Clause 20.5 of X.680 [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"
3.20. 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
the <distinguishedName> rule in Section 3 of RFC 2253 [5], and then
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 RFC
2253 [5], and then 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 RFC 2156 [2], and then encoded as if it were an
IA5String value.
ORAddressValue = StringValue
4. GSER Transfer Syntax
The following OBJECT IDENTIFIER has been assigned by Adacel
Technologies, under an arc assigned to Adacel by Standards Australia,
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.
5. 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 the original GSER octet encoding. Therefore, GSER MUST 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 a Distinguished Encoding Rules (DER) [12]
encoding to GSER and back to DER may not reproduce the original DER
encoding. Therefore, GSER MUST NOT be used to re-encode, whether for
storage or transmission, ASN.1 abstract values whose original binary
encoding must be recoverable. Such recovery is needed for the
verification of digital signatures. In such cases, protocols ought
to use DER or a DER-reversible encoding.
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.
6. References
6.1. 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 (07/02) | ISO/IEC 8824-1:2002
Information technology - Abstract Syntax Notation One (ASN.1):
Specification of basic notation
[9] ITU-T Recommendation X.681 (07/02) | ISO/IEC 8824-2:2002
Information technology - Abstract Syntax Notation One (ASN.1):
Information object specification
[10] ITU-T Recommendation X.682 (07/02) | ISO/IEC 8824-3:2002
Information technology - Abstract Syntax Notation One (ASN.1):
Constraint specification
[11] ITU-T Recommendation X.683 (07/02) | ISO/IEC 8824-4:2002
Information technology - Abstract Syntax Notation One (ASN.1):
Parameterization of ASN.1 specifications
[12] ITU-T Recommendation X.690 (07/02) | ISO/IEC 8825-1:2002
Information technology - ASN.1 encoding rules: Specification of
Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and
Distinguished Encoding Rules (DER)
6.2. Informative References
[13] Hovey, R. and S. Bradner, "The Organizations Involved in the
IETF Standards Process", BCP 11, RFC 2028, October 1996.
[14] Hodges, J. and R. Morgan, "Lightweight Directory Access Protocol
(v3): Technical Specification", RFC 3377, September 2002.
[15] Legg, S., "Common Elements of Generic String Encoding Rules
(GSER) Encodings", RFC 3642, October 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
7. Intellectual Property Notice
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pertain to the implementation or use of the technology described in
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The IETF invites any interested party to bring to its attention any
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Director.
8. 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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