Re: RE: Draft Minutes from 010611 Teleconf (changes)

Reversibility of Transform operations from CipherReference has
absolutely nothing to do with getting back the original bits that were
entryped.  These are transforms that are done to get the CIPHER
TEXT. Obviously, they can not have anything whatsoever to do with what
you get for plain text after decrypting.

There can be Transform like operations performed before encryption and
after decryption. In fact, we recomment using C14N with comments
before encryption if it is desired to preserve the context. But such
Transform operations do not appear in CipherReference.

Donald

PS: If data being encrypted is binary or being treated as binary,
getting "the same bits back" makes sense. However, as you say, if data
is XML, getting the same bits back is meaningless.  All applications
that conform to the XML 1.0 standard are required NOT to treat
anything they process as XML as a mere string of character codes or
logical characters. They are REQUIRED to treat it as a logically
structured entity in which certain "bits" in the octet string
representation (such as exact external coding of line terminations,
white space inside start and end tags, ordering of attributes) are
REQUIRED to be thrown away.

From:  edsimon@xmlsec.com
Message-ID:  <3B23C10500001268@mail.san.yahoo.com>
Date:  Tue, 12 Jun 2001 10:21:47 -0400
In-Reply-To:   <4.3.2.7.2.20010612085117.00b71508@localhost>
To:  xml-encryption@w3.org

>Ed wrote
>>>We're dropping the discussion of 'reversible transforms' from the spec
>so
>>>the last item is moot anyway.
>then Joseph wrote
>>BTW: I still thought a sentence or two was merited, so have a look at the
>>
>>most recent proposed edits I posted yesterday.
>>http://www.w3.org/Encryption/2001/05/11-proposal.html#sec-CipherReference
>
>Transforms must be completely reversible iff an application requires that
>the decrypted result be bit-by-bit or character-by-character exactly what
>was encrypted.  In pre-XML encryption, it would generally be considered
>a problem if the post-decryption bits didn't exactly match the pre-encryption
>bits.  However, in the brave new world of XML, some applications may not
>care if when
><element   attr1='blah1'  attr2="blah2"    />
>gets encrypted but the decrypted result is
><element attr2="blah2" attr1="blah1"  />
>or something else.
>
>On the other hand, some applications will want character-by-character and
>even bit-by-bit parity between the encrypted version and the decrypted version.
> These applications will have greater constraints on the types of transforms
>they can use because of the higher degree of reversibility required.
>
>I think XML Encryption is flexible enough to support the full ambit of reversibility
>requirements.  I'm not arguing (at this point) for any requirements on the
>reversibility of transforms; I'm just using this posting as a way of thinking
>out loud and soliciting feedback from others.  Jim and Don have already
>had some good points and I just want to make sure there is a good common
>understanding of this topic.
>
>Regards, Ed
>
>
>

Received on Tuesday, 12 June 2001 10:48:34 UTC