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INTERNET-DRAFT S. Legg
draft-legg-ldap-gser-abnf-06.txt Adacel Technologies
Intended Category: Informational May 7, 2003
Common Elements of GSER Encodings
Copyright (C) The Internet Society (2003). 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.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as
Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress".
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Distribution of this document is unlimited. Comments should be sent
to the LDAPEXT working group mailing list <ietf-ldapext@netscape.com>
or to the author.
This Internet-Draft expires on 7 November 2003.
Abstract
The Generic String Encoding Rules (GSER) describe 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 encodings for ASN.1 types
commonly occuring in Lightweight Directory Access Protocol (LDAP)
syntaxes.
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1. Table of Contents
1. Table of Contents ............................................. 2
2. Introduction .................................................. 2
3. Conventions ................................................... 2
4. Separators .................................................... 2
5. ASN.1 Built-in Types .......................................... 3
6. ASN.1 Restricted String Types ................................. 7
7. Directory ASN.1 Types ......................................... 9
8. Security Considerations ....................................... 10
9. Normative References .......................................... 11
10. Informative References ....................................... 11
11. Copyright Notice ............................................. 11
12. Author's Address ............................................. 12
2. Introduction
The Generic String Encoding Rules (GSER) defined in [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 commonly occuring in LDAP [9] or X.500 [10] 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 in [7] then [7] is to be taken as
definitive.
3. Conventions
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].
4. Separators
Certain separators are commonly used in constructing equivalent ABNF
for SET and SEQUENCE types.
sp = *%x20 ; zero, one or more space characters
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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.
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.
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CHARACTER-STRING = "{" sp id-identification msp Identification ","
sp id-data-value msp OCTET-STRING
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
%x2D.63.6F.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
%x74.69.61.74.69.6F.6E
; "context-negotiation"
id-transfer-syntax = %x74.72.61.6E.73.66.65.72.2D.73.79.6E
%x74.61.78 ; "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)
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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"
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 msp OCTET-STRING
sp "}"
The <EXTERNAL> rule describes the GSER encoding of values of the
associated type for the EXTERNAL type.
EXTERNAL = "{" [ sp id-direct-reference msp
OBJECT-IDENTIFIER "," ]
[ sp id-indirect-reference msp INTEGER "," ]
[ sp id-data-value-descriptor msp
ObjectDescriptor "," ]
sp id-encoding msp Encoding
sp "}"
id-direct-reference = %x64.69.72.65.63.74.2D.72.65.66.65.72
%x65.6E.63.65
; "direct-reference"
id-indirect-reference = %x69.6E.64.69.72.65.63.74.2D.72.65.66
%x65.72.65.6E.63.65
; "indirect-reference"
id-data-value-descriptor = %x64.61.74.61.2D.76.61.6C.75.65.2D.64
%x65.73.63.72.69.70.74.6F.72
; "data-value-descriptor"
id-encoding = %x65.6E.63.6F.64.69.6E.67
; "encoding"
Encoding = ( id-single-ASN1-type ":" Value ) /
( id-octet-aligned ":" OCTET-STRING ) /
( id-arbitrary ":" BIT-STRING )
id-single-ASN1-type = %x73.69.6E.67.6C.65.2D.41.53.4E.31.2D.74.79
%x70.65
; "single-ASN1-type"
id-octet-aligned = %x6F.63.74.65.74.2D.61.6C.69.67.6E.65.64
; "octet-aligned"
id-arbitrary = %x61.72.62.69.74.72.61.72.79
; "arbitrary"
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The <Value> rule is defined in [7]. It represents the GSER encoding
of a single value of the ASN.1 type identified by the direct-
reference and/or indirect-reference components.
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 = numeric-oid / descr
numeric-oid = oid-component 1*( "." oid-component )
oid-component = "0" / positive-number
An OBJECT IDENTIFIER value is encoded using either the dotted decimal
representation or an object descriptor name, i.e. <descr>. The
<descr> rule is described in [4]. 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
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" ; zero
/ PLUS-INFINITY ; positive infinity
/ MINUS-INFINITY ; negative infinity
/ realnumber ; positive base 10 REAL value
/ ( "-" realnumber ) ; negative base 10 REAL value
/ real-sequence-value ; non-zero base 2 or 10 REAL value
PLUS-INFINITY = %x50.4C.55.53.2D.49.4E.46.49.4E.49.54.59
; "PLUS-INFINITY"
MINUS-INFINITY = %x4D.49.4E.55.53.2D.49.4E.46.49.4E.49.54.59
; "MINUS-INFINITY"
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realnumber = mantissa exponent
mantissa = (positive-number [ "." *decimal-digit ])
/ ( "0." *("0") positive-number )
exponent = "E" ( "0" / ([ "-" ] positive-number))
real-sequence-value = "{" 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"
A value of the REAL type MUST be encoded as "0" if it is zero.
The <RELATIVE-OID> rule describes the GSER encoding of values of the
RELATIVE-OID type.
RELATIVE-OID = oid-component *( "." oid-component )
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 always encoded as a UTF8
character string between double quotes. For some of the ASN.1 string
types this requires a translation to or from the UTF8 encoding. Some
of the ASN.1 string types permit only a subset of the characters
representable in UTF8. Any double quote characters in the character
string, where allowed by the character set, are escaped by being
repeated.
The <UTF8String> rule describes the GSER encoding of values of the
UTF8String type. The characters of this string type do not require
any translation before being encoded.
