From: Herbert Xu Subject: Re: [PATCH v3 5/7] crypto: AF_ALG: add random number generator support Date: Mon, 24 Nov 2014 22:31:50 +0800 Message-ID: <20141124143150.GC31469@gondor.apana.org.au> References: <4088013.2O8zCP0xXa@tachyon.chronox.de> <2490914.nzfN9gyyGH@tachyon.chronox.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Daniel Borkmann , 'Quentin Gouchet' , lkml - Kernel Mailing List , linux-crypto@vger.kernel.org, linux-api@vger.kernel.org To: Stephan Mueller Return-path: Received: from helcar.apana.org.au ([209.40.204.226]:46964 "EHLO helcar.apana.org.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751839AbaKXOb6 (ORCPT ); Mon, 24 Nov 2014 09:31:58 -0500 Content-Disposition: inline In-Reply-To: <2490914.nzfN9gyyGH@tachyon.chronox.de> Sender: linux-crypto-owner@vger.kernel.org List-ID: On Fri, Nov 21, 2014 at 06:32:52AM +0100, Stephan Mueller wrote: > This patch adds the random number generator support for AF_ALG. > > A random number generator's purpose is to generate data without > requiring the caller to provide any data. Therefore, the AF_ALG > interface handler for RNGs only implements a callback handler for > recvmsg. > > The following parameters provided with a recvmsg are processed by the > RNG callback handler: > > * sock - to resolve the RNG context data structure accessing the > RNG instance private to the socket > > * len - this parameter allows userspace callers to specify how > many random bytes the RNG shall produce and return. As the > kernel context for the RNG allocates a buffer of 128 bytes to > store random numbers before copying them to userspace, the len > parameter is checked that it is not larger than 128. If a > caller wants more random numbers, a new request for recvmsg > shall be made. > > The size of 128 bytes is chose because of the following considerations: > > * to increase the memory footprint of the kernel too much (note, > that would be 128 bytes per open socket) > > * 128 is divisible by any typical cryptographic block size an > RNG may have > > * A request for random numbers typically only shall supply small > amount of data like for keys or IVs that should only require > one invocation of the recvmsg function. > > Note, during instantiation of the RNG, the code checks whether the RNG > implementation requires seeding. If so, the RNG is seeded with output > from get_random_bytes. > > A fully working example using all aspects of the RNG interface is > provided at http://www.chronox.de/libkcapi.html > > Signed-off-by: Stephan Mueller Sorry but who is going to use this and for what purpose? Every other algif interface exports real hardware features that cannot otherwise be accessed from user-space. All crypto RNGs are by definition software-only, so what is the point of this? Cheers, -- Email: Herbert Xu Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt