linux-kernel - Re: [RFC 1/1] ima: digital signature verification using asymmetric keys

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Date:	Mon, 28 Jan 2013 17:20:20 +0200
From:	"Kasatkin, Dmitry" <dmitry.kasatkin@...el.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Mimi Zohar <zohar@...ux.vnet.ibm.com>, dhowells@...hat.com,
	jmorris@...ei.org, linux-security-module@...r.kernel.org,
	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 1/1] ima: digital signature verification using asymmetric keys

On Mon, Jan 28, 2013 at 5:15 PM, Vivek Goyal <vgoyal@...hat.com> wrote:
> On Mon, Jan 28, 2013 at 04:54:06PM +0200, Kasatkin, Dmitry wrote:
>> On Fri, Jan 25, 2013 at 11:01 PM, Vivek Goyal <vgoyal@...hat.com> wrote:
>> > Hi,
>> >
>> > I am trying to read and understand IMA code. How does digital signature
>> > mechanism work.
>> >
>> > IIUC, evmctl will install a file's signature in security.ima. And later
>> > process_measurement() will do following.
>> >
>> > Calculate digest of file in ima_collect_measurement() and then
>> > ima_appraise_measurement() actually compares signatuer against the
>> > digest.
>> >
>> > If yes, ima_collect_measurement() always calculates digest either using
>> > md5/sha1 but signatures might have used sha256 or something else. So
>> > how does it work. What am I missing.
>>
>> Hi,
>>
>> Yes, currently it is possible to use only single configured algorithm, which is
>> in generally enough. Consider it like a policy.
>> Soon it will be a patch which allows to use any hash algorithms, supported by
>> asymmetric key verification API.
>
> Ok. I am hoping that it will be more than the kernel command line we
> support. In the sense that for digital signatures one needs to parse
> the signature, look at what hash algorithm has been used  and then
> collect the hash accordingly. It is little different then IMA requirement
> of calculating one pre-determine hash for all files.

Yes... It is obvious. It's coming.
But in general, signer should be aware of requirements and limitation
of the platform.
It is not really a problem...

- Dmitry

>
> Thanks
> Vivek
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