Thanks for the response, Jeffrey. I've now discovered that using just plain
CFB_Mode allows me to use input blocks of any size. Only the FIPS
variant imposes the size constraint.
Rereading the FIPS NIST 800-38A document, I see that it requires the input
to be a multiple of what it calls segment size. I believe segment size is
equivalent to what Crypto++ calls feed_back_size, except that segment size
is in bits while the feed_back_size parameter is in bytes. The constraint
for CFB_FIPS_Mode requires multiples of this feed_back_size, not
multiples of the block size as I thought at first. My test had
feed_back_size equal to the block size.
It all makes sense, and I guess it is not a bug. For some reason, the older
version didn't seem to enforce this constraint, not sure why.
In my system I will have to use plain CFB_Mode, can't have the assert() in
CFB_FIPS_Mode crash the whole application.
Thanks,
Joachim
On Tuesday, January 17, 2017 at 5:09:22 PM UTC-8, Jeffrey Walton wrote:
>
>
>
> On Tuesday, January 17, 2017 at 5:39:28 PM UTC-5, Joachim Achtzehnter
> wrote:
>>
>> In older versions of Crypto++, for example v5.2.3, the ProcessData()
>> function of CFB_FIPS_Mode::Decryption worked with arbitrary sizes of
>> input packets. In recent versions, at last since v5.5.2, it causes an
>> assertion if the input packet is not a multiple of the block size. CFB
>> should not require this constraint. Is this a known bug?
>>
>
> Wow, that's going back in time.
>
> Rijndael::ProcessData requires a full block size. I'm not sure what
> CFB_FIPS_Mode::ProcessData is doing at the moment. The mode can clearly
> process bytes at a time, but it should ensure a full block is being sent to
> Rijndael for processing.
>
> Do you have some sample code so I can inspect things under your setup?
>
> Jeff
>
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