INTERNET-DRAFT S. Legg
draft-legg-ldap-gser-abnf-00.txt Adacel Technologies
Intended Category: Informational November 12, 2001
Common Elements of GSER Encodings
Copyright (C) The Internet Society (2001). All Rights Reserved.
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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1. Abstract
The Generic String Encoding Rules (GSER) defined in Section 8 of
[CMR] define a human readable text encoding for an ASN.1 value of any
ASN.1 type. Specifications making use of GSER may wish to provide an
equivalent 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
encoding of ASN.1 types commonly occuring in LDAP syntaxes.
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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 [RFC2119].
2. Table of Contents
1. Abstract 1
2. Table of Contents 2
3. Introduction 2
4. Separators 2
5. ASN.1 Built-in Types 3
6. ASN.1 Restricted String Types 6
7. Directory ASN.1 Types 7
8. Security Considerations 8
9. References 8
10. Intellectual Property Notice 9
11. Copyright Notice 9
12. Author's Address 10
3. Introduction
The Generic String Encoding Rules (GSER) defined in Section 8 of
[CMR] define a human readable text encoding, based on ASN.1 [X680]
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 [RFC2234] 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 encoding of ASN.1 types commonly occuring in LDAP
[RFC2251] or X.500 [X500] attribute and assertion syntaxes, as well
as equivalent ABNF for the GSER encoding of 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 in [CMR] then [CMR] is to be taken as
definitive.
4. 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
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sep = [ "," ]
The <sep> rule is used in the ABNF description of the encoding of
ASN.1 SET or SEQUENCE types where all the components are 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.
5. 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.
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. The <bstring> form of
<BIT-STRING> is used otherwise. 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 hexadecimal digits is permitted.
hstring = squote *hexadecimal-digit squote %x48 ; '...'H
hexadecimal-digit = %x30-39 / ; "0" to "9"
%x41-46 ; "A" to "F"
bstring = squote *binary-digit squote %x42 ; '...'B
binary-digit = "0" / "1"
squote = %x27 ; ' (single quote)
The <BOOLEAN> rule describes the GSER encoding of values of the
BOOLEAN type.
BOOLEAN = %x54.52.55.45 / ; "TRUE"
%x46.41.4C.53.45 ; "FALSE"
The <CHARACTER-STRING> rule describes the GSER encoding of values of
the associated type for the unrestricted CHARACTER STRING type.
CHARACTER-STRING = "{" sp id-identification msp Identification ","
sp id-data-value msp OCTET-STRING
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sp "}"
id-identification = %x69.64.65.6E.74.69.66.69.63.61.74.69.6F.6E
; "identification"
id-data-value = %x64.61.74.61.2D.76.61.6C.75.65 ; "data-value"
Identification = ( id-syntaxes ":" Syntaxes ) /
( id-syntax ":" OBJECT-IDENTIFIER ) /
( id-presentation-context-id ":" INTEGER ) /
( id-context-negotiation ":" ContextNegotiation ) /
( id-transfer-syntax ":" OBJECT-IDENTIFIER ) /
( id-fixed ":" NULL )
id-syntaxes = %x73.79.6E.74.61.78.65.73 ; "syntaxes"
id-syntax = %x73.79.6E.74.61.78 ; "syntax"
id-presentation-context-id = %x70.72.65.73.65.6E.74.61.74.69.6F.6E.2D
%x63.6F.6E.74.65.78.74.2D.69.64
; "presentation-context-id"
id-context-negotiation = %x63.6F.6E.74.65.78.74.2D.6E.65.67.6F.74
%x69.61.74.69.6F.6E
; "context-negotiation"
id-transfer-syntax = %x74.72.61.6E.73.66.65.72.2D.73.79.6E.74
%x61.78 ; "transfer-syntax"
id-fixed = %x66.69.78.65.64 ; "fixed"
Syntaxes = "{" sp id-abstract msp OBJECT-IDENTIFIER ","
sp id-transfer msp OBJECT-IDENTIFIER
sp "}"
id-abstract = %x61.62.73.74.72.61.63.74 ; "abstract"
id-transfer = %x74.72.61.6E.73.66.65.72 ; "transfer"
ContextNegotiation = "{" sp id-presentation-context-id msp INTEGER ","
sp id-transfer-syntax msp OBJECT-IDENTIFIER
sp "}"
The <INTEGER> rule describes the GSER encoding of values of the
INTEGER type without a named number list. The <INTEGER-0-MAX> rule
describes the GSER encoding of values of the constrained type INTEGER
(0..MAX). The <INTEGER-1-MAX> rule describes the GSER encoding of
values of the constrained type INTEGER (1..MAX).
INTEGER = "0" / positive-number / ("-" positive-number)
INTEGER-0-MAX = "0" / positive-number
INTEGER-1-MAX = positive-number
positive-number = non-zero-digit *decimal-digit
decimal-digit = %x30-39 ; "0" to "9"
non-zero-digit = %x31-39 ; "1" to "9"
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The <EMBEDDED-PDV> rule describes the GSER encoding of values of the
associated type for the EMBEDDED PDV type.
EMBEDDED-PDV = "{" sp id-identification msp Identification
[ "," sp id-data-value-descriptor msp
ObjectDescriptor ]
"," sp id-data-value msp OCTET-STRING
sp "}"
id-data-value-descriptor = %x64.61.74.61.2D.76.61.6C.75.65.2D.64.65
%x73.63.72.69.70.74.6F.72
; "data-value-descriptor"
The <EXTERNAL> rule describes the GSER encoding of values of the
associated type for the EXTERNAL type.
EXTERNAL = "{" sp id-identification msp E-Identification
[ "," sp id-data-value-descriptor msp
ObjectDescriptor ]
"," sp id-data-value msp OCTET-STRING
sp "}"
E-Identification = ( id-syntax ":" OBJECT-IDENTIFIER ) /
( id-presentation-context-id ":" INTEGER ) /
( id-context-negotiation ":" ContextNegotiation )
The <NULL> rule describes the GSER encoding of values of the NULL
type.
NULL = %x4E.55.4C.4C ; "NULL"
The <OBJECT-IDENTIFIER> rule describes the GSER encoding of values of
the OBJECT IDENTIFIER type.
OBJECT-IDENTIFIER = oid
An OBJECT IDENTIFIER value is encoded using the string representation
described by the <oid> rule in [RFC2252]. The <oid> rule allows
either a dotted decimal representation of the OBJECT IDENTIFIER value
or an object descriptor name, i.e. <descr>. An object descriptor
name is potentially ambiguous and should be used with care.
The <OCTET-STRING> rule describes the GSER encoding of values of the
OCTET STRING type.
OCTET-STRING = hstring
The octets are encoded in order from the first octet to the last
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octet. Each octet is encoded as a pair of hexadecimal digits where
the first digit corresponds to the four most significant bits of the
octet. If the hexadecimal string does not have an even number of
digits the four least significant bits in the last octet are assumed
to be zero.
The <REAL> rule describes the GSER encoding of values of the REAL
type.
REAL = "0" / non-zero-real
non-zero-real = "{" sp id-mantissa msp INTEGER ","
sp id-base msp ( "2" / "10" ) ","
sp id-exponent msp INTEGER sp "}"
id-mantissa = %x6D.61.6E.74.69.73.73.61 ; "mantissa"
id-base = %x62.61.73.65 ; "base"
id-exponent = %x65.78.70.6F.6E.65.6E.74 ; "exponent"
6. ASN.1 Restricted String Types
This section describes the GSER encoding of values of the ASN.1
restricted character string types. The characters of a value of a
restricted character string type are encoded as a UTF8 character
string between double quotes. Any double quote characters in the
character string are escaped by being repeated.
StringValue = dquote *SafeUTF8Character dquote
dquote = %x22 ; " (double quote)
SafeUTF8Character = %x00-21 / %x23-7F / ; ASCII minus dquote
dquote dquote / ; escaped double quote
%xC0-DF %x80-BF / ; 2 byte UTF8 character
%xE0-EF 2(%x80-BF) / ; 3 byte UTF8 character
%xF0-F7 3(%x80-BF) / ; 4 byte UTF8 character
%xF8-FB 4(%x80-BF) / ; 5 byte UTF8 character
%xFC-FD 5(%x80-BF) ; 6 byte UTF8 character
The <NumericString>, <PrintableString>, <VisibleString>,
<ISO646String>, <IA5String>, <UTF8String>, <GeneralizedTime> and
<UTCTime> rules describe the GSER encoding of values of the
correspondingly named ASN.1 types. These contents of these string
types are compatible with UTF8 and do not require any translation
before being encoded. The GeneralizedTime and UTCTime types use the
VisibleString character set.
NumericString = StringValue
PrintableString = StringValue
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VisibleString = StringValue
ISO646String = StringValue
IA5String = StringValue
UTF8String = StringValue
GeneralizedTime = VisibleString
UTCTime = VisibleString
The <BMPString> and <UniversalString> rules describe the GSER
encoding of values of the BMPString and UniversalString types
respectively. BMPString (UCS-2) and UniversalString (UCS-4) values
are translated into UTF8 [RFC2279] character strings before being
encoded according to <StringValue>.
BMPString = StringValue
UniversalString = StringValue
The <TeletexString>, <T61String>, <VideotexString>, <GraphicString>,
<GeneralString> and <ObjectDescriptor> rules describe the GSER
encoding of values of the correspondingly named ASN.1 types. Values
of these string types are translated into UTF8 character strings
before being encoded according to <StringValue>. The
ObjectDescriptor type uses the GraphicString character set.
TeletexString = StringValue
T61String = StringValue
VideotexString = StringValue
GraphicString = StringValue
GeneralString = StringValue
ObjectDescriptor = GraphicString
7. Directory ASN.1 Types
This section describes the GSER encoding of values of selected ASN.1
types defined for LDAP and X.500. The ABNF rule names beginning with
uppercase letters describe the GSER encoding of values of the ASN.1
type with the same name.
AttributeType = OBJECT-IDENTIFIER
The characters of a DirectoryString are translated into UTF8
characters as required before being encoded between double quotes
with any embedded double quotes escaped by being repeated.
DirectoryString = dquote *SafeUTF8Character dquote
The <RDNSequence> rule describes the GSER encoding of values of the
RDNSequence type, which is syntactically equivalent to the
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DistinguishedName and LocalName types. The <RDNSequence> rule
encodes a name as an LDAPDN character string between double quotes.
The character string is first derived according to the
<distinguishedName> rule in Section 3 of [RFC2253], and then it is
encoded between double quotes with any embedded double quotes escaped
by being repeated.
DistinguishedName = RDNSequence
LocalName = RDNSequence
RDNSequence = dquote *SafeUTF8Character dquote
8. Security Considerations
GSER, and therefore the ABNF encodings described in this document, do
not necessarily enable the exact octet encoding of values of the
TeletexString, VideotexString, GraphicString or GeneralString types
to be reconstructed, so a transformation from DER to GSER and back to
DER may not reproduce the original DER encoding. This has
consequences for the verification of digital signatures.
9. References
[BCP-11] - R. Hovey, S. Bradner, "The Organizations Involved in the
IETF Standards Process", BCP 11, RFC 2028, October 1996.
[RFC2119] - S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119.
[RFC2234] - D. Crocker, P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[RFC2251] - M. Wahl, T. Howes, S. Kille, "Lightweight Directory
Access Protocol (v3)", RFC 2251, December 1997.
[RFC2252] - M. Wahl, A. Coulbeck, T. Howes, S. Kille, "Lightweight
Directory Access Protocol (v3): Attribute Syntax Definitions", RFC
2252, December 1997.
[RFC2253] M. Wahl, S. Kille, T. Howes. "Lightweight Directory Access
Protocol (v3): UTF-8 String Representation of Distinguished Names",
RFC2253, December 1997.
[RFC2279] - F. Yergeau, "UTF-8, a transformation format of ISO
10646", RFC 2279, January 1998.
[CMR] - S. Legg, "LDAP & X.500 Component Matching Rules", draft-legg-
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ldapext-component-matching-04.txt, November 2001.
[X500] - ITU-T Recommendation X.500 (1993) | ISO/IEC 9594-1:1994,
Information Technology - Open Systems Interconnection - The
Directory: Overview of concepts, models and services
[X680] - ITU-T Recommendation X.680 (1997) | ISO/IEC 8824-1:1998
Information Technology - Abstract Syntax Notation One (ASN.1):
Specification of basic notation
10. Intellectual Property Notice
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. [BCP-11]
Copies of claims of rights made available for publication and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementors or users of this
specification can be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
11. Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
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copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
12. Author's Address
Steven Legg
Adacel Technologies Ltd.
405-409 Ferntree Gully Road
Mount Waverley, Victoria 3149
AUSTRALIA
Phone: +61 3 9451 2107
Fax: +61 3 9541 2121
EMail: steven.legg@adacel.com.au
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