UTF8String = StringValue
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
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The <NumericString>, <PrintableString>, <VisibleString>,
<ISO646String>, <IA5String>, <GeneralizedTime> and <UTCTime> rules
describe the GSER encoding of values of the correspondingly named
ASN.1 types. The characters 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, but have a strictly defined format.
NumericString = dquote *(decimal-digit / space) dquote
space = %x20
PrintableString = dquote *PrintableCharacter dquote
PrintableCharacter = decimal-digit / space
/ %x41-5A ; A to Z
/ %x61-7A ; a to z
/ %x27-29 ; ' ( )
/ %x2B-2F ; + , - . /
/ %x3A ; :
/ %x3D ; =
/ %x3F ; ?
ISO646String = VisibleString
VisibleString = dquote *SafeVisibleCharacter dquote
SafeVisibleCharacter = %x20-21
/ %x23-7E ; printable ASCII minus dquote
/ dquote dquote ; escaped double quote
IA5String = dquote *SafeIA5Character dquote
SafeIA5Character = %x00-21 / %x23-7F ; ASCII minus dquote
/ dquote dquote ; escaped double quote
century = 2(%x30-39) ; "00" to "99"
year = 2(%x30-39) ; "00" to "99"
month = ( %x30 %x31-39 ) ; "01" (January) to "09"
/ ( %x31 %x30-32 ) ; "10" to "12"
day = ( %x30 %x31-39 ) ; "01" to "09"
/ ( %x31-32 %x30-39 ) ; "10" to "29"
/ ( %x32 %x30-31 ) ; "30" to "31"
hour = ( %x30-31 %x30-39 ) / ( %x32 %x30-33 ) ; "00" to "23"
minute = %x30-36 %x30-39 ; "00" to "59"
second = %x30-36 %x30-39 ; "00" to "59"
UTCTime = dquote year month day hour minute [ second ]
[ %x5A / u-differential ] dquote
u-differential = ( "-" / "+" ) hour minute
GeneralizedTime = dquote century year month day hour
[ minute [ second ] ] [ fraction ]
[ %x5A / g-differential ] dquote
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fraction = ( "." / "," ) 1*(%x30-39)
g-differential = ( "-" / "+" ) hour [ minute ]
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 [6] 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 = StringValue /
( id-teletexString ":" TeletexString ) /
( id-printableString ":" PrintableString ) /
( id-bmpString ":" BMPString ) /
( id-universalString ":" UniversalString ) /
( id-uTF8String ":" UTF8String )
id-teletexString = %x74.65.6C.65.74.65.78.53.74.72.69.6E.67
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; "teletexString"
id-printableString = %x70.72.69.6E.74.61.62.6C.65
%x53.74.72.69.6E.67 ; "printableString"
id-bmpString = %x62.6D.70.53.74.72.69.6E.67 ; "bmpString"
id-universalString = %x75.6E.69.76.65.72.73.61.6C
%x53.74.72.69.6E.67 ; "universalString"
id-uTF8String = %x75.54.46.38.53.74.72.69.6E.67
; "uTF8String"
The <RDNSequence> rule describes the GSER encoding of values of the
RDNSequence type, which is syntactically equivalent to the
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 [5], 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
The <RelativeDistinguishedName> rule describes the GSER encoding of
values of the RelativeDistinguishedName type that are not part of an
RDNSequence value. The <RelativeDistinguishedName> rule encodes an
RDN as a double quoted string containing the RDN as it would appear
in an LDAPDN character string. The character string is first derived
according to the <name-component> rule in Section 3 of [6], and then
any embedded double quote characters are escaped by being repeated.
This resulting string is output between double quotes.
RelativeDistinguishedName = dquote *SafeUTF8Character dquote
The <ORAddress> rule encodes an X.400 address as an IA5 character
string between double quotes. The character string is first derived
according to Section 4.1 of [2], and then any embedded double quotes
are escaped by being repeated. This resulting string is output
between double quotes.
ORAddress = dquote *SafeIA5Character dquote
8. Security Considerations
This document contains an alternative description of parts of the
Generic String Encoding Rules, but does not replace or alter GSER in
any way. For the full security implications of using GSER see the
Security Considerations section of [7].
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9. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Kille, S., "MIXER (Mime Internet X.400 Enhanced Relay): Mapping
between X.400 and RFC 822/MIME", RFC 2156, January 1998.
[3] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[4] Wahl, M., Coulbeck, A., Howes, T. and S. Kille, "Lightweight
Directory Access Protocol (v3): Attribute Syntax Definitions",
RFC 2252, December 1997.
[5] Wahl, M., Kille, S. and T. Howes, "Lightweight Directory Access
Protocol (v3): UTF-8 String Representation of Distinguished
Names", RFC 2253, December 1997.
[6] Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC
2279, January 1998.
[7] Legg, S., "Generic String Encoding Rules for ASN.1 Types",
draft-legg-ldap-gser-xx.txt, a work in progress, May 2003.
[8] ITU-T Recommendation X.680 (1997) | ISO/IEC 8824-1:1998
Information Technology - Abstract Syntax Notation One (ASN.1):
Specification of basic notation
10. Informative References
[9] Hodges, J. and R. Morgan, "Lightweight Directory Access Protocol
(v3): Technical Specification", RFC 3377, September 2002.
[10] ITU-T Recommendation X.500 (1993) | ISO/IEC 9594-1:1994,
Information Technology - Open Systems Interconnection - The
Directory: Overview of concepts, models and services
11. Copyright Notice
Copyright (C) The Internet Society (2003). 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
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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
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.
250 Bay Street
Brighton, Victoria 3186
AUSTRALIA
Phone: +61 3 8530 7710
Fax: +61 3 8530 7888
EMail: steven.legg@adacel.com.au
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INTERNET-DRAFT S. Legg
draft-legg-ldap-gser-03.txt Adacel Technologies
Intended Category: Standard Track May 7, 2003
Generic String Encoding Rules for ASN.1 Types
Copyright (C) The Internet Society (2003). 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.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as
Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress".
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Distribution of this document is unlimited. Comments should be sent
to the LDAPEXT working group mailing list <ietf-ldapext@netscape.com>
or to the author.
This Internet-Draft expires on 7 November 2003.
Abstract
This document defines a set of Abstract Syntax Notation One (ASN.1)
encoding rules, called the Generic String Encoding Rules, that
produce a human readable text encoding for values of any given ASN.1
data type.
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1. Table of Contents
1. Table of Contents ............................................. 2
2. Introduction .................................................. 2
3. Conventions ................................................... 3
4. Generic String Encoding Rules ................................. 3
4.1 Type Referencing Notations ................................ 4
4.2 Restricted Character String Types ......................... 4
4.3 ChoiceOfStrings Types ..................................... 5
4.4 Identifiers ............................................... 7
4.5 BIT STRING ................................................ 7
4.6 BOOLEAN ................................................... 8
4.7 ENUMERATED ................................................ 8
4.8 INTEGER ................................................... 8
4.9 NULL ...................................................... 8
4.10 OBJECT IDENTIFIER and RELATIVE-OID ....................... 9
4.11 OCTET STRING ............................................. 9
4.12 CHOICE ................................................... 9
4.13 SEQUENCE and SET ......................................... 10
4.14 SEQUENCE OF and SET OF ................................... 11
4.15 CHARACTER STRING ......................................... 11
4.16 EMBEDDED PDV ............................................. 11
4.17 EXTERNAL ................................................. 11
4.18 INSTANCE OF .............................................. 12
4.19 REAL ..................................................... 12
4.20 Variant Encodings ........................................ 12
5. GSER Transfer Syntax .......................................... 13
6. Security Considerations ....................................... 13
7. Normative References .......................................... 14
8. Informative References ........................................ 15
9. Copyright Notice .............................................. 15
10. Author's Address ............................................. 16
2. Introduction
This document defines a set of ASN.1 [8] encoding rules, called the
Generic String Encoding Rules or GSER, that produce a human readable
UTF8 [6] character string encoding of ASN.1 values of any given
arbitrary ASN.1 type.
Note that "ASN.1 value" does not mean a BER [13] encoded value. The
ASN.1 value is an abstract concept that is independent of any
particular encoding. BER is just one possible encoding of an ASN.1
value.
GSER is based on ASN.1 value notation [8], with changes to
accommodate the notation's use as a transfer syntax, and to support
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well established ad-hoc string encodings for LDAP [14] directory data
types.
Though primarily intended for defining the LDAP-specific encoding of
new LDAP attribute syntaxes and assertion syntaxes, these encoding
rules could also be used in other domains where human readable
renderings of ASN.1 values would be useful.
Referencing the Generic String Encoding Rules (GSER) is sufficient to
define a human readable text encoding for values of a specific ASN.1
type, however other specifications may wish to provide a customized
ABNF [3] description, independent of the ASN.1, as a convenience for
the implementor (equivalent ABNF for the GSER encodings for ASN.1
types commonly occuring in LDAP syntaxes is provided in [15]). Such
a specification SHOULD state that if there is a discrepancy between
the customized ABNF and the GSER encoding defined by this document,
that the GSER encoding takes precedence.
3. Conventions
Throughout this document "type" shall be taken to mean an ASN.1 type,
and "value" shall be taken to mean an ASN.1 value.
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].
4. Generic String Encoding Rules
The GSER encoding of a value of any ASN.1 type is described by the
following ABNF [3]:
Value = BitStringValue /
BooleanValue /
CharacterStringValue /
ChoiceValue /
EmbeddedPDVValue /
EnumeratedValue /
ExternalValue /
GeneralizedTimeValue /
IntegerValue /
InstanceOfValue /
NullValue /
ObjectDescriptorValue /
ObjectIdentifierValue /
OctetStringValue /
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RealValue /
RelativeOIDValue /
SequenceOfValue /
SequenceValue /
SetOfValue /
SetValue /
StringValue /
UTCTimeValue /
VariantEncoding
The ABNF for each of the above rules is given in the following
sections.
4.1 Type Referencing Notations
A value of a type with a defined type name is encoded according to
the type definition on the right hand side of the type assignment for
the type name.
A value of a type denoted by the use of a parameterized type with
actual parameters is encoded according to the parameterized type with
the DummyReferences [12] substituted with the actual parameters.
A value of a tagged or constrained type is encoded as a value of the
type without the tag or constraint, respectively. Tags do not appear
in the string encodings defined by this document. See [8] and [11]
for the details of ASN.1 constraint notation.
A value of an open type denoted by an ObjectClassFieldType (Clause 14
of [10]) is encoded according to the specific type of the value.
A value of a fixed type denoted by an ObjectClassFieldType is encoded
according to that fixed type.
A value of a selection type is encoded according to the type
referenced by the selection type.
A value of a type described by TypeFromObject notation (Clause 15 of
[10]) is encoded according to the denoted type.
A value of a type described by ValueSetFromObjects notation (Clause
15 of [10]) is encoded according to the governing type.
4.2 Restricted Character String Types
The contents of a string value are encoded as a UTF8 character string
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between double quotes, regardless of the ASN.1 string type.
Depending on the ASN.1 string type, and an application's internal
representation of that string type, a translation to or from the UTF8
character encoding may be required. NumericString, PrintableString,
IA5String, VisibleString (ISO646String) are compatible with UTF8 and
do not require any translation. BMPString (UCS-2) and
UniversalString (UCS-4) have a direct mapping to and from UTF8 [6].
For the remaining string types see [8]. Any embedded double quotes
in the resulting UTF8 character string are escaped by repeating the
double quote characters.
A value of the NumericString, PrintableString, TeletexString
(T61String), VideotexString, IA5String, GraphicString, VisibleString
(ISO646String), GeneralString, BMPString, UniversalString or
UTF8String type is encoded according to the <StringValue> rule.
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
A value of the GeneralizedTime type, UTCTime type or ObjectDescriptor
type is encoded as a string value. GeneralizedTime and UTCTime use
the VisibleString character set so the conversion to UTF8 is trivial.
ObjectDescriptor uses the GraphicString type.
GeneralizedTimeValue = StringValue
UTCTimeValue = StringValue
ObjectDescriptorValue = StringValue
4.3 ChoiceOfStrings Types
It is not uncommon for ASN.1 specifications to define types that are
a CHOICE between two or more alternative ASN.1 string types, where
the particular alternative chosen carries no semantic significance
(DirectoryString [7] being a prime example). Such types are defined
to avoid having to use a complicated character encoding for all
values when most values could use a simpler string type, or to deal
with evolving requirements that compel the use of a broader character
set while still maintaining backward compatibility.
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GSER encodes values of all the ASN.1 string types as UTF8 character
strings so the alternative chosen in a purely syntactic CHOICE of
string types makes no material difference to the final encoding of
the string value.
While there are certain ASN.1 constructs that betray the semantic
significance of the alternatives within a CHOICE type, the absence of
those constructs does not necessarily mean a CHOICE type is purely
syntactic. Therefore, it is necessary for specifications to declare
the purely syntactic CHOICE types so that they may be more compactly
encoded (see Section 4.12). These declared CHOICE types are referred
to as ChoiceOfStrings types.
To be eligible to be declared a ChoiceOfStrings type an ASN.1 type
MUST satisfy the following conditions.
a) The type is a CHOICE type.
b) The component type of each alternative is one of the following
ASN.1 restricted string types: NumericString, PrintableString,
TeletexString (T61String), VideotexString, IA5String,
GraphicString, VisibleString (ISO646String), GeneralString,
BMPString, UniversalString or UTF8String.
c) All the alternatives are of different restricted string types,
i.e. no two alternatives have the same ASN.1 restricted string
type.
d) Either none of the alternatives has a constraint, or all of the
alternatives have exactly the same constraint.
Tagging on the alternative types is ignored.
Consider the ASN.1 parameterized type definition of DirectoryString.
DirectoryString { INTEGER : maxSize } ::= CHOICE {
teletexString TeletexString (SIZE (1..maxSize)),
printableString PrintableString (SIZE (1..maxSize)),
bmpString BMPString (SIZE (1..maxSize)),
universalString UniversalString (SIZE (1..maxSize)),
uTF8String UTF8String (SIZE (1..maxSize)) }
Any use of the DirectoryString parameterized type with an actual
parameter defines a ASN.1 type that satisfies the above conditions.
Recognising that the alternative within a DirectoryString carries no
semantic significance, this document declares (each and every use of)
DirectoryString{} to be a ChoiceOfStrings type.
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Other specifications MAY declare other types satisfying the above
conditions to be ChoiceOfStrings types. The declaration SHOULD be
made at the point where the ASN.1 type is defined, otherwise it
SHOULD be made at the point where it is introduced as, or in, an LDAP
attribute or assertion syntax.
4.4 Identifiers
An <identifier> conforms to the definition of an identifier in ASN.1
notation (Clause 11.3 of [8]). It begins with a lowercase letter and
is followed by zero or more letters, digits, and hyphens. A hyphen
is not permitted to be the last character and a hyphen is not
permitted to be followed by another hyphen. The case of letters in
an identifier is always significant.
identifier = lowercase *alphanumeric *(hyphen 1*alphanumeric)
alphanumeric = uppercase / lowercase / decimal-digit
uppercase = %x41-5A ; "A" to "Z"
lowercase = %x61-7A ; "a" to "z"
decimal-digit = %x30-39 ; "0" to "9"
hyphen = "-"
4.5 BIT STRING
A value of the BIT STRING type is encoded according to the
<BitStringValue> rule. If the definition of the BIT STRING type
includes a named bit list, the <bit-list> form of <BitStringValue>
MAY be used. If the number of bits in a BIT STRING value is a
multiple of four the <hstring> form of <BitStringValue> MAY be used.
The <bstring> form of <BitStringValue> is used otherwise.
