Hi David, On Mon, November 12, 2012 3:39 pm, David McGrew (mcgrew) wrote: > > > On 11/12/12 3:21 PM, "Dan Harkins" <[email protected]> wrote: > >> >> Hi Mike, >> >>> From: Mike Jones >>> <[email protected]<mailto:[email protected]>> >>> Date: Monday, November 12, 2012 1:55 PM >>> To: Cisco Employee <[email protected]<mailto:[email protected]>>, >>> "[email protected]<mailto:[email protected]>" >>> <[email protected]<mailto:[email protected]>>, >>> "[email protected]<mailto:[email protected]>" >>> <[email protected]<mailto:[email protected]>> >>> Subject: RE: [Cfrg] Authenticated Encryption with AES-CBC and HMAC-SHA, >>> version 01 >>> >>> As background, if there was a version of this spec that did not assume >>> that the parameters would be concatenated together in a specific way, >>>but >>> left them as independent inputs and outputs, as AES GCM and AES CTR do, >>>it >>> would be a better match for JOSE¹s use case. >> >> I encourage you to look into SIV mode, an AEAD scheme found in >>RFC 5297. SIV was defined by Rogaway and Shrimpton (in a paper >>found in the RFC) and is provably secure. >> >> It takes a vector of input as additional authenticated data which will >>be authenticated, and a plaintext which will be authenticated and >>encrypted. It does not assume that the parameters are concatenated >>together, it's just a vector of separate inputs. >> >> Additionally, SIV mode does not require a random IV/nonce. It works >>just fine if you have one, and it won't collapse if it is repeated (as >> GCM >>does) or is predictable (as CBC-HMAC does), and it works if you don't >>have, or want to have, one. In that fashion it is more robust than other >>AEAD schemes. The downside is that it's slower than GCM but is probably >>faster than CBC-HMAC with SHA2. > > AES-SIV is in several ways technically superior to AES-CBC-HMAC-SHA. > However, the motivation to use the latter algorithm is its widespread > availability, as I understand it. Mike and some other folks did a survey > of what crypto that is available. (Perhaps someone can send a reference, > it is a good survey.)
Well, there is no widespread availability of AES-CBC-HMAC-SHA either. There may be availability of AES-CBC and HMAC-SHA separately but then there is, probably, availability of AES-CTR and AES-CMAC too and that is all SIV is, a provably secure construction of those two primitives. > Despite SIV's flexibility, it doesn't address Mike's complaint, because it > does not have an authentication tag that is separate from the ciphertext. > Instead, it has the synthetic IV (which acts like an auth tag) combined > with the ciphertext. Ahh, I missed that. But I think that is probably a trivial complaint of any 5116 AEAD scheme. It should be straightforward to extract the specific sub-string from the bitstring returned by any of the appropriate schemes if he wants to copy the IV/MAC/tag/whatever into a field that is separate from the encrypted plaintext. > As an aside, if SIV is used for JOSE, it can use the RFC 5116 interface > (see Sections 6.1-6.3 of the SIV RFC) and essentially would need to do so. Good point! Regards, Dan. > David > >> >> regards, >> >> Dan. >> >> >> > > _______________________________________________ jose mailing list [email protected] https://www.ietf.org/mailman/listinfo/jose
