
[8] https://github.com/multiformats/multibase/blob/master/
multibase.csv
Appendix A. Security Considerations
There are a number of security considerations to take into account
when implementing or utilizing this specification. TBD
Appendix B. Test Values
The multibase examples are chosen to show different encoding
algorithms and different output lengths at play. The input test data
for all of the examples in this section is:
Multibase is awesome! \o/
B.1. Hexadecimal upper-case encoding
F4D756C74696261736520697320617765736F6D6521205C6F2F
B.2. Base-32 upper-case encoding, no padding
BJV2WY5DJMJQXGZJANFZSAYLXMVZW63LFEEQFY3ZP
B.3. Base-58 Bitcoin encoding
zYAjKoNbau5KiqmHPmSxYCvn66dA1vLmwbt
B.4. Base-64 with padding and MIME-encoding
MTXVsdGliYXNlIGlzIGF3ZXNvbWUhIFxvLw==
Appendix C. Acknowledgements
The editors would like to thank the following individuals for
feedback on and implementations of the specification (in alphabetical
order):
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Appendix D. IANA Considerations
D.1. The Multibase Algorithms Registry
The following initial entries should be added to the Multibase
Algorithms Registry to be created and maintained at (the suggested
URI) http://www.iana.org/assignments/multibase-algorithms [7]:
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+-------------------+-------------+--------+------------------------+
| Algorithm | Identifier | Status | Specification |
| | (character) | | |
+-------------------+-------------+--------+------------------------+
| identity | 0x00 | active | 8-bit binary (encoder |
| | | | and decoder keeps data |
| | | | unmodified) |
| base1 | 1 | active | unary (11111) |
| base2 | 0 | active | binary (01010101) |
| base8 | 7 | active | octal |
| base10 | 9 | active | decimal |
| base16 | f | active | hexadecimal |
| base16upper | F | active | hexadecimal |
| base32hex | v | active | RFC 4648 [RFC4648] no |
| | | | padding - highest char |
| base32hexupper | V | active | RFC 4648 [RFC4648] no |
| | | | padding - highest char |
| base32hexpad | t | active | RFC 4648 [RFC4648] |
| | | | with padding |
| base32hexpadupper | T | active | RFC 4648 [RFC4648] |
| | | | with padding |
| base32 | b | active | RFC 4648 [RFC4648] no |
| | | | padding |
| base32upper | B | active | RFC 4648 [RFC4648] no |
| | | | padding |
| base32pad | c | active | RFC 4648 [RFC4648] |
| | | | with padding |
| base32padupper | C | active | RFC 4648 [RFC4648] |
| | | | with padding |
| base32z | h | active | z-base-32 (used by |
| | | | Tahoe-LAFS) |
| base58flickr | Z | active | base58 flicker |
| base58btc | z | active | base58 bitcoin |
| base64 | m | active | RFC 4648 [RFC4648] no |
| | | | padding |
| base64pad | M | active | RFC 4648 [RFC4648] |
| | | | with padding - MIME |
| | | | encoding |
| base64url | u | active | RFC 4648 [RFC4648] no |
| | | | padding |
| base64urlpad | U | active | RFC 4648 [RFC4648] |
| | | | with padding |
+-------------------+-------------+--------+------------------------+
Table 1: Multihash Algorithms Registry
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NOTE: The most up to date place for developers to find the table
above is https://github.com/multiformats/multibase/blob/master/
multibase.csv [8].
Authors' Addresses
Juan Benet
Protocol Labs
548 Market Street, #51207
San Francisco, CA 94104
US
Phone: +1 619 957 7606
Email: juan@protocol.ai
URI: http://juan.benet.ai/
Manu Sporny
Digital Bazaar
203 Roanoke Street W.
Blacksburg, VA 24060
US
Phone: +1 540 961 4469
Email: msporny@digitalbazaar.com
URI: http://manu.sporny.org/
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