BitStringValue = bstring / hstring / bit-list
The <bit-list> rule encodes the one bits in the bit string value as a
comma separated list of identifiers. Each <identifier> MUST be one
of those in the named bit list. An <identifier> MUST NOT appear more
than once in the same <bit-list>. 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.
bit-list = "{" [ sp identifier
*( "," sp identifier ) ] sp "}"
hstring = squote *hexadecimal-digit squote %x48 ; '...'H
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hexadecimal-digit = %x30-39 / ; "0" to "9"
%x41-46 ; "A" to "F"
bstring = squote *binary-digit squote %x42 ; '...'B
binary-digit = "0" / "1"
sp = *%x20 ; zero, one or more space characters
squote = %x27 ; ' (single quote)
4.6 BOOLEAN
A value of the BOOLEAN type is encoded according to the
<BooleanValue> rule.
BooleanValue = %x54.52.55.45 / ; "TRUE"
%x46.41.4C.53.45 ; "FALSE"
4.7 ENUMERATED
A value of the ENUMERATED type is encoded according to the
<EnumeratedValue> rule. The <identifier> MUST be one of those in the
list of enumerations in the definition of the ENUMERATED type.
EnumeratedValue = identifier
4.8 INTEGER
A value of the INTEGER type is encoded according to the
<IntegerValue> rule. If the definition of the INTEGER type includes
a named number list, the <identifier> form of <IntegerValue> MAY be
used, in which case the <identifier> MUST be one of those in the
named number list.
IntegerValue = "0" /
positive-number /
("-" positive-number) /
identifier
positive-number = non-zero-digit *decimal-digit
non-zero-digit = %x31-39 ; "1" to "9"
4.9 NULL
A value of the NULL type is encoded according to the <NullValue>
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rule.
NullValue = %x4E.55.4C.4C ; "NULL"
4.10 OBJECT IDENTIFIER and RELATIVE-OID
A value of the OBJECT IDENTIFIER type is encoded according to the
<ObjectIdentifierValue> rule. The <ObjectIdentifierValue> rule
allows either a dotted decimal representation of the OBJECT
IDENTIFIER value or an object descriptor name, i.e. <descr>. The
<descr> rule is described in [4]. An object descriptor name is
potentially ambiguous and should be used with care.
ObjectIdentifierValue = numeric-oid / descr
numeric-oid = oid-component 1*( "." oid-component )
oid-component = "0" / positive-number
A value of the RELATIVE-OID [9] type is encoded according to the
<RelativeOIDValue> rule.
RelativeOIDValue = oid-component *( "." oid-component )
4.11 OCTET STRING
A value of the OCTET STRING type is encoded according to the
<OctetStringValue> rule. The octets are encoded in order from the
first octet to the last 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.
OctetStringValue = hstring
4.12 CHOICE
A value of a CHOICE type is encoded according to the <ChoiceValue>
rule. The <ChoiceOfStringsValue> encoding MAY be used if the
corresponding CHOICE type has been declared a ChoiceOfStrings type.
This document declares DirectoryString to be a ChoiceOfStrings type
(see Section 4.3). The <IdentifiedChoiceValue> form of <ChoiceValue>
is used otherwise.
ChoiceValue = IdentifiedChoiceValue /
ChoiceOfStringsValue
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IdentifiedChoiceValue = identifier ":" Value
ChoiceOfStringsValue = StringValue
For implementations that recognise the internal structure of the
DirectoryString CHOICE type (e.g. X.500 directories [16]), if the
character string between the quotes in a <StringValue> contains only
characters that are permitted in a PrintableString the
DirectoryString is assumed to use the printableString alternative,
otherwise it is assumed to use the uTF8String alternative. The
<IdentifiedChoiceValue> rule MAY be used for a value of type
DirectoryString to indicate a different alternative to the one that
would otherwise be assumed from the string contents. No matter what
alternative is chosen, the <Value> will still be a UTF8 encoded
character string, however it is a syntax error if the characters in
the UTF8 string cannot be represented in the string type of the
chosen alternative.
Implementations that don't care about the internal structure of a
DirectoryString value MUST be able to parse the
<IdentifiedChoiceValue> form for a DirectoryString value, though the
particular identifier found will be of no interest.
4.13 SEQUENCE and SET
A value of a SEQUENCE type is encoded according to the
<SequenceValue> rule. The <ComponentList> rule encodes a comma
separated list of the particular component values present in the
SEQUENCE value, where each component value is preceded by the
corresponding identifier from the SEQUENCE type definition. The
components are encoded in the order of their definition in the
SEQUENCE type.
SequenceValue = ComponentList
ComponentList = "{" [ sp NamedValue *( "," sp NamedValue) ] sp "}"
NamedValue = identifier msp Value
msp = 1*%x20 ; one or more space characters
A value of a SET type is encoded according to the <SetValue> rule.
The components are encoded in the order of their definition in
the SET type (i.e. just like a SEQUENCE value).
This is a deliberate departure from ASN.1 value notation where
the components of a SET can be written in any order.
SetValue = ComponentList
SEQUENCE and SET type definitions are sometimes extended by the
inclusion of additional component types, so an implementation SHOULD
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be capable of skipping over any <NamedValue> encoding with an
identifier that is not recognised, on the assumption that the sender
is using a more recent definition of the SEQUENCE or SET type.
4.14 SEQUENCE OF and SET OF
A value of a SEQUENCE OF type is encoded according to the
<SequenceOfValue> rule, as a comma separated list of the instances in
the value. Each instance is encoded according to the component type
of the SEQUENCE OF type.
SequenceOfValue = "{" [ sp Value *( "," sp Value) ] sp "}"
A value of a SET OF type is encoded according to the <SetOfValue>
rule, as a list of the instances in the value. Each instance is
encoded according to the component type of the SET OF type.
