On Tuesday, December 9, 2014 10:12:09 AM UTC-5, Jean-Pierre Münch wrote:
>
>
>
> Am Dienstag, 9. Dezember 2014 02:29:30 UTC+1 schrieb James Kelvin:
>>
>> Thank you very much for your Threefish implementation. 
>>
>> However it doesn't work as I expected . 
>>
>> I have encountered a problem with key size. Regarding specification: Key 
>> sizes are 256, 512 or 1024 bits (key size is equal to block size). 
>>
>> For example - your implementation of 1024bit version refuses 128B key and 
>> demands 144B (1152bit): 
>> /struct Threefish1024_Info : public *FixedKeyLength<144>*, public 
>> FixedBlockSize<128>, public FixedRounds<80>/ 
>> ...
>>
> You might or might not know that Threefish normally accepts 4 Parameters: 
> Key- (and Block-)size, Key, IV (if any) and Tweak.
> As there's no standard in Crypto++ concerning tweakable blