From: Bruce Fields <bfields@fieldses.org>
To: David Howells <dhowells@redhat.com>
Cc: 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>,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
Trond Myklebust <trond.myklebust@hammerspace.com>,
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: Fri, 4 Dec 2020 10:46:26 -0500 [thread overview]
Message-ID: <20201204154626.GA26255@fieldses.org> (raw)
In-Reply-To: <118876.1607093975@warthog.procyon.org.uk>
On Fri, Dec 04, 2020 at 02:59:35PM +0000, David Howells wrote:
> Hi Chuck, Bruce,
>
> Why is gss_krb5_crypto.c using an auxiliary cipher? For reference, the
> gss_krb5_aes_encrypt() code looks like the attached.
>
> >From what I can tell, in AES mode, the difference between the main cipher and
> the auxiliary cipher is that the latter is "cbc(aes)" whereas the former is
> "cts(cbc(aes))" - but they have the same key.
>
> Reading up on CTS, I'm guessing the reason it's like this is that CTS is the
> same as the non-CTS, except for the last two blocks, but the non-CTS one is
> more efficient.
CTS is cipher-text stealing, isn't it? I think it was Kevin Coffman
that did that, and I don't remember the history. I thought it was
required by some spec or peer implementation (maybe Windows?) but I
really don't remember. It may predate git. I'll dig around and see
what I can find.
--b.
>
> David
> ---
> nbytes = buf->len - offset - GSS_KRB5_TOK_HDR_LEN;
> nblocks = (nbytes + blocksize - 1) / blocksize;
> cbcbytes = 0;
> if (nblocks > 2)
> cbcbytes = (nblocks - 2) * blocksize;
>
> memset(desc.iv, 0, sizeof(desc.iv));
>
> if (cbcbytes) {
> SYNC_SKCIPHER_REQUEST_ON_STACK(req, aux_cipher);
>
> desc.pos = offset + GSS_KRB5_TOK_HDR_LEN;
> desc.fragno = 0;
> desc.fraglen = 0;
> desc.pages = pages;
> desc.outbuf = buf;
> desc.req = req;
>
> skcipher_request_set_sync_tfm(req, aux_cipher);
> skcipher_request_set_callback(req, 0, NULL, NULL);
>
> sg_init_table(desc.infrags, 4);
> sg_init_table(desc.outfrags, 4);
>
> err = xdr_process_buf(buf, offset + GSS_KRB5_TOK_HDR_LEN,
> cbcbytes, encryptor, &desc);
> skcipher_request_zero(req);
> if (err)
> goto out_err;
> }
>
> /* Make sure IV carries forward from any CBC results. */
> err = gss_krb5_cts_crypt(cipher, buf,
> offset + GSS_KRB5_TOK_HDR_LEN + cbcbytes,
> desc.iv, pages, 1);
> if (err) {
> err = GSS_S_FAILURE;
> goto out_err;
> }
next prev parent reply other threads:[~2020-12-04 15:47 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 [this message]
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
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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