linux-kernel - Re: [PATCH v8 03/10] crypto: akcipher - new verify API for public key algorithms

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Date:   Tue, 26 Mar 2019 11:00:40 -0500
From:   Denis Kenzior <denkenz@...il.com>
To:     Vitaly Chikunov <vt@...linux.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        David Howells <dhowells@...hat.com>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        linux-integrity@...r.kernel.org, keyrings@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 03/10] crypto: akcipher - new verify API for public key
 algorithms

Hi Vitaly,

On 03/26/2019 07:58 AM, Vitaly Chikunov wrote:
> Previous akcipher .verify() just `decrypts' (using RSA encrypt which is
> using public key) signature to uncover message hash, which was then
> compared in upper level public_key_verify_signature() with the expected
> hash value, which itself was never passed into verify().
> 
> This approach was incompatible with EC-DSA family of algorithms,
> because, to verify a signature EC-DSA algorithm also needs a hash value
> as input; then it's used (together with a signature divided into halves
> `r||s') to produce a witness value, which is then compared with `r' to
> determine if the signature is correct. Thus, for EC-DSA, nor
> requirements of .verify() itself, nor its output expectations in
> public_key_verify_signature() wasn't sufficient.
> 
> Make improved .verify() call which gets hash value as input and produce
> complete signature check without any output besides status.
> 
> Now for the top level verification only crypto_akcipher_verify() needs
> to be called and its return value inspected.
> 
> Make sure that `digest' is in kmalloc'd memory (in place of `output`) in
> {public,tpm}_key_verify_signature() as insisted by Herbert Xu, and will
> be changed in the following commit.
> 
> Cc: David Howells <dhowells@...hat.com>
> Cc: keyrings@...r.kernel.org
> Signed-off-by: Vitaly Chikunov <vt@...linux.org>
> ---
>   crypto/asymmetric_keys/asym_tpm.c   | 34 ++++++++-----------------
>   crypto/asymmetric_keys/public_key.c | 34 ++++++++-----------------
>   crypto/rsa-pkcs1pad.c               | 29 +++++++++++++--------
>   crypto/testmgr.c                    | 50 ++++++++++++++++++++++---------------
>   include/crypto/akcipher.h           | 36 ++++++++++++++++----------
>   5 files changed, 92 insertions(+), 91 deletions(-)

The TPM bits, public_key and akcipher changes look good to me.  Didn't 
look into testmgr.

Feel free to add
Reviewed-by: Denis Kenzior <denkenz@...il.com>

to this and patch 4.

Regards,
-Denis