SetOfValue = "{" [ sp Value *( "," sp Value) ] sp "}"
4.15 CHARACTER STRING
A value of the unrestricted CHARACTER STRING type is encoded
according to the corresponding SEQUENCE type defined in Clause 39.5
of [8] (see [15] for equivalent ABNF).
CharacterStringValue = SequenceValue
4.16 EMBEDDED PDV
A value of the EMBEDDED PDV type is encoded according to the
corresponding SEQUENCE type defined in Clause 32.5 of [8] (see [15]
for equivalent ABNF).
EmbeddedPDVValue = SequenceValue
4.17 EXTERNAL
A value of the EXTERNAL type is encoded according to the
corresponding SEQUENCE type defined in Clause 8.18.1 of [13] (see
[15] for equivalent ABNF).
ExternalValue = SequenceValue
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4.18 INSTANCE OF
A value of the INSTANCE OF type is encoded according to the
corresponding SEQUENCE type defined in Annex C of [10].
InstanceOfValue = SequenceValue
4.19 REAL
A value of the REAL type MUST be encoded as "0" if it is zero,
otherwise it is encoded as either the special value <PLUS-INFINITY>,
the special value <MINUS-INFINITY>, an optionally signed <realnumber>
(based on the extended value notation for REAL from [17]) or as a
value of the corresponding SEQUENCE type for REAL defined in Clause
20.5 of [8] (see [15] for equivalent ABNF).
RealValue = "0" ; zero REAL value
/ PLUS-INFINITY ; positive infinity
/ MINUS-INFINITY ; negative infinity
/ realnumber ; positive base 10 REAL value
/ "-" realnumber ; negative base 10 REAL value
/ SequenceValue ; non-zero REAL value, base 2 or 10
realnumber = mantissa exponent
mantissa = (positive-number [ "." *decimal-digit ])
/ ( "0." *("0") positive-number )
exponent = "E" ( "0" / ([ "-" ] positive-number))
PLUS-INFINITY = %x50.4C.55.53.2D.49.4E.46.49.4E.49.54.59
; "PLUS-INFINITY"
MINUS-INFINITY = %x4D.49.4E.55.53.2D.49.4E.46.49.4E.49.54.59
; "MINUS-INFINITY"
4.20 Variant Encodings
The values of some named complex ASN.1 types have special string
encodings. These special encodings are always used instead of the
encoding that would otherwise apply based on the ASN.1 type
definition.
VariantEncoding = RDNSequenceValue /
RelativeDistinguishedNameValue /
ORAddressValue
A value of the RDNSequence type, i.e. a distinguished name, is
encoded according to the <RDNSequenceValue> rule, as a quoted LDAPDN
character string. The character string is first derived according to
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the <distinguishedName> rule in Section 3 of [5], and then it is
encoded as if it were a UTF8String value, i.e. between double quotes
with any embedded double quotes escaped by being repeated.
RDNSequenceValue = StringValue
A RelativeDistinguishedName value that is not part of an RDNSequence
value is encoded according to the <RelativeDistinguishedNameValue>
rule as a quoted character string. The character string is first
derived according to the <name-component> rule in Section 3 of [5],
and then it is encoded as if it were a UTF8String value.
RelativeDistinguishedNameValue = StringValue
A value of the ORAddress type is encoded according to the
<ORAddressValue> rule as a quoted character string. The character
string is first derived according to the textual representation of
MTS.ORAddress from [2], and then it is encoded as if it were an
IA5String value.
ORAddressValue = StringValue
5. GSER Transfer Syntax
The following OBJECT IDENTIFIER has been assigned to identify the
Generic String Encoding Rules:
{ 1 2 36 79672281 0 0 }
This OBJECT IDENTIFIER would be used, for example, to describe the
transfer syntax for a GSER encoded data-value in an EMBEDDED PDV
value.
6. Security Considerations
The Generic String Encoding Rules do not define a canonical encoding.
That is, a transformation from a GSER encoding into some other
encoding (e.g. BER) and back into GSER will not necessarily reproduce
exactly the original GSER octet encoding. Therefore GSER SHOULD NOT
be used where a canonical encoding is needed.
Furthermore, GSER does 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. Therefore GSER SHOULD NOT be used where
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reversibility to DER is needed, e.g. for the verification of digital
signatures. Instead, DER or a DER-reversible encoding should be
used.
When interpreting security-sensitive fields, and in particular fields
used to grant or deny access, implementations MUST ensure that any
comparisons are done on the underlying abstract value, regardless of
the particular encoding used.
7. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Kille, S., "MIXER (Mime Internet X.400 Enhanced Relay): Mapping
between X.400 and RFC 822/MIME", RFC 2156, January 1998.
[3] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[4] Wahl, M., Coulbeck, A., Howes, T. and S. Kille, "Lightweight
Directory Access Protocol (v3): Attribute Syntax Definitions",
RFC 2252, December 1997.
[5] Wahl, M., Kille S. and T. Howes. "Lightweight Directory Access
Protocol (v3): UTF-8 String Representation of Distinguished
Names", RFC 2253, December 1997.
[6] Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC
2279, January 1998.
