Re: What padding do we use?

Hi,

From:  Christian Geuer-Pollmann <geuer-pollmann@nue.et-inf.uni-siegen.de>
Date:  Mon, 29 Oct 2001 13:44:21 +0100
To:  reagle@w3.org
Cc:  XML Encryption WG <xml-encryption@w3.org>
Message-ID:  <3635681325.1004363061@pinkpanther>

>Hi Joseph,
>
>in [1], I did not find any information about what padding mechanism we use? 
>PKCS7/PKCS5?

This depends on which algorithm you are talking about.

For TripleDES, and AES, I suppose we should continue to go with
whatever S/MIME does / will do.

For key transport, the padding is explicitly given for RSA 1.5. It's
complicated for RSA-OAEP but is given in the referenced RFC.

For Symmetric Key Wrap, the normal case of a TripleDES wrap of a
TripleDES key or any key that is a multile of 64 bit (i.e., all AES
keys) needs no padding and one would assume that NSA will define
appropriate padding for AES wrapping of AES keys. Since a TripleDES
key is the same size (192 bits) as an allowed AES key, it will
presumably be possible to AES wrap it like a 192 bit AES key. However,
I suppose, that we should either restrict TripleDES wrapping to keys
that are a multiple of 64 bits or say how to pad other lengths. For
AES, I'd prefer not to change any text until we see the NSA
recommendation.

>And for AES which allows block sizes of 128, 192 and 256 bit, we should 
>explicitly state that we use a block size of 128 bit (OK, the IV is 128 bit 
>and that should be a hint for the block size, but writing it down would be 
>clearer).

The (draft) NIST standard allows only block size 128 bits, but there
is no harm in mentioning this explicitly.

>Best regards,
>Christian

Thanks,
Donald

>[1] http://www.w3.org/Encryption/2001/Drafts/xmlenc-core/

Received on Tuesday, 30 October 2001 12:18:31 UTC