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From: David Howells <dhowells@redhat.com>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: dhowells@redhat.com, Bruce Fields <bfields@fieldses.org>,
	Chuck Lever <chuck.lever@oracle.com>,
	CIFS <linux-cifs@vger.kernel.org>,
	Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
	Herbert Xu <herbert@gondor.apana.org.au>,
	"open list:BPF JIT for MIPS (32-BIT AND 64-BIT)" 
	<netdev@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Trond Myklebust <trond.myklebust@hammerspace.com>,
	Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
	linux-fsdevel@vger.kernel.org, linux-afs@lists.infradead.org
Subject: Re: Why the auxiliary cipher in gss_krb5_crypto.c?
Date: Mon, 07 Dec 2020 14:15:00 +0000	[thread overview]
Message-ID: <482243.1607350500@warthog.procyon.org.uk> (raw)
In-Reply-To: <CAMj1kXH_gEjgZKx=8uQgv=ckBqTVoh3vrHj=O-nY-nm5VMgLaA@mail.gmail.com>

Ard Biesheuvel <ardb@kernel.org> 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


  parent reply	other threads:[~2020-12-07 14:16 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-12 12:57 [RFC][PATCH 00/18] crypto: Add generic Kerberos library David Howells
2020-11-12 12:57 ` [PATCH 01/18] crypto/krb5: Implement Kerberos crypto core David Howells
2020-11-12 12:58 ` [PATCH 02/18] crypto/krb5: Add some constants out of sunrpc headers David Howells
2020-11-12 12:58 ` [PATCH 03/18] crypto/krb5: Provide infrastructure and key derivation David Howells
2020-11-12 12:58 ` [PATCH 04/18] crypto/krb5: Implement the Kerberos5 rfc3961 " David Howells
2020-11-12 12:58 ` [PATCH 05/18] crypto/krb5: Implement the Kerberos5 rfc3961 encrypt and decrypt functions David Howells
2020-11-12 12:58 ` [PATCH 06/18] crypto/krb5: Implement the Kerberos5 rfc3961 get_mic and verify_mic David Howells
2020-11-12 12:58 ` [PATCH 07/18] crypto/krb5: Implement the AES enctypes from rfc3962 David Howells
2020-11-12 12:58 ` [PATCH 08/18] crypto/krb5: Implement crypto self-testing David Howells
2020-11-12 12:58 ` [PATCH 09/18] crypto/krb5: Implement the AES enctypes from rfc8009 David Howells
2020-11-12 12:59 ` [PATCH 10/18] crypto/krb5: Implement the AES encrypt/decrypt " David Howells
2020-11-12 12:59 ` [PATCH 11/18] crypto/krb5: Add the AES self-testing data " David Howells
2020-11-12 12:59 ` [PATCH 12/18] crypto/krb5: Implement the Camellia enctypes from rfc6803 David Howells
2020-11-12 12:59 ` [PATCH 13/18] rxrpc: Add the security index for yfs-rxgk David Howells
2020-11-12 12:59 ` [PATCH 14/18] rxrpc: Add YFS RxGK (GSSAPI) security class David Howells
2020-11-12 12:59 ` [PATCH 15/18] rxrpc: rxgk: Provide infrastructure and key derivation David Howells
2020-11-12 12:59 ` [PATCH 16/18] rxrpc: rxgk: Implement the yfs-rxgk security class (GSSAPI) David Howells
2020-11-12 13:00 ` [PATCH 17/18] rxrpc: rxgk: Implement connection rekeying David Howells
2020-11-12 13:00 ` [PATCH 18/18] rxgk: Support OpenAFS's rxgk implementation David Howells
2020-11-12 13:44 ` [RFC][PATCH 00/18] crypto: Add generic Kerberos library David Howells
2020-11-12 14:36 ` Chuck Lever
2020-11-12 15:42 ` David Howells
2020-11-12 15:49   ` Chuck Lever
2020-11-12 16:54   ` David Howells
2020-11-12 21:07     ` Bruce Fields
2020-11-12 21:09       ` Chuck Lever
2020-11-12 18:37 ` J. Bruce Fields
2020-11-12 18:39   ` Chuck Lever
2020-11-26  6:33 ` Herbert Xu
2020-11-26  8:19 ` David Howells
2020-11-27  5:07   ` Herbert Xu
2020-12-01  8:44   ` David Howells
2020-12-01  8:46     ` Herbert Xu
2020-12-01  9:12     ` David Howells
2020-12-01 10:36       ` Herbert Xu
2020-12-04 14:59 ` Why the auxiliary cipher in gss_krb5_crypto.c? David Howells
2020-12-04 15:46   ` Bruce Fields
2020-12-04 16:05     ` Chuck Lever
2020-12-04 16:14     ` Bruce Fields
2020-12-04 16:01   ` David Howells
2020-12-04 16:03     ` Bruce Fields
2020-12-04 16:50     ` David Howells
2020-12-04 17:06       ` Ard Biesheuvel
2020-12-04 17:19       ` David Howells
2020-12-04 17:35         ` Ard Biesheuvel
2020-12-04 21:08           ` Herbert Xu
2020-12-07  8:24           ` David Howells
2020-12-07 12:01         ` David Howells
2020-12-07 13:08           ` Ard Biesheuvel
2020-12-07 14:15           ` David Howells [this message]
2020-12-08  8:27             ` Ard Biesheuvel
2020-12-08  9:18             ` David Howells
2020-12-04 18:13   ` Theodore Y. Ts'o
2020-12-08 13:25 ` David Howells
2020-12-08 14:04   ` Ard Biesheuvel
2020-12-08 14:13   ` David Howells
2020-12-08 14:02 ` David Howells

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