From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A336BC0018C for ; Fri, 4 Dec 2020 15:47:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4EE9B22BEF for ; Fri, 4 Dec 2020 15:47:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730596AbgLDPrH (ORCPT ); Fri, 4 Dec 2020 10:47:07 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49382 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726427AbgLDPrH (ORCPT ); Fri, 4 Dec 2020 10:47:07 -0500 Received: from fieldses.org (fieldses.org [IPv6:2600:3c00:e000:2f7::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0C104C061A52; Fri, 4 Dec 2020 07:46:27 -0800 (PST) Received: by fieldses.org (Postfix, from userid 2815) id 084D96F73; Fri, 4 Dec 2020 10:46:26 -0500 (EST) DKIM-Filter: OpenDKIM Filter v2.11.0 fieldses.org 084D96F73 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fieldses.org; s=default; t=1607096786; bh=wHiljjMIkY8nl/ZnPYa+9FcyCXYDIXfFUmp0/iytMrM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=jTPxHvE/rGumvGlYaM+xc80ODgvFi/CXOAPyE56Pd0+nQhVPHOXFK7EhdOBinOa3w LrUc+fa/1stZlpjT2QV+/OO2Ze/68TbyZoZBkhon+I4vAfX+PbuUS0sWT9pcimjm9x 9vqFoS4izZ03kMWkuY7cWfCH4jd08F1FWv66Hfr4= Date: Fri, 4 Dec 2020 10:46:26 -0500 From: Bruce Fields To: David Howells Cc: Chuck Lever , CIFS , Linux NFS Mailing List , Herbert Xu , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Trond Myklebust , 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? Message-ID: <20201204154626.GA26255@fieldses.org> References: <2F96670A-58DC-43A6-A20E-696803F0BFBA@oracle.com> <160518586534.2277919.14475638653680231924.stgit@warthog.procyon.org.uk> <118876.1607093975@warthog.procyon.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <118876.1607093975@warthog.procyon.org.uk> User-Agent: Mutt/1.5.21 (2010-09-15) Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org 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; > }