From: Harsh Jain Subject: Re: Who will copy the AAD data to dest. buffer Date: Sat, 3 Sep 2016 10:45:08 +0530 Message-ID: References: <20160902144203.GA13135@gondor.apana.org.au> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Cc: linux-crypto@vger.kernel.org, Stephan Mueller To: Herbert Xu Return-path: Received: from mail-oi0-f42.google.com ([209.85.218.42]:36774 "EHLO mail-oi0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751468AbcICFPJ (ORCPT ); Sat, 3 Sep 2016 01:15:09 -0400 Received: by mail-oi0-f42.google.com with SMTP id w78so341714oie.3 for ; Fri, 02 Sep 2016 22:15:09 -0700 (PDT) In-Reply-To: <20160902144203.GA13135@gondor.apana.org.au> Sender: linux-crypto-owner@vger.kernel.org List-ID: Thanks Herbert for clarification. It means Libkcapi documentation needs update of chapter "Aead Cipher API". Regards Harsh Jain On Fri, Sep 2, 2016 at 8:12 PM, Herbert Xu wrote: > On Fri, Sep 02, 2016 at 08:05:04PM +0530, Harsh Jain wrote: >> Hi Herbert, >> >> Is copy of AAD data to destination buffer when dst != src is mandatory >> requirements for crypto drivers or we can skip this copy. Actually I >> am bit confused, In following link Stephen had mentioned caller will >> memcpy the AAD to destination buffer but authenc.c also copies the AAD >> to dest. buffer. >> >> http://www.chronox.de/libkcapi/html/ch02s02.html > > It has to be copied if src != dst. > >> Secondly When AAD data remains unchanged in AEAD encryption/decryption >> operations. Why we copy the same data to destination buffer? > > This greatly simplifies the implementation of the AEAD algorithms > because we can throw away src and use the dst only. For example, > authenc hashes the AAD and ciphertext. If we didn't force the > copy it would have to hash them separately, meaning the use of > the slow init/update/final interface. With the copy it can use > the digest interface. > > Cheers, > -- > Email: Herbert Xu > Home Page: http://gondor.apana.org.au/~herbert/ > PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt