[FFmpeg-devel] libavutil: added camellia block cipher

Giorgio Vazzana mywing81 at gmail.com
Sat Dec 27 17:25:04 CET 2014


Hi,

2014-12-24 23:41 GMT+01:00 supraja reddy <supraja0493 at gmail.com>:
> Hello,
>
> Thank you for your reviews. I have attached the updated patch .
>
> You are using a single array K for all the keys, without distinguishing
>> between
>> kw, k and ke as in the rfc. This makes code harder to read/maintain with no
>> real gain I guess. Any reason why you made this decision?
>>
>
> I have created a single array for all keys to make the key scheduling more
> compact as you have seen. Please let me know if there is any other way to
> do so .

You can separate the keys and still make the scheduling compact by
using a single for loop to compute the 24 k subkeys, and then compute
kw and ke. This will probably also simplify the encrypt() and
decrypt() functions.

>>
>> > +    Zl ^= ((Zr << 8) | (Zr >> 24));
>> > +    Zr ^= ((Zl << 16) | (Zl >> 16));
>> > +    Zl ^= ((Zr >> 8) | (Zr << 24));
>> > +    Zr ^= ((Zl >> 8) | (Zl << 24));
>>
>> This optimization is correct, just curious, where did you read about it?
>>
>
> I have found a specifications page for camellia by the authors of the
> algorithm. Here's the link to it :
> www.cryptrec.go.jp/cryptrec_03_spec_cypherlist_files/PDF/06_01espec.pdf
> I hope I am allowed to do so.

Of course, you are encouraged to read other material/documentation and
compare/improve your implementation of the algorithm.

>Please let me know if you find anything
> useful in the above link that I can incorporate.

There are other useful optimizations described in that paper, but we
can implement them later.

>
> Please let me know if there are any further changes.
>
> Thanks,
>
> Supraja
>
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