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)
|
|
|---|---|---|---|
| Last updated | 2015-10-14 | ||
| Stream | IETF | ||
| Formats | plain text pdf html bibtex | ||
| 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
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