mirror of
https://git.openldap.org/openldap/openldap.git
synced 2024-12-21 03:10:25 +08:00
900 lines
32 KiB
Plaintext
900 lines
32 KiB
Plaintext
|
||
|
||
|
||
|
||
|
||
|
||
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.
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
Legg Expires 7 November 2003 [Page 1]
|
||
|
||
INTERNET-DRAFT Generic String Encoding Rules May 7, 2003
|
||
|
||
|
||
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
|
||
|
||
|
||
|
||
Legg Expires 7 November 2003 [Page 2]
|
||
|
||
INTERNET-DRAFT Generic String Encoding Rules May 7, 2003
|
||
|
||
|
||
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 /
|
||
|
||
|
||
|
||
Legg Expires 7 November 2003 [Page 3]
|
||
|
||
INTERNET-DRAFT Generic String Encoding Rules May 7, 2003
|
||
|
||
|
||
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
|
||
|
||
|
||
|
||
Legg Expires 7 November 2003 [Page 4]
|
||
|
||
INTERNET-DRAFT Generic String Encoding Rules May 7, 2003
|
||
|
||
|
||
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.
|
||
|
||
|
||
|
||
Legg Expires 7 November 2003 [Page 5]
|
||
|
||
INTERNET-DRAFT Generic String Encoding Rules May 7, 2003
|
||
|
||
|
||
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.
|
||
|
||
|
||
|
||
|
||
Legg Expires 7 November 2003 [Page 6]
|
||
|
||
INTERNET-DRAFT Generic String Encoding Rules May 7, 2003
|
||
|
||
|
||
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
|
||
|
||
|
||
|
||
Legg Expires 7 November 2003 [Page 7]
|
||
|
||
INTERNET-DRAFT Generic String Encoding Rules May 7, 2003
|
||
|
||
|
||
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>
|
||
|
||
|
||
|
||
Legg Expires 7 November 2003 [Page 8]
|
||
|
||
INTERNET-DRAFT Generic String Encoding Rules May 7, 2003
|
||
|
||
|
||
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
|
||
|
||
|
||
|
||
Legg Expires 7 November 2003 [Page 9]
|
||
|
||
INTERNET-DRAFT Generic String Encoding Rules May 7, 2003
|
||
|
||
|
||
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
|
||
|
||
|
||
|
||
Legg Expires 7 November 2003 [Page 10]
|
||
|
||
INTERNET-DRAFT Generic String Encoding Rules May 7, 2003
|
||
|
||
|
||
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
|
||
|
||
|
||
|
||
|
||
|
||
Legg Expires 7 November 2003 [Page 11]
|
||
|
||
INTERNET-DRAFT Generic String Encoding Rules May 7, 2003
|
||
|
||
|
||
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
|
||
|
||
|
||
|
||
Legg Expires 7 November 2003 [Page 12]
|
||
|
||
INTERNET-DRAFT Generic String Encoding Rules May 7, 2003
|
||
|
||
|
||
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
|
||
|
||
|
||
|
||
Legg Expires 7 November 2003 [Page 13]
|
||
|
||
INTERNET-DRAFT Generic String Encoding Rules May 7, 2003
|
||
|
||
|
||
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
|
||
|
||
|
||
|
||
Legg Expires 7 November 2003 [Page 14]
|
||
|
||
INTERNET-DRAFT Generic String Encoding Rules May 7, 2003
|
||
|
||
|
||
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
|
||
|
||
|
||
|
||
Legg Expires 7 November 2003 [Page 15]
|
||
|
||
INTERNET-DRAFT Generic String Encoding Rules May 7, 2003
|
||
|
||
|
||
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
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
Legg Expires 7 November 2003 [Page 16]
|
||
|