linux-kernel - Re: [PATCH v2 0/5] crypto: add algif

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Message-ID: <1445987716.3405.127.camel@infradead.org>
Date:	Wed, 28 Oct 2015 08:15:16 +0900
From:	David Woodhouse <dwmw2@...radead.org>
To:	Stephan Mueller <smueller@...onox.de>
Cc:	Marcel Holtmann <marcel@...tmann.org>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	linux-crypto@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-api@...r.kernel.org, David Howells <dhowells@...hat.com>
Subject: Re: [PATCH v2 0/5] crypto: add algif_akcipher user space API

On Tue, 2015-10-27 at 11:50 +0100, Stephan Mueller wrote:
> 
> >expose that critically limited API to userspace. We need to expose an
> >API which supports hardware keys, and basically that means using the
> >kernel's key subsystem.
> 
> Agreed. But at the same time, that interface should be able to support the use 
> case where the software wants to be in control (just take OpenSSL as the 
> simple example where you can add an engine for the Linux kernel backed RSA 
> operation).

Absolutely. The interface needs to support *both*.

I've spent a lot of time chasing through userspace stacks, fixing
broken assumptions that we will *always* have the actual key material
in a file — and making libraries and applications accept PKCS#11 URIs
referring to keys in hardware as well as filenames.

I am violently opposed to exposing an API from the kernel which makes
that *same* fundamental mistake, and ties its users to using *only*
software keys.

FROM THE BEGINNING, users of this new API should be able to cope with
the fact that they might not *have* the key material, and that they
might simply be referring to a key which exists elsewhere. Such as in
the TPM, or within an SGX software enclave.

-- 
dwmw2

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