The Base16, Base32, and Base64 Data Encodings
RFC 4648
Document | Type |
RFC - Proposed Standard
(October 2006; Errata)
Obsoletes RFC 3548
Was draft-josefsson-rfc3548bis (individual in gen area)
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Last updated | 2015-10-14 | ||
Stream | IETF | ||
Formats | plain text pdf html bibtex | ||
Reviews | |||
Stream | WG state | (None) | |
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 4648 (Proposed Standard) | |
Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | Ted Hardie | ||
Send notices to | (None) |
Network Working Group S. Josefsson Request for Comments: 4648 SJD Obsoletes: 3548 October 2006 Category: Standards Track The Base16, Base32, and Base64 Data Encodings Status of This Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2006). Abstract This document describes the commonly used base 64, base 32, and base 16 encoding schemes. It also discusses the use of line-feeds in encoded data, use of padding in encoded data, use of non-alphabet characters in encoded data, use of different encoding alphabets, and canonical encodings. Josefsson Standards Track [Page 1] RFC 4648 Base-N Encodings October 2006 Table of Contents 1. Introduction ....................................................3 2. Conventions Used in This Document ...............................3 3. Implementation Discrepancies ....................................3 3.1. Line Feeds in Encoded Data .................................3 3.2. Padding of Encoded Data ....................................4 3.3. Interpretation of Non-Alphabet Characters in Encoded Data ..4 3.4. Choosing the Alphabet ......................................4 3.5. Canonical Encoding .........................................5 4. Base 64 Encoding ................................................5 5. Base 64 Encoding with URL and Filename Safe Alphabet ............7 6. Base 32 Encoding ................................................8 7. Base 32 Encoding with Extended Hex Alphabet ....................10 8. Base 16 Encoding ...............................................10 9. Illustrations and Examples .....................................11 10. Test Vectors ..................................................12 11. ISO C99 Implementation of Base64 ..............................14 12. Security Considerations .......................................14 13. Changes Since RFC 3548 ........................................15 14. Acknowledgements ..............................................15 15. Copying Conditions ............................................15 16. References ....................................................16 16.1. Normative References .....................................16 16.2. Informative References ...................................16 Josefsson Standards Track [Page 2] RFC 4648 Base-N Encodings October 2006 1. Introduction Base encoding of data is used in many situations to store or transfer data in environments that, perhaps for legacy reasons, are restricted to US-ASCII [1] data. Base encoding can also be used in new applications that do not have legacy restrictions, simply because it makes it possible to manipulate objects with text editors. In the past, different applications have had different requirements and thus sometimes implemented base encodings in slightly different ways. Today, protocol specifications sometimes use base encodings in general, and "base64" in particular, without a precise description or reference. Multipurpose Internet Mail Extensions (MIME) [4] is often used as a reference for base64 without considering the consequences for line-wrapping or non-alphabet characters. The purpose of this specification is to establish common alphabet and encoding considerations. This will hopefully reduce ambiguity in other documents, leading to better interoperability. 2. Conventions Used in This Document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [2]. 3. Implementation Discrepancies Here we discuss the discrepancies between base encoding implementations in the past and, where appropriate, mandate a specific recommended behavior for the future. 3.1. Line Feeds in Encoded Data MIME [4] is often used as a reference for base 64 encoding. However, MIME does not define "base 64" per se, but rather a "base 64 Content- Transfer-Encoding" for use within MIME. As such, MIME enforces a limit on line length of base 64-encoded data to 76 characters. MIME inherits the encoding from Privacy Enhanced Mail (PEM) [3], stating that it is "virtually identical"; however, PEM uses a line length ofShow full document text