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Encoding of Strings in DNames (X509IssuerSerial, X509SubjectName)

From: Gregor Karlinger <gregor.karlinger@iaik.at>
Date: Wed, 16 Jan 2002 14:21:09 +0100
To: "Joseph M. Reagle Jr." <reagle@w3.org>
Cc: "XMLSigWG" <w3c-ietf-xmldsig@w3.org>
Message-ID: <LBEPJAONIMDADHFHAEAOEEJLCMAA.gregor.karlinger@iaik.at>
Joseph,

currently applications conforming with XMLDSIG must encode DNames in
the way described in section 4.4.4 of the current draft [1]:

<specsnip>
  * Consider the string as consisting of Unicode characters.

  * Escape occurrences of the following special characters by
    prefixing it with the "\" character:

    - a "#" character occurring at the beginning of the string
    - one of the characters ",", "+", """, "\", "<", ">" or ";"

  * Escape all occurrences of ASCII control characters (Unicode range
    \x00 - \x 1f) by replacing them with "\" followed by a two digit
    hex number showing its Unicode number.

  * Escape any trailing white space by replacing "\ " with "\20".

  * Since a XML document logically consists of characters, not octets,
    the resulting Unicode string is finally encoded according to the
    character encoding used for producing the physical representation
    of the XML document.
</specsnip>

I think that there are two problems with these instructions:

(1) We claim that these instructions are conforming with RFC 2253 [2]. This
    is currently not true, since RFC 2253 demands the escaping of the
    whitespace character (ASCII code \x20) at the beginning and at the
    end of the string (see section 2.4).

(2) (a fundamental problem): The instructions in section 2.4 of [2] operate
    on a UTF8-String, i. e. in the octet domain. Our instructions operate
    on a Unicode string, i. e. in the character domain. Therefore I consider
    it useless to try to conform to RFC 2253 with the current instructions.

To solve the problems, I suggest:

- Do not state that the encoding of DNames conforms with RFC 2253, rather
  state that our instructions are similar to that of RFC 2253 (only similar
  because of the domain difference).

- Modify the instructions as follows:

  * Consider the string as consisting of Unicode characters.

  * Escape occurrences of the following special characters by
    prefixing it with the "\" character:

    - a "#" occurring at the beginning of the string
    - one of the characters ",", "+", """, "\", "<", ">" or ";"

  * Escape control characters that are not XML characters (\x00-\x08,
    \x0B-\x0C, \x0E-\x19).

  This is sufficient in order to produce text that consists of valid
  XML characters, and to be able to reparse the DName string.

Liebe Gruesse/Regards,
---------------------------------------------------------------
DI Gregor Karlinger
mailto:gregor.karlinger@iaik.at
http://www.iaik.at
Phone +43 316 873 5541
Institute for Applied Information Processing and Communications
Austria
---------------------------------------------------------------

---
[1]
http://www.w3.org/Signature/Drafts/xmldsig-core/Overview.html#sec-X509Data
[2] http://ietf.org/rfc/rfc2253.txt
Received on Wednesday, 16 January 2002 08:21:19 GMT

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