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From: Andrzej Kaczmarek <andrzej.kaczmarek@tieto.com>
Date: Wed, 14 May 2014 17:25:04 +0200
Message-ID: <CAF3PWx3Bte2G-PbRCYfQAOMOyi1RcszpW-U4qBHUayiVvLKNyg@mail.gmail.com>
Subject: Re: [PATCH 2/3] shared/crypto: Add support to sign data with AES-CMAC
To: Marcel Holtmann <marcel@holtmann.org>
Cc: Lukasz Rymanowski <lukasz.rymanowski@tieto.com>,
	linux-bluetooth <linux-bluetooth@vger.kernel.org>
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List-ID: <linux-bluetooth.vger.kernel.org>

Hi Marcel,

On 14 May 2014 17:07, Marcel Holtmann <marcel@holtmann.org> wrote:
> Hi Lukas,
>
>> This patch adds support to generate hash using AES-CMAC algorithm
>> ---
>> src/shared/crypto.c | 37 +++++++++++++++++++++++++++++++++++++
>> src/shared/crypto.h |  4 ++++
>> 2 files changed, 41 insertions(+)
>>
>> diff --git a/src/shared/crypto.c b/src/shared/crypto.c
>> index f0b2979..a0bcc7b 100644
>> --- a/src/shared/crypto.c
>> +++ b/src/shared/crypto.c
>> @@ -256,6 +256,43 @@ static inline void swap128(const uint8_t src[16], uint8_t dst[16])
>>               dst[15 - i] = src[i];
>> }
>>
>> +bool bt_crypto_cmac_aes_hash(struct bt_crypto *crypto,
>> +                                     const uint8_t key[16],
>> +                                     const uint8_t *m, uint16_t m_len,
>> +                                     uint8_t hash[12])
>> +{
>> +     int fd;
>> +     int len;
>> +     uint8_t tmp[16], out[16];
>> +
>> +     if (!crypto)
>> +             return false;
>> +
>> +     /* The most significant octet of key corresponds to key[0] */
>> +     swap128(key, tmp);
>> +
>> +     fd = alg_new(crypto->cmac_aes, tmp, 16);
>> +     if (fd < 0)
>> +             return false;
>> +
>> +     len = send(fd, m, m_len, 0);
>> +     if (len < 0)
>> +             return false;
>> +
>> +     len = read(fd, out, 16);
>> +     if (len < 0)
>> +             return false;
>> +
>> +     /*
>> +      * The most significant octet of hash corresponds to out[0]  - swap it.
>> +      * Then truncate in most significant bit first order to a length of
>> +      * 12 octets
>> +      */
>> +     swap128(out, tmp);
>> +     memcpy(hash, tmp + 4, 12);
>> +
>> +     return true;
>> +}
>> /*
>>  * Security function e
>>  *
>> diff --git a/src/shared/crypto.h b/src/shared/crypto.h
>> index cae8daa..05888b9 100644
>> --- a/src/shared/crypto.h
>> +++ b/src/shared/crypto.h
>> @@ -46,3 +46,7 @@ bool bt_crypto_c1(struct bt_crypto *crypto, const uint8_t k[16],
>> bool bt_crypto_s1(struct bt_crypto *crypto, const uint8_t k[16],
>>                       const uint8_t r1[16], const uint8_t r2[16],
>>                       uint8_t res[16]);
>> +bool bt_crypto_cmac_aes_hash(struct bt_crypto *crypto,
>> +                                     const uint8_t key[16],
>> +                                     const uint8_t *m, uint16_t m_len,
>> +                                     uint8_t hash[12]);
>
> we are using the cryptographic names from the Bluetooth specification cryptographic toolbox. I bet this one has a proper function name as well. So lets use that one.

Actually it does not have other name - AES-CMAC is referenced in
section "2.4.5 Signing algorithm" of SMP specification as algorithm to
be used for signing. Perhaps we can call it 'bt_crypto_le_sign' since
it's used for signing LE data (as per spec) or just leave as-is.

BR,
Andrzej