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From:   Stephan Mueller <smueller@chronox.de>
To:     Anshuman Gupta <anshuman.gupta@intel.com>
Cc:     linux-crypto@vger.kernel.org
Subject: Re: [Query] RSA SHA-384 signature verification
Date:   Tue, 16 Jun 2020 07:03:28 +0200
Message-ID: <13970611.Hd4P73xESc@tauon.chronox.de>
In-Reply-To: <20200616035603.GG14085@intel.com>
References: <20200615170413.GF14085@intel.com> <1730161.mygNopSbl3@tauon.chronox.de> <20200616035603.GG14085@intel.com>
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Am Dienstag, 16. Juni 2020, 05:56:04 CEST schrieb Anshuman Gupta:

Hi Anshuman,

> On 2020-06-15 at 21:25:58 +0200, Stephan Mueller wrote:
> > Am Montag, 15. Juni 2020, 19:04:14 CEST schrieb Anshuman Gupta:
> > 
> > Hi Anshuman,
> > 
> > > Hi ,
> > > I wanted to verify a RSA SHA-384 signature.
> > > I am using crypto_alloc_shash(), crypto_shash_digest() API to extract
> > > the SHA-384 digest.
> > > I am having public key along with the sha-384 digest extracted from raw
> > > data and signature. AFAIU understand from crypto documentation that i
> > > need to verify the signature by importing public key to
> > > akcipher/skcipher API. Here i am not sure which cipher API to prefer
> > > symmetric key cipher or asymmetric key cipher API.
> > > 
> > > There are two types of API to import the key.
> > > crypto_skcipher_setkey()
> > > crypto_akcipher_set_pub_key()
> > > 
> > > Also i am not sure exactly which algo to use for RSA-SHA384 signature
> > > verification.
> > > 
> > > Any help or inputs from crypto community will highly appreciated.
> > 
> > akcipher: asymmetric key crypto
> > 
> > skcipher: symmetric key crypto
> 
> Many thanks for your input, based upon your inputs i should use
> akcipher.
> Actually tried to grep crypto_akcipher_set_pub_key() but there are not any
> usages of this API in Linux drivers.
> What is the preferred method to verify a RSA signature inside any Linux
> GPL driver, is there any standard interface API to verify RSA signature
> by importing input of raw data and public key or else
> it is recommended method to use below set low level of API
> crypto_alloc_akcipher(), akcipher_request_alloc(),
> akcipher_request_set_crypt(), crypto_akcipher_verify().

You can use that API directly or you can go through the intermediary of the 
crypto/asymmetric_keys API. One use case is the kernel signature verification 
as implemented in kernel/module_signing.c

> Thanks,
> Anshuman.
> 
> > > Thanks ,
> > > Anshuman Gupta.
> > 
> > Ciao
> > Stephan


Ciao
Stephan