For multiple recipients using GCM with a single CEK and IV we can logically have 0 AAD segments or 1 AAD segment.
That is just the reality of the situation. One possible solution is to the GCM issue is to have 1 AAD segment containing the envelope information for all recipients. I understand for people wanting 0 AAD segments that will not be there first choice. The downside of this is that you can't incrementally add recipients, they all need to be known upfront to include the info in the AAD. What I don't know is if there is really any compelling use-case for incremental addition of recipients without re-encrypting (changing the IV atleast) John B. . On 2013-04-25, at 4:14 PM, Mike Jones <[email protected]> wrote: > Hi Richard, > > Actually, there are four goals in play: > > 1. GCM > 2. Efficient encoding for multiple recipients > 3. Header integrity protection > 4. Independent protection of each recipient’s headers > > Per my response to Russ, by giving up 4, we can achieve 1, 2, and 3. (Credit > goes to John Bradley for this solution.) > > -- Mike > > From: Richard Barnes [mailto:[email protected]] > Sent: Thursday, April 25, 2013 11:14 AM > To: Mike Jones > Cc: Jim Schaad; [email protected] > Subject: Re: [jose] I-D Action: draft-ietf-jose-json-web-encryption-09.txt > > Mike, > > Your facts are right, but your conclusions are wrong. > > We have three mutually incompatible goals here: > 1. GCM > 2. Efficient encoding for multiple recipients > 3. Header integrity > > We can have any two of these, but not all three. If we try to do all three > (JWE-08), then we end up with the vulnerability identified in the CFRG > thread. So we need to choose which one to get rid of. > > Getting rid of GCM is clearly not the right answer, as evidenced by the > reaction in this thread. There are clear, concrete use reasons to support > multiple recipients, but not for header integrity. And header integrity can > be "polyfilled" with an optional feature, for those who are willing to break > the multiple recipient case. Clearly, header integrity is the weakest link > here. > > JWE-09 is the reductio ad absurdum of header integrity. Let's do the logical > thing and stop the absurdity. > > --Richard > > > > > On Thu, Apr 25, 2013 at 2:48 AM, Mike Jones <[email protected]> > wrote: > Jim - I am surprised that you would say that my co-authors Eric Rescorla or > Joe Hildebrand or the working group would advocate using AES GCM in a way > that would result in severe security vulnerabilities - in particular, > allowing attackers to obtain the XOR of the messages to multiple recipients > encrypted using GCM - a vulnerability identified by the CFRG. > > Not stating this in the document would seem to me to be highly irresponsible, > given the brittleness of GCM in this regard, as identified by the CRFG. As I > said to Richard Barnes over dinner last night, while unpleasant, and possibly > surprising to those who aren't familiar to how GCM actually works, as an > editor, I viewed including the statement that "AES GCM MUST NOT be used when > using the JWE JSON Serialization for multiple recipients, since this would > result in the same Initialization Vector and Plaintext values being used for > multiple GCM encryptions" as necessary, and "truth in advertising". > > -- Mike > > -----Original Message----- > From: [email protected] [mailto:[email protected]] On Behalf Of Jim > Schaad > Sent: Wednesday, April 24, 2013 9:07 PM > To: Mike Jones > Cc: [email protected] > Subject: Re: [jose] I-D Action: draft-ietf-jose-json-web-encryption-09.txt > > Mike, > > AES GCM MUST NOT be used when using the JWE JSON Serialization for > multiple recipients, since this would result in the same > Initialization Vector and Plaintext values being used for multiple > GCM encryptions. > > I doubt your co-authors would agree with this. > I doubt the working group with agree with this. > I know that at least one co-chair does not agree with this I can predict that > the AD and IESG along with the security directorate would crucify me if I > allowed this to stand in the document.. > > Jim > > > > > -----Original Message----- > > From: [email protected] [mailto:[email protected]] On Behalf > > Of [email protected] > > Sent: Tuesday, April 23, 2013 5:29 PM > > To: [email protected] > > Cc: [email protected] > > Subject: [jose] I-D Action: draft-ietf-jose-json-web-encryption-09.txt > > > > > > A New Internet-Draft is available from the on-line Internet-Drafts > directories. > > This draft is a work item of the Javascript Object Signing and > > Encryption Working Group of the IETF. > > > > Title : JSON Web Encryption (JWE) > > Author(s) : Michael B. Jones > > Eric Rescorla > > Joe Hildebrand > > Filename : draft-ietf-jose-json-web-encryption-09.txt > > Pages : 54 > > Date : 2013-04-23 > > > > Abstract: > > JSON Web Encryption (JWE) is a means of representing encrypted > > content using JavaScript Object Notation (JSON) data structures. > > Cryptographic algorithms and identifiers for use with this > > specification are described in the separate JSON Web Algorithms (JWA) > > specification. Related digital signature and MAC capabilities are > > described in the separate JSON Web Signature (JWS) specification. > > > > > > The IETF datatracker status page for this draft is: > > https://datatracker.ietf.org/doc/draft-ietf-jose-json-web-encryption > > > > There's also a htmlized version available at: > > http://tools.ietf.org/html/draft-ietf-jose-json-web-encryption-09 > > > > A diff from the previous version is available at: > > http://www.ietf.org/rfcdiff?url2=draft-ietf-jose-json-web-encryption-0 > > 9 > > > > > > Internet-Drafts are also available by anonymous FTP at: > > ftp://ftp.ietf.org/internet-drafts/ > > > > _______________________________________________ > > jose mailing list > > [email protected] > > https://www.ietf.org/mailman/listinfo/jose > > _______________________________________________ > jose mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/jose > _______________________________________________ > jose mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/jose > > _______________________________________________ > jose mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/jose
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