Subject: [jose] Theroetical use of SIV AEAD mode in JOSE

From: "Jim Schaad" <[email-masked]>
Date: Thu, 25 Apr 2013 14:03:49 -0700

First, I am not advocating that we should add SIV mode as a standard
encryption algorithm to the JOSE specifications.  However SIV mode has some
interesting properties and has been publicly declared as being IP free so I
want to make sure that we do not preclude the use of SIV mode if somebody
else wants to play with it.

A quick primer on how SIV mode works:

1.        Compute the IV to be used for the message.  IV = F(Authenticated
Data, Plain Text, Encryption Key)

2.       Encrypt the Plain Text     CipherText = AES-CTR(Plain Text, IV,
Encryption Key)  
Note that I have not looked it up and it has been a while, but I am pretty
sure that it does use CTR mode.

3.       Compute the authentication Tag    AT = IV

There are no problems with doing the encoding in that one can present the IV
as both the IV and the AT in the encoding so it is not as if one of these
fields becomes implicit.  However it does mean that the current encoding
format for multiple recipients is completely un-usable.  One could use the
format but it would need to be in a single recipient mode only.  This is
because the IV and the encrypted text would, of necessity, be unique for
each recipient.

Jim

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From: Russ Housley <[email-masked]>
Date: Thu, 25 Apr 2013 18:26:10 -0400

Jim:

I think that the advocates for SIV need to show how to apply it to multiple recipients and produce the same ciphertext.  Otherwise, it is equivalent to a separate message per recipient.  This is worse that the S/MIME solution for BCC recipients.

Russ

On Apr 25, 2013, at 5:03 PM, Jim Schaad wrote:

> First, I am not advocating that we should add SIV mode as a standard encryption algorithm to the JOSE specifications.  However SIV mode has some interesting properties and has been publicly declared as being IP free so I want to make sure that we do not preclude the use of SIV mode if somebody else wants to play with it.
>  
> 1.        Compute the IV to be used for the message.  IV = F(Authenticated Data, Plain Text, Encryption Key)
> 2.       Encrypt the Plain Text     CipherText = AES-CTR(Plain Text, IV, Encryption Key)  
> Note that I have not looked it up and it has been a while, but I am pretty sure that it does use CTR mode.
> There are no problems with doing the encoding in that one can present the IV as both the IV and the AT in the encoding so it is not as if one of these fields becomes implicit.  However it does mean that the current encoding format for multiple recipients is completely un-usable.  One could use the format but it would need to be in a single recipient mode only.  This is because the IV and the encrypted text would, of necessity, be unique for each recipient.
>  
> Jim
>

---

From: "Jim Schaad" <[email-masked]>
Date: Thu, 25 Apr 2013 15:52:03 -0700

Russ,

I don't understand this comment.  SIV can be used in CMS today without this
problem.  Since the encryption key would be common to all of the recipients
in CMS Authenticated Enveloped Data there are no problems with using it.
Thus it would be equivalent to the S/MIME BCC recipients solution.

This would only be an issue for CMS if all of the key management data were
included in the authentication process which it is not.

Jim

From: Russ Housley [mailto:[email-masked]] 
Sent: Thursday, April 25, 2013 3:26 PM
To: Jim Schaad
Cc: [email-masked]
Subject: Re: [jose] Theroetical use of SIV AEAD mode in JOSE

Jim:

I think that the advocates for SIV need to show how to apply it to multiple
recipients and produce the same ciphertext.  Otherwise, it is equivalent to
a separate message per recipient.  This is worse that the S/MIME solution
for BCC recipients.

Russ

 

Jim