[7] ITU-T Recommendation X.520 (1993) | ISO/IEC 9594-6:1994,
Information Technology - Open Systems Interconnection - The
Directory: Selected attribute types
[8] ITU-T Recommendation X.680 (1997) | ISO/IEC 8824-1:1998
Information Technology - Abstract Syntax Notation One (ASN.1):
Specification of basic notation
[9] ITU-T Recommendation X.680 - Amendment 1 (06/99) | ISO/IEC
8824-1:1998/Amd 1:2000 Relative object identifiers
[10] ITU-T Recommendation X.681 (1997) | ISO/IEC 8824-2:1998
Information Technology - Abstract Syntax Notation One (ASN.1):
Information object specification
[11] ITU-T Recommendation X.682 (1997) | ISO/IEC 8824-3:1998
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Information Technology - Abstract Syntax Notation One (ASN.1):
Constraint specification
[12] ITU-T Recommendation X.683 (1997) | ISO/IEC 8824-4:1998
Information Technology - Abstract Syntax Notation One (ASN.1):
Parameterization of ASN.1 specifications
[13] ITU-T Recommendation X.690 (1997) | ISO/IEC 8825-1:1998
Information Technology - ASN.1 encoding rules: Specification of
Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and
Distinguished Encoding Rules (DER)
8. Informative References
[14] Hodges, J. and R. Morgan, "Lightweight Directory Access
Protocol (v3): Technical Specification", RFC 3377, September
2002.
[15] Legg, S., "Common Elements of GSER Encodings",
draft-legg-ldap-gser-abnf-xx.txt, a work in progress, May 2003.
[16] ITU-T Recommendation X.500 (1993) | ISO/IEC 9594-1:1994,
Information Technology - Open Systems Interconnection - The
Directory: Overview of concepts, models and services
[17] ITU-T Recommendation X.680 - Corrigendum 3 (02/2001)
9. Copyright Notice
Copyright (C) The Internet Society (2003). 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
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
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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.
10. Author's Address
Steven Legg
Adacel Technologies Ltd.
250 Bay Street
Brighton, Victoria 3186
AUSTRALIA
Phone: +61 3 8530 7710
Fax: +61 3 8530 7888
EMail: steven.legg@adacel.com.au
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Internet-Draft Editor: J. Sermersheim
Intended Category: Experimental Novell, Inc
Document: draft-sermersheim-ldap-csn-00.txt Dec 2003
The LDAP Change Sequence Number Syntax and Matching Rules
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that other
groups may also distribute working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Distribution of this memo is unlimited. Technical discussion of this
document will take place on the IETF LDAP
Duplication/Replication/Update Protocols (ldup) mailing list <ietf-
ldup@imc.org>. Please send editorial comments directly to the editor
<jimse@novell.com>.
Abstract
This document defines a syntax schema element for the Lightweight
Directory Access Protocol ([LDAP]) which is used to hold a Change
Sequence Number (CSN). In general, a change sequence number
represents the place and time that a directory entity was changed. It
may be used by various attributes for various LDAP replication, and
synchronization applications.
Table of Contents
1. Introduction....................................................2
2. Conventions.....................................................2
3. Syntaxes........................................................2
3.1 ChangeSequenceNumber Syntax....................................2
3.2 UTF8String.....................................................3
4. Matching Rules..................................................3
4.1 changeSequenceNumberMatch Matching Rule........................3
Sermersheim Internet-Draft - Expires Jun 2004 Page 1
LDAP Change Sequence Number
4.2 utf8CodePointMatch Matching Rule...............................4
4.3 changeSequenceNumberOrderingMatch Matching Rule................4
4.4 utf8CodePointOrderingMatch Matching Rule.......................4
5. Security Considerations.........................................5
6. Acknowledgements................................................5
7. Normative References............................................5
8. Informative References..........................................6
9. IANA Considerations.............................................6
10. Editor's Address...............................................6
1. Introduction
A number of technologies have been documented, implemented and
experimented with which in one way or another seek to replicate, or
synchronize directory data. A common need among these technologies is
to determine which of two copies of an element represents the latest
or most authoritative data. Part of meeting this need involves
associating a change sequence number to an element copy at the time
of an update to that element. When replication or synchronization
occurs, the change sequence numbers associated with directory
elements can be used to decide which element's data will be copied to
the other element(s).
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 [Keyword].
The General Considerations in Section 3.1 of [Syntaxes] apply to the
syntax definition in this document.
The terms "directory element" and "element" refer to data held in a
directory and may apply to an attribute value, attribute, entry, or
any other identifiable directory entity.
3. Syntaxes
3.1 ChangeSequenceNumber Syntax
A value of the ChangeSequenceNumber syntax is the time of a change
along with a replicaID which represents the Directory System Agent
(DSA) holding the element when it was changed. There are also two
sequence numbers used to disambiguate directory entities that are
changed at the same time and place.
The Abstract Syntax Notation One ([ASN.1]) type corresponding to this
syntax is defined as follows:
ChangeSequenceNumber ::= SEQUENCE {
time GeneralizedTime,
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timeCount INTEGER (0 .. MaxInt),
replicaID UTF8String,
changeCount INTEGER (0 .. MaxInt)}
MaxInt INTEGER ::= 2147483647 -- (2^^31 - 1) --
GeneralizedTime is defined in [ASN.1]. Local time without a
differential SHALL NOT be used.
UTF8String is defined below.
The LDAP-specific encoding of a value of this syntax is the Generic
String Encoding Rules ([GSER]) encoding of the ASN.1 type.
Example:
{ time "196701160315-0700",
timeCount 0,
replicaID "DSA666",
changeCount 1 }
The following is an LDAP syntax description [RFC2252] suitable for
publication in the subschema.
( IANA-ASSIGNED-OID.1 DESC 'ChangeSequenceNumber' )
3.2 UTF8String
The UTF8String syntax is used to express a string of characters from
the [ISO10646] character set (a superset of [Unicode]), encoded
following the [UTF-8] algorithm. Note that Unicode characters U+0000
through U+007F are the same as ASCII 0 through 127, respectively, and
have the same single octet UTF-8 encoding. Other Unicode characters
have a multiple octet UTF-8 encoding.
UTF8String::= OCTET STRING -- UTF-8 encoded,
-- [ISO10646] characters
The LDAP-specific encoding of a value of this syntax are the UTF-8
characters themselves.
The following is an LDAP syntax description [RFC2252] suitable for
publication in the subschema.
( IANA-ASSIGNED-OID.2 DESC 'UTF8String')
4. Matching Rules
4.1 changeSequenceNumberMatch Matching Rule
The changeSequenceNumberMatch rule compares an assertion value of the
ChangeSequenceNumber syntax to a value of a syntax (e.g the
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LDAP Change Sequence Number
ChangeSequenceNumber syntax) whose corresponding ASN.1 type is
ChangeSequenceNumber.
The rule evaluates to TRUE if and only if each of the components of
the two values evaluate to true using the following rules:
- The time component uses generalizedTimeMatch.
- The timeCount and changeCount components use integerMatch.
- The replicaID component uses utf8CodePointMatch.
The following is a LDAP matching rule description [RFC2252] suitable
for publication in the subschema.
( IANA-ASSIGNED-OID.3 NAME changeSequenceNumberMatch
SYNTAX IANA-ASSIGNED-OID.1 )
4.2 utf8CodePointMatch Matching Rule
The utf8CodePointMatch rule compares an assertion value of the
UTF8String syntax to a value of a syntax (e.g the UTF8String syntax)
whose corresponding ASN.1 type is UTF8String. The rule evaluates to
TRUE if and only if the code points [Unicode] of each of the
characters is equal.
The following is a LDAP matching rule description [RFC2252] suitable
for publication in the subschema.
( IANA-ASSIGNED-OID.4 NAME utf8CodePointMatch
SYNTAX IANA-ASSIGNED-OID.2 )
4.3 changeSequenceNumberOrderingMatch Matching Rule
The changeSequenceNumberOrderingMatch rule compares the
ChangeSequenceNumber ordering of an assertion value of the
ChangeSequenceNumber syntax to a value of a syntax (e.g the
ChangeSequenceNumber syntax) whose corresponding ASN.1 type is
ChangeSequenceNumber.
The rule evaluates to TRUE if and only if each of the components of
the two values evaluate to true using the following rules:
- The time component uses GeneralizedTimeOrderingMatch.
- The timeCount and changeCount components use integerOrderingMatch.
- The replicaID component uses utf8CodePointOrderingMatch.
The following is a LDAP matching rule description [RFC2252] suitable
for publication in the subschema.
( IANA-ASSIGNED-OID.5 NAME changeSequenceNumberOrderingMatch
SYNTAX SYNTAX IANA-ASSIGNED-OID.1 )
4.4 utf8CodePointOrderingMatch Matching Rule
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LDAP Change Sequence Number
The utf8CodePointOrderingMatch rule compares the ordering of an
assertion value of the UTF8String syntax to a stored value of a
syntax (e.g the UTF8String syntax) whose corresponding ASN.1 type is
UTF8String.
The rule evaluates to TRUE if, and only if, in the code point
collation order, the stored value character string appears earlier
than the assertion value character string, i.e., the stored value is
"less than" the assertion value.
The following is a LDAP matching rule description [RFC2252] suitable
for publication in the subschema.
( IANA-ASSIGNED-OID.6 NAME utf8CodePointOrderingMatch
SYNTAX IANA-ASSIGNED-OID.2 )
5. Security Considerations
6. Acknowledgements
7. Normative References
[ABNF] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[ASN.1] ITU-T Recommendation X.680 (07/2002) | ISO/IEC 8824-1:2002
"Information Technology - Abstract Syntax Notation One
(ASN.1): Specification of basic notation"
[Keyword] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
[Syntaxes] Legg, S., and K. Dally, "LDAP: Syntaxes and Matching
Rules", draft-ietf-ldapbis-syntaxes-xx.txt, (a work in
progress).
[Models] Zeilenga, K., "LDAP: Directory Information Models", draft-
ietf-ldapbis-models-xx.txt (a work in progress).
[ISO10646] Universal Multiple-Octet Coded Character Set (UCS) -
Architecture and Basic Multilingual Plane, ISO/IEC 10646-1
: 1993.
[Unicode] The Unicode Consortium, "The Unicode Standard, Version
3.2.0" is defined by "The Unicode Standard, Version 3.0"
(Reading, MA, Addison-Wesley, 2000. ISBN 0-201-61633-5),
as amended by the "Unicode Standard Annex #27: Unicode
3.1" (http://www.unicode.org/reports/tr27/) and by the
"Unicode Standard Annex #28: Unicode 3.2"
(http://www.unicode.org/reports/tr28/).
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[RFC2252] Wahl, M., Coulbeck, A., Howes, T. and S. Kille,
"Lightweight Directory Access Protocol (v3): Attribute
Syntax Definitions", RFC 2252, December 1997.
8. Informative References
9. IANA Considerations
10. Editor's Address
Jim Sermersheim
Novell, Inc.
1800 South Novell Place
Provo, Utah 84606, USA
jimse@novell.com
+1 801 861-3088
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LDAP Change Sequence Number
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