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Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: References: <20201204154626.GA26255@fieldses.org> <2F96670A-58DC-43A6-A20E-696803F0BFBA@oracle.com> <160518586534.2277919.14475638653680231924.stgit@warthog.procyon.org.uk> <118876.1607093975@warthog.procyon.org.uk> <122997.1607097713@warthog.procyon.org.uk> <20201204160347.GA26933@fieldses.org> <125709.1607100601@warthog.procyon.org.uk> <127458.1607102368@warthog.procyon.org.uk> <468625.1607342512@warthog.procyon.org.uk> To: Ard Biesheuvel Cc: dhowells@redhat.com, Bruce Fields , Chuck Lever , CIFS , Linux NFS Mailing List , Herbert Xu , "open list:BPF JIT for MIPS (32-BIT AND 64-BIT)" , Linux Kernel Mailing List , Trond Myklebust , Linux Crypto Mailing List , linux-fsdevel@vger.kernel.org, linux-afs@lists.infradead.org Subject: Re: Why the auxiliary cipher in gss_krb5_crypto.c? MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <482242.1607350500.1@warthog.procyon.org.uk> Date: Mon, 07 Dec 2020 14:15:00 +0000 Message-ID: <482243.1607350500@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Precedence: bulk List-ID: X-Mailing-List: linux-crypto@vger.kernel.org Ard Biesheuvel wrote: > > I wonder if it would help if the input buffer and output buffer didn't > > have to correspond exactly in usage - ie. the output buffer could be used > > at a slower rate than the input to allow for buffering inside the crypto > > algorithm. > > > > I don't follow - how could one be used at a slower rate? I mean that the crypto algorithm might need to buffer the last part of the input until it has a block's worth before it can write to the output. > > The hashes corresponding to the kerberos enctypes I'm supporting are: > > > > HMAC-SHA1 for aes128-cts-hmac-sha1-96 and aes256-cts-hmac-sha1-96. > > > > HMAC-SHA256 for aes128-cts-hmac-sha256-128 > > > > HMAC-SHA384 for aes256-cts-hmac-sha384-192 > > > > CMAC-CAMELLIA for camellia128-cts-cmac and camellia256-cts-cmac > > > > I'm not sure you can support all of those with the instructions available. > > It depends on whether the caller can make use of the authenc() > pattern, which is a type of AEAD we support. Interesting. I didn't realise AEAD was an API. > There are numerous implementations of authenc(hmac(shaXXX),cbc(aes)), > including h/w accelerated ones, but none that implement ciphertext > stealing. So that means that, even if you manage to use the AEAD layer to > perform both at the same time, the generic authenc() template will perform > the cts(cbc(aes)) and hmac(shaXXX) by calling into skciphers and ahashes, > respectively, which won't give you any benefit until accelerated > implementations turn up that perform the whole operation in one pass over > the input. And even then, I don't think the performance benefit will be > worth it. Also, the rfc8009 variants that use AES with SHA256/384 hash the ciphertext, not the plaintext. For the moment, it's probably not worth worrying about, then. If I can manage to abstract the sunrpc bits out into a krb5 library, we can improve the library later. David