linux-kernel - Re: [PATCH 08/21] KEYS: Add signature verification facility [ver #3]

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Date:	Wed, 18 Jan 2012 15:26:05 +0200
From:	"Kasatkin, Dmitry" <dmitry.kasatkin@...el.com>
To:	David Howells <dhowells@...hat.com>
Cc:	keyrings@...ux-nfs.org, linux-crypto@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org, zohar@...ux.vnet.ibm.com,
	arjan.van.de.ven@...el.com, alan.cox@...el.com
Subject: Re: [PATCH 08/21] KEYS: Add signature verification facility [ver #3]

On Wed, Jan 18, 2012 at 2:26 PM, David Howells <dhowells@...hat.com> wrote:
> Kasatkin, Dmitry <dmitry.kasatkin@...el.com> wrote:
>
>> It would also nice to have an API to supply pre-computed data hash.  For
>> example IMA uses the same functionality to compute the hash of the file
>> content, and then, based on security.ima type decided either verify it using
>> just hash, or use digital signature.  We could pass a hash as data. But may
>> be we do not want to have extra operation and compute hash over hash.
>
> If I understand you correctly, you'd like to have the option to do the hashing
> externally to this API?  Would you supply the completed hash or just a hash
> with the data in it, and require this API to complete it (ie. chuck metadata
> into it)?
>

I meant just a hash of data..
Right, I remember, PGP finalizes hash with some additional metadata
pgp_pkey_digest_signature() seems does it...


> I don't think it should be hard.  I could add an alternative to
> verify_sig_add_data() perhaps.  Either that or one function that does the lot
> and takes the precomputed hash as input.  There would be no need for the split
> into four functions (begin, add_data, end, cancel) in such a case.  The reason
> for the split is so that the caller can invoke add_data several times with
> non-contiguous bits of data.
>

Yes. it is clear...
Would it be possible to have pass data (uncompleted) hash?


> It might even make sense to expose the crypto hash object for direct access
> rather than use add_data - but that then makes it hard to use crypto hardware
> where you would just shovel the raw data into it and it does all the hashing
> and cryptography in a black box.
>
> David
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