netdev - Re: [PATCH net-next] net/tls: Add support of AES128-CCM based ciphers

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Date:   Tue, 19 Mar 2019 17:06:22 +0000
From:   Boris Pismenny <borisp@...lanox.com>
To:     Vakul Garg <vakul.garg@....com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     Aviad Yehezkel <aviadye@...lanox.com>,
        "davejwatson@...com" <davejwatson@...com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "doronrk@...com" <doronrk@...com>
Subject: Re: [PATCH net-next] net/tls: Add support of AES128-CCM based ciphers


On 3/19/2019 7:15 AM, Vakul Garg wrote:
> Added support for AES128-CCM based record encryption. AES128-CCM is
> similar to AES128-GCM. Both of them have same salt/iv/mac size. The
> notable difference between the two is that while invoking AES128-CCM
> operation, the salt||nonce (which is passed as IV) has to be prefixed
> with a hardcoded value '2'. Further, CCM implementation in kernel
> requires IV passed in crypto_aead_request() to be full '16' bytes.
> Therefore, the record structure 'struct tls_rec' has been modified to
> reserve '16' bytes for IV. This works for both GCM and CCM based cipher.
> 

Can you explain what is the source of the hardcoded '2'? e.g. Why do we 
need a hardcoded constant?