Network Working Group J. Benet Internet-Draft Protocol Labs Intended status: Standards Track M. Sporny Expires: February 19, 2021 Digital Bazaar August 18, 2020 The Multibase Data Format draft-multiformats-multibase-02 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 working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on February 19, 2021. Benet & Sporny Expires February 19, 2021 [Page 1] Internet-Draft The Multibase Data Format August 2020 Copyright Notice Copyright (c) 2020 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 . . . . . . . . . . . . . . . . . . . . . . . 6 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. Benet & Sporny Expires February 19, 2021 [Page 2] Internet-Draft The Multibase Data Format August 2020 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, . [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006, . 3.2. URIs [1] https://protocol.ai/ [2] https://w3c-dvcg.github.io/ Benet & Sporny Expires February 19, 2021 [Page 3] Internet-Draft The Multibase Data Format August 2020 [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): Benet & Sporny Expires February 19, 2021 [Page 4] Internet-Draft The Multibase Data Format August 2020 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]: +-------------------+-------------+--------+------------------------+ | Algorithm | Identifier | Status | Specification | | | (character) | | | +-------------------+-------------+--------+------------------------+ | identity | 0x00 | active | 8-bit binary (encoder | | | | | and decoder keeps data | | | | | unmodified) | | 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] | | | | | case-insensitive - no | | | | | padding - highest char | | base32hexupper | V | active | RFC 4648 [RFC4648] | | | | | case-insensitive - no | | | | | padding - highest char | | base32hexpad | t | active | RFC 4648 [RFC4648] | | | | | case-insensitive - | | | | | with padding | | base32hexpadupper | T | active | RFC 4648 [RFC4648] | | | | | case-insensitive - | | | | | with padding | | base32 | b | active | RFC 4648 [RFC4648] | | | | | case-insensitive - no | | | | | padding | | base32upper | B | active | RFC 4648 [RFC4648] | | | | | case-insensitive - no | | | | | padding | | base32pad | c | active | RFC 4648 [RFC4648] | | | | | case-insensitive - | | | | | with padding | | base32padupper | C | active | RFC 4648 [RFC4648] | | | | | case-insensitive - | | | | | with padding | | base32z | h | active | z-base-32 (used by | | | | | Tahoe-LAFS) | | base36 | k | active | base36 [0-9a-z] case- | | | | | insensitive - no | Benet & Sporny Expires February 19, 2021 [Page 5] Internet-Draft The Multibase Data Format August 2020 | | | | padding | | base36upper | K | active | base36 [0-9a-z] case- | | | | | insensitive - no | | | | | padding | | base58btc | z | active | base58 bitcoin | | base58flickr | Z | active | base58 flicker | | 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 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/ Benet & Sporny Expires February 19, 2021 [Page 6]