Common Elements of Generic String Encoding Rules (GSER) Encodings
RFC 3642

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Network Working Group                                            S. Legg
Request for Comments: 3642                           Adacel Technologies
Category: Informational                                     October 2003

   Common Elements of Generic String Encoding Rules (GSER) 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

   The Generic String Encoding Rules (GSER) describe a human readable
   text encoding for an Abstract Syntax Notation One (ASN.1) value of
   any ASN.1 type.  Specifications making use of GSER may wish to
   provide an equivalent Augmented Backus-Naur Form (ABNF) description
   of the GSER encoding for a particular ASN.1 type as a convenience for
   implementors.  This document supports such specifications by
   providing equivalent ABNF for the GSER encodings for ASN.1 types that
   commonly occur in Lightweight Directory Access Protocol (LDAP)
   syntaxes.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2.  Conventions. . . . . . . . . . . . . . . . . . . . . . . . . .  2
   3.  Separators . . . . . . . . . . . . . . . . . . . . . . . . . .  2
   4.  ASN.1 Built-in Types . . . . . . . . . . . . . . . . . . . . .  2
   5.  ASN.1 Restricted String Types. . . . . . . . . . . . . . . . .  7
   6.  Directory ASN.1 Types. . . . . . . . . . . . . . . . . . . . .  9
   7.  Security Considerations. . . . . . . . . . . . . . . . . . . . 10
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
       8.1.  Normative References . . . . . . . . . . . . . . . . . . 10
       8.2.  Informative References . . . . . . . . . . . . . . . . . 11
   9.  Intellectual Property Notice . . . . . . . . . . . . . . . . . 12
   10. Author's Address . . . . . . . . . . . . . . . . . . . . . . . 12
   11. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 13

Legg                         Informational                      [Page 1]
RFC 3642           Common Elements of GSER Encodings        October 2003

1.  Introduction

   The Generic String Encoding Rules (GSER) [7] define a human readable
   text encoding, based on ASN.1 [8] value notation, for an ASN.1 value
   of any ASN.1 type.  Specifications making use of GSER may wish to
   provide a non-normative equivalent ABNF [3] description of the GSER
   encoding for a particular ASN.1 type as a convenience for
   implementors unfamiliar with ASN.1.  This document supports such
   specifications by providing equivalent ABNF for the GSER encodings
   for ASN.1 types that commonly occur in LDAP [10] or X.500 [11]
   attribute and assertion syntaxes, as well as equivalent ABNF for the
   GSER encodings for the ASN.1 built-in types.

   The ABNF given in this document does not replace or alter GSER in any
   way.  If there is a discrepancy between the ABNF specified here and
   the encoding defined by GSER [7], then GSER is to be taken as
   definitive.

2.  Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", and "MAY" in this document are
   to be interpreted as described in BCP 14, RFC 2119 [1].  The key word
   "OPTIONAL" is exclusively used with its ASN.1 meaning.

3.  Separators

   Certain separators are commonly used in constructing equivalent ABNF
   for SET and SEQUENCE types.

      sp  =  *%x20  ; zero, one or more space characters
      msp = 1*%x20  ; one or more space characters

      sep = [ "," ]

   The <sep> rule is used in the ABNF description of the encoding for
   ASN.1 SET or SEQUENCE types where all the components are either
   OPTIONAL or DEFAULT.  It encodes to an empty string if and only if
   the immediately preceding character in the encoding is "{", i.e., it
   is only empty for the first optional component actually present in
   the SET or SEQUENCE value being encoded.

4.  ASN.1 Built-in Types

   This section describes the GSER encoding of values of the ASN.1
   built-in types, except for the restricted character string types.

Legg                         Informational                      [Page 2]
RFC 3642           Common Elements of GSER Encodings        October 2003

   The <BIT-STRING> rule describes the GSER encoding of values of the
   BIT STRING type without a named bit list.

      BIT-STRING = bstring / hstring

   If the number of bits in a BIT STRING value is a multiple of four the
   <hstring> form of <BIT-STRING> MAY be used.  Otherwise, the <bstring>
   form of <BIT-STRING> is used.  The <bstring> rule encodes each bit as
   the character "0" or "1" in order from the first bit to the last bit.
   The <hstring> rule encodes each group of four bits as a hexadecimal
   number where the first bit is the most significant.  An odd number of