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Re: EncryptionMethod in XMLEnc and SignatureMethod in XMLDSig

From: Aleksey Sanin <aleksey@aleksey.com>
Date: Mon, 01 Apr 2002 14:13:44 -0800
Message-ID: <3CA8DB98.8090603@aleksey.com>
To: Christian Geuer-Pollmann <geuer-pollmann@nue.et-inf.uni-siegen.de>
CC: xml-encryption@w3.org
First of all, I do not suggest to make EncryptionMethod required
I think that *both* should be optional. Next as far as I can remember,
the basic cryptography rule says that the only secret is the key.
Everything  else is known to everyone. IMHO, any security system
based on the "secret algorithm" is a snake oil.
I belive that the only reason to ommit EncryptionMethod is to save
some space when application knows this from the context. And I think
the same reasons apply to the signature.
At the end of all, it looks natural to have both elements treated in the 
way, doesn't it?


Christian Geuer-Pollmann wrote:

> --On Montag, 1. April 2002 12:01 -0800 Aleksey Sanin 
> <aleksey@aleksey.com> wrote:
>> Sorry for mistype, actually Imeant SignatureMethod in XMLDSig:
>> A minor issue but probably it's worth to fix it: the EncryptionMethod
>> in XMLEncryption and SignatureMethod in XMLDSig both have the same
>> meaning: algorithm selection. However, EncryptionMethod is *optional*
>> element and SignatureMethod is *required*. From my point of view it is
>> inconsistent. Either both should be required or both should be optional.
>> I would prefer the second (both optional) since application can have 
>> this
>> information from the context.
> Hi Aleksey,
> from Schema point, you're right. But I think they have different 
> security properties:
> For digital signatures (non-repudiation), the signed want's to state 
> that he made a statement and he want that the binding between his 
> identity (Certificate) and the signed contents is non-ambiguous. So it 
> wouldn't make sense to omit the ds:SignatureMethod because that would 
> let space for discussions (which algorithm was used).
> For encryption (confidentiality), there are people who like "security 
> by obscurity" as an additional point in their encryption system. So 
> making the xenc:EncryptionMethod REQUIRED would force people to expose 
> information which they probably do not want to disclose.
> Maybe this is one motivation for this decision. But from implementors 
> point of view, it adds some complexity.
> Regards,
> Christian
Received on Monday, 1 April 2002 17:14:37 UTC

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