linux-kernel - Re: [PATCH v6 3/6] crypto: AF_ALG -- add asymmetric cipher interface

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Date:	Thu, 23 Jun 2016 07:07:05 +0200
From:	Stephan Mueller <smueller@...onox.de>
To:	Mat Martineau <mathew.j.martineau@...ux.intel.com>
Cc:	Tadeusz Struk <tadeusz.struk@...el.com>, dhowells@...hat.com,
	herbert@...dor.apana.org.au, linux-api@...r.kernel.org,
	marcel@...tmann.org, linux-kernel@...r.kernel.org,
	keyrings@...r.kernel.org, linux-crypto@...r.kernel.org,
	dwmw2@...radead.org, davem@...emloft.net
Subject: Re: [PATCH v6 3/6] crypto: AF_ALG -- add asymmetric cipher interface

Am Mittwoch, 22. Juni 2016, 15:45:38 schrieb Mat Martineau:

Hi Mat,

> > 
> > Ok, I'll update the patch.
> 
> Thanks, that helps (especially with pkcs1pad).

Tadeusz received the updated patch from me to integrate it into his patch set.
> 
> This brings me to another proposal for read buffer sizing: AF_ALG akcipher
> can guarantee that partial reads (where the read buffer is shorter than
> the output of the crypto op) will work using the same semantics as
> SOCK_DGRAM/SOCK_SEQPACKET. With those sockets, as much data as will fit is
> copied in to the read buffer and the remainder is discarded.
> 
> I realize there's a performance and memory tradeoff, since the crypto
> algorithm needs a sufficiently large output buffer that would have to be
> created by AF_ALG akcipher. The user could manage that tradeoff by
> providing a larger buffer (typically key_size?) if it wants to avoid
> allocating and copying intermediate buffers inside the kernel.

How shall the user know that something got truncated or that the kernel 
created memory?

Ciao
Stephan