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INTERNET-DRAFT S. Legg
draft-legg-ldap-gser-abnf-04.txt Adacel Technologies
Intended Category: Informational August 19, 2002
Common Elements of GSER Encodings
Copyright (C) The Internet Society (2002). 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 19 February 2002.
1. 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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2. Table of Contents
1. Abstract .................................................... 1
2. Table of Contents ........................................... 2
3. Introduction ................................................ 2
4. Conventions ................................................. 2
5. Separators .................................................. 2
6. ASN.1 Built-in Types ........................................ 3
7. ASN.1 Restricted String Types ............................... 7
8. Directory ASN.1 Types ....................................... 8
9. Security Considerations ..................................... 9
10. Normative References ....................................... 10
11. Informative References ..................................... 10
12. Copyright Notice ........................................... 10
13. Author's Address ........................................... 11
3. Introduction
The Generic String Encoding Rules (GSER) defined in [9] define a
human readable text encoding, based on ASN.1 [7] 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 [8] 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 [9] then [9] is to be taken as
definitive.
4. 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].
5. Separators
Certain separators are commonly used in constructing equivalent ABNF
for SET and SEQUENCE types.
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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.
6. 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-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
%x65.73.63.72.69.70.74.6F.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 = 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
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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"
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 )
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7. 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 form 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
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 ; =
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/ %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
UTCTime = dquote 10(decimal-digit) [2(decimal-digit)]
[ "Z" / u-differential ] dquote
u-differential = ( "-" / "+" ) 4(decimal-digit)
GeneralizedTime = dquote 10(decimal-digit)
*2(2(decimal-digit))
fraction [ "Z" / g-differential ] dquote
fraction = ( "." / "," ) 1*decimal-digit
g-differential = ( "-" / "+" ) 1*2(2(decimal-digit))
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
8. Directory ASN.1 Types
This section describes the GSER encoding of values of selected ASN.1
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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
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
9. Security Considerations
GSER, and therefore the ABNF encodings described in this document, do
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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.
10. 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.680 (1997) | ISO/IEC 8824-1:1998
Information Technology - Abstract Syntax Notation One (ASN.1):
Specification of basic notation
11. Informative References
[8] Wahl, M., Howes, T. and S. Kille, "Lightweight Directory Access
Protocol (v3)", RFC 2251, December 1997.
[9] Legg, S., "Generic String Encoding Rules for ASN.1 Types",
draft-legg-ldap-gser-xx.txt, a work in progress, August 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
12. Copyright Notice
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Copyright (C) The Internet Society (2002). 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
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.
13. 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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