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Re: Base64 -- do we really want/need line breaks every 76 characters?

From: Martin Duerst <duerst@w3.org>
Date: Thu, 24 May 2001 08:01:58 +0900
Message-Id: <>
To: "Brian LaMacchia" <bal@microsoft.com>, <w3c-ietf-xmldsig@w3.org>
Cc: www-xml-schema-comments@w3.org
After seeing all the discussion, I'm okay with long lines as such.
But there is still the problem that XML Schema doesn't allow that,
because it references RFC 2045 directly, without anything else.
This is a problem on both sides:

- XML Signature cannot use the XML Schema datatype as it stands
   (and extension or restriction won't work here)
- XML Schema should consider changing their definition of
   Base64 to include longer lines, because it seems that that's
   widely used in practice. Whether that can be done as a corrigendum
   to Schema 1.0 or whether that has to go into Schema 1.1, I don't

I have copied www-xml-schema-comments. Schema experts, please see
the other messages in this thread

Regards,   Martin.

At 17:31 01/05/22 -0700, Brian LaMacchia wrote:
>Currently, XMLDSIG references RFC 2045 (one of the MIME RFCs) for a
>definition of Base64 encoding/decoding.  (See section 6.8 of [1].)  It
>has been pointed out to me that RFC 2045 *requires* that Base64-encoded
>content have line breaks at least every 76 characters.  Paragraph 6
>reads as follows:
>    The encoded output stream must be represented in lines of no more
>    than 76 characters each.  All line breaks or other characters not
>    found in Table 1 must be ignored by decoding software.  In base64
>    data, characters other than those in Table 1, line breaks, and other
>    white space probably indicate a transmission error, about which a
>    warning message or even a message rejection might be appropriate
>    under some circumstances.
>I can't see any reason for XMLDSIG to inherit a line-length limitation
>that appears to have been there for mail-specific reasons.  The SOAP 1.1
>submission [2] removes the line length limitation in their use of
>Base64; Section 5.4.3 of SOAP reads as follows:
>    The recommended representation of an opaque array of bytes is the
>    'base64' encoding defined in XML Schemas [10][11], which uses the
>    base64 encoding algorithm defined in 2045 [13]. However, the line
>    length restrictions that normally apply to base64 data in MIME do
>    not apply in SOAP. A "SOAP-ENC:base64" subtype is supplied for use
>    with SOAP.
>I propose that XMLDSIG adopt language similar to SOAP and not require
>applications to insert line breaks at least every 76 characters.
>(Conforming implementation will still accept line-limited encodings
>since they have to ignore any found whitespace in the Base64 string.)
>                                         --bal
>[1] http://www.ietf.org/rfc/rfc2045.txt
>[2] http://www.w3.org/TR/SOAP/
Received on Wednesday, 23 May 2001 21:14:48 UTC

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