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RE: What's in a EncryptedKeys' CipherData?

From: Blair Dillaway <blaird@microsoft.com>
Date: Fri, 6 Apr 2001 15:10:34 -0700
Message-ID: <AA19CFCE90F52E4B942B27D42349637921F96B@red-msg-01.redmond.corp.microsoft.com>
To: "Joseph M. Reagle Jr." <reagle@w3.org>
Cc: <jimsch@exmsft.com>, "XML Encryption WG " <xml-encryption@w3.org>
My apologies, I misunderstood you point.

The EncryptedKey element contains all the information 
you need to properly decrypt the CipherData and 
obtain the octet sequence for the raw key material.  
But you are correct in that you don't know what to 
do with this until you go to decrypt an EncryptedData 
and discover what its EncryptionMethod is.

In general, I don't see that this creates any problems.  
All keys look like octet sequences of random bits until
you plug them into a specific algorithm for use.

The one case where someone might care is if they want
to cache keys inside some hardware device that supports
multiple algorithms.  If they recieved an EncryptedKey
to cache for later use with EncryptedData, then they
couldn't load the key into the device until the 
first EncryptedData arrives.  

Do folks think this is an issue we need to address?

Blair
 



-----Original Message-----
From: Joseph M. Reagle Jr. [mailto:reagle@w3.org]
Sent: Friday, April 06, 2001 2:48 PM
To: Blair Dillaway
Cc: jimsch@exmsft.com; XML Encryption WG 
Subject: RE: What's in a EncryptedKeys' CipherData?


At 14:23 4/6/2001 -0700, Blair Dillaway wrote:
>Well no.  Either you know the EncryptionMethod for the EncryptedKey
>implicitly
>or else it is provided by the EncryptionMethod element within the
>EncryptedKey element. EncryptionMethod information for an EncryptedData
>isn't relevant.

Yes it is. (I think). If I want to know of what type of data that raw
octet 
set (when decrypted from within an EncryptedKey is), I have to go
elsewhere.

I now realize were my confusion from this and NameKey is coming from.

If I have an EncryptedData that is relying upon and EncryptedKey,
consider 
the symmetric key secured in that EncryptedKey. That set of octets has
some 
properties.

(octets)
    --name--> NameKey element of the parent EncryptedKey
    --type--> EncryptionMethod of a referring EncryptedData

The tricky bit is when you look at the proposed structures, some of the 
elements/attributes (like KeyInfo) are used to convey information about
that 
data object (EncryptedData and EncryptedKey) and others are used to
convey 
information about a resource to which to they relate (but doesn't become

revealed until they are processed.)


__
Joseph Reagle Jr.                 http://www.w3.org/People/Reagle/
W3C Policy Analyst                mailto:reagle@w3.org
IETF/W3C XML-Signature Co-Chair   http://www.w3.org/Signature
W3C XML Encryption Chair          http://www.w3.org/Encryption/2001/
Received on Friday, 6 April 2001 21:07:33 GMT

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