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Security Consideration section for MTOM

From: Martin Gudgin <mgudgin@microsoft.com>
Date: Mon, 9 Feb 2004 23:32:46 -0800
Message-ID: <DD35CC66F54D8248B6E04232892B63380121F77E@RED-MSG-43.redmond.corp.microsoft.com>
To: <xml-dist-app@w3.org>

I took an action on the 2004-02-03 call to write up a security
considerations section for MTOM. Here's a first cut. Comments welcome.

Cheers

Gudge


Message Integrity

The integrity of SOAP messages transmitted using the MTOM HTTP Binding
may need to be ensured. As such messages can be transformed to an XML
Information Set, from which an XPath 1.0 Data Model can be inferred,
existing XML Digital Signature techniques can be used to protect such
messages. Digests computed for this purpose would be over the base64
characters rather than the xbinc:Include elements. Existing
canonicalization algorithms[C14N,EXCC14N] do not permit computing
digests over the binary octets directly. Future canonicalization
algorithms could describe a more efficient algorithm.

Care should be taken when constructing an XPath node set as input to a
canonicalization algorithm. Specifically, node sets where adjacent nodes
are text nodes containing base64 characters should be avoided as an
attacker could move base64 characters from one node to another without
changing the digest value.


Message Confidentiality

The confidentiality of SOAP messages transmitted using the MTOM HTTP
Binding may need to be ensured. As such messages can be transformed to
an XML Information Set existing XML Encryption techniques can be used to
protect such messages. Any part of a message can be encrypted, whether
it includes base64 characters or not. The resulting CipherData can then
be optimized because the content of such an element is base64
characters.

In future a transform algorithm for use with xenc:CipherReference could
provide a more efficient processing model where the raw octets are
encrypted directly.
Received on Tuesday, 10 February 2004 02:32:53 UTC

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