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Date:   Thu, 13 Dec 2018 18:12:33 +0800
From:   Herbert Xu <herbert@gondor.apana.org.au>
To:     Vitaly Chikunov <vt@altlinux.org>
Cc:     dhowells@redhat.com, davem@davemloft.net, keyrings@vger.kernel.org,
        linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH] akcipher: Introduce verify2 for public key algorithms
Message-ID: <20181213101233.6t7d5mxxkkavo46h@gondor.apana.org.au>
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Vitaly Chikunov <vt@altlinux.org> wrote:
> Current akcipher .verify() just decrypts signature to uncover message
> hash, which is then verified in upper level public_key_verify_signature
> by memcmp with the expected signature value, which is never passed into
> verify().
> 
> This approach is incompatible with ECDSA algorithms, because, to verify
> a signature ECDSA algorithm also needs a hash value as input; also, hash
> is used in ECDSA (together with a signature divided into halves `r||s`),
> not to produce hash, but to produce a number, which is then compared to
> `r` (first part of the signature) to determine if the signature is
> correct.  Thus, for ECDSA, nor requirements of .verify() itself, nor its
> output expectations in public_key_verify_signature aren't satisfied.
> 
> Make alternative .verify2() call which gets hash value and produce
> complete signature check (without any output, thus max_size() call will
> not be needed for verify2() operation).
> 
> If .verify2() call is present, it should be used in place of .verify().
> 
> Signed-off-by: Vitaly Chikunov <vt@altlinux.org>

We should convert all existing users to this interface and not
have both verify/verify2 forever.

Thanks,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt