linux-kernel - Re: [PATCH] crypto: ccree: fix iv copying for small buffers

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Message-ID: <CAOtvUMcChKswKBCOkN7DGvK3DcotJBh0y=-Xi8232uYK26-xQA@mail.gmail.com>
Date:   Thu, 21 Jun 2018 16:35:44 +0300
From:   Gilad Ben-Yossef <gilad@...yossef.com>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Hadar Gat <hadar.gat@....com>, Ofir Drang <ofir.drang@....com>,
        stable@...r.kernel.org,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        Linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] crypto: ccree: fix iv copying for small buffers

On Tue, Jun 19, 2018 at 5:27 PM, Herbert Xu <herbert@...dor.apana.org.au> wrote:
> On Sun, Jun 17, 2018 at 01:06:42PM +0300, Gilad Ben-Yossef wrote:
>>
>> It was ctr(aes). I wrongly assumed that we are supposed to unconditionally
>> copy
>> the cipher-text block post operation and let the caller do with it what it
>> wants and so the
>> code now does that for all cipher operations unconditionally.
>
> For CTR it doesn't matter whether the last block is less than a
> block, you should still increment the counter.

OK. got it. Although I am not sure how does one use this to continue
encryption if the plaintext was not block aligned.
>

>> So what is a good description of what we are supposed to provide in that
>> field post operation?
>> The next IV? but as you stated, that is not necessarily useful for all
>> ciphers.
>
> When in doubt, please refer to the generic implementation.  If
> that is still unclear or if it seems wrong, please post to the
> list.


Got it.

So as a sanity check  if I understood correctly I need to:
- Increment counter in IV for CTS
- Copy last ciphertext block for CFB and CBC to output IV (partial
blocks not allowed)

What about OFB? unless I've missed something there is no generic
implementation... ?


Thanks again,
Gilad

-- 
Gilad Ben-Yossef
Chief Coffee Drinker

values of β will give rise to dom!