[Cryptography-dev] Low level API for Symmetric Encryption

[Donald Stufft]

On Aug 7, 2013, at 7:18 PM, Alex Gaynor <alex.gaynor at gmail.com> wrote:

> Another option is to compose them in the constructor: AES(keysize=256, mode=GCM) or so.
> 
> Alex

We'd still essentially be passing AES-256-GCM into OpenSSL afaik. So afaik it'd only look like composing. We're not handling (most) of the differences between the modes (and none of the differences for key size).

The mode classes could be stuff that handles the slight differences in how you call the API (for instance GCM has an additional call to EVP_EncryptUpdate to give it the AAD and a different calls to handle getting the MAC data. I'm not sure how well that'd translate? It might work ok.

> 
> 
> On Wed, Aug 7, 2013 at 4:12 PM, Donald Stufft <donald at stufft.io> wrote:
> 
> On Aug 7, 2013, at 6:32 PM, Jean-Paul Calderone <jean-paul at hybridcluster.com> wrote:
> 
> > On 08/07/2013 06:16 PM, Donald Stufft wrote:
> >> So to kick things off I'd like to get AES-GCM exposed and figured it could be a good way to start the ball rolling for figuring out how we want to expose symmetric ciphers at the low level API.
> >>
> >> I'm thinking cryptography.primitives.aes which has classes named like AES128GCM, AES256CBC, etc. The obvious naming scheme being AlgorithmKeysizeMode.
> >>
> >>
> >
> > GCM (CBC, etc) is a mode of operation that is applicable to arbitrary
> > block ciphers.
> >
> > Why should it be tied to "AES128"?  Why wouldn't you GCM(AES128())?  If
> > you're talking about primitives, AES128 is more primitive than GCM on
> > AES128.  And GCM isn't specific to AES, so I don't see
> > cryptography.primitives.aes as the proper home for it.
> >
> > I hope these aren't questions with highly obvious answers.
> 
> As far as I know (and I could be wrong? I don't know OpenSSL guts that well) OpenSSL doesn't do composition like that, in order to get AES-128-GCM you pass that in.
> 
> Is there a way to access openssl where you're composing GCM with AES128? If not I think we'd be stuck do some sort of "combine variables of the classes AES128 and GCM to make the name AES-128-GCM to pass into openssl" thing which doesn't feel particularly clean to me?
> 
> 
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> Donald Stufft
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-----------------
Donald Stufft
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