Network Working Group K. Zeilenga
Request for Comments: 4013 OpenLDAP Foundation
Category: Standards Track February 2005
SASLprep: Stringprep Profile for User Names and Passwords
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 (C) The Internet Society (2005).
This document describes how to prepare Unicode strings representing
user names and passwords for comparison. The document defines the
"SASLprep" profile of the "stringprep" algorithm to be used for both
user names and passwords. This profile is intended to be used by
Simple Authentication and Security Layer (SASL) mechanisms (such as
PLAIN, CRAM-MD5, and DIGEST-MD5), as well as other protocols
exchanging simple user names and/or passwords.
The use of simple user names and passwords in authentication and
authorization is pervasive on the Internet. To increase the
likelihood that user name and password input and comparison work in
ways that make sense for typical users throughout the world, this
document defines rules for preparing internationalized user names and
passwords for comparison. For simplicity and implementation ease, a
single algorithm is defined for both user names and passwords.
The algorithm assumes all strings are comprised of characters from
the Unicode [Unicode] character set.
This document defines the "SASLprep" profile of the "stringprep"
The profile is designed for use in Simple Authentication and Security
Layer ([SASL]) mechanisms, such as [PLAIN], [CRAM-MD5], and
[DIGEST-MD5]. It may be applicable where simple user names and
Zeilenga Standards Track [Page 1]RFC 4013 SASLprep February 2005
passwords are used. This profile is not intended for use in
preparing identity strings that are not simple user names (e.g.,
email addresses, domain names, distinguished names), or where
identity or password strings that are not character data, or require
different handling (e.g., case folding).
This document does not alter the technical specification of any
existing protocols. Any specification that wishes to use the
algorithm described in this document needs to explicitly incorporate
this document and provide precise details as to where and how this
algorithm is used by implementations of that specification.
2. The SASLprep Profile
This section defines the "SASLprep" profile of the "stringprep"
algorithm [StringPrep]. This profile is intended for use in
preparing strings representing simple user names and passwords.
This profile uses Unicode 3.2 [Unicode].
Character names in this document use the notation for code points and
names from the Unicode Standard [Unicode]. For example, the letter
"a" may be represented as either <U+0061> or <LATIN SMALL LETTER A>.
In the lists of mappings and the prohibited characters, the "U+" is
left off to make the lists easier to read. The comments for
character ranges are shown in square brackets (such as "[CONTROL
CHARACTERS]") and do not come from the standard.
Note: A glossary of terms used in Unicode can be found in [Glossary].
Information on the Unicode character encoding model can be found in
This profile specifies:
- non-ASCII space characters [StringPrep, C.1.2] that can be
mapped to SPACE (U+0020), and
- the "commonly mapped to nothing" characters [StringPrep, B.1]
that can be mapped to nothing.
This profile specifies using Unicode normalization form KC, as
described in Section 4 of [StringPrep].
Zeilenga Standards Track [Page 2]RFC 4013 SASLprep February 20052.3. Prohibited Output
This profile specifies the following characters as prohibited input:
- Non-ASCII space characters [StringPrep, C.1.2]
- ASCII control characters [StringPrep, C.2.1]
- Non-ASCII control characters [StringPrep, C.2.2]