The Base16, Base32, and Base64 Data Encodings
RFC 3548
Document | Type |
RFC - Informational
(July 2003; Errata)
Obsoleted by RFC 4648
|
|
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Author | Simon Josefsson | ||
Last updated | 2020-01-21 | ||
Stream | Independent Submission | ||
Formats | plain text html pdf htmlized (tools) htmlized with errata bibtex | ||
Stream | ISE state | (None) | |
Consensus Boilerplate | Unknown | ||
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 3548 (Informational) | |
Action Holders |
(None)
|
||
Telechat date | |||
Responsible AD | Ned Freed | ||
IESG note | published 8-Jul-2003 | ||
Send notices to | <sjosefsson@rsasecurity.com> |
Network Working Group S. Josefsson, Ed. Request for Comments: 3548 July 2003 Category: Informational The Base16, Base32, and Base64 Data Encodings Status of this Memo This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved. 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, and use of different encoding alphabets. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Implementation discrepancies . . . . . . . . . . . . . . . . . 2 2.1. Line feeds in encoded data . . . . . . . . . . . . . . . 2 2.2. Padding of encoded data . . . . . . . . . . . . . . . . 3 2.3. Interpretation of non-alphabet characters in encoded data . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.4. Choosing the alphabet . . . . . . . . . . . . . . . . . 3 3. Base 64 Encoding . . . . . . . . . . . . . . . . . . . . . . . 4 4. Base 64 Encoding with URL and Filename Safe Alphabet . . . . . 6 5. Base 32 Encoding . . . . . . . . . . . . . . . . . . . . . . . 6 6. Base 16 Encoding . . . . . . . . . . . . . . . . . . . . . . . 8 7. Illustrations and examples . . . . . . . . . . . . . . . . . . 9 8. Security Considerations . . . . . . . . . . . . . . . . . . . 10 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 9.1. Normative References . . . . . . . . . . . . . . . . . . 11 9.2. Informative References . . . . . . . . . . . . . . . . . 11 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11 11. Editor's Address . . . . . . . . . . . . . . . . . . . . . . . 12 12. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 13 Josefsson Informational [Page 1] RFC 3548 The Base16, Base32, and Base64 Data Encodings July 2003 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 only US-ASCII [9] 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. MIME [3] 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. 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 RFC 2119 [1]. 2. 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. 2.1. Line feeds in encoded data MIME [3] 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 PEM [2] stating it is "virtually identical", however PEM uses a line length of 64 characters. The MIME and PEM limits are both due to limits within SMTP. Implementations MUST NOT not add line feeds to base encoded data unless the specification referring to this document explicitly directs base encoders to add line feeds after a specific number of characters. Josefsson Informational [Page 2] RFC 3548 The Base16, Base32, and Base64 Data Encodings July 2003 2.2. Padding of encoded data In some circumstances, the use of padding ("=") in base encoded data is not required nor used. In the general case, when assumptions on size of transported data cannot be made, padding is required to yield correct decoded data. Implementations MUST include appropriate pad characters at the end ofShow full document text