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SubjectRe: [PATCH v3 5/7] crypto: AF_ALG: add random number generator support
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 <smueller@chronox.de>

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 <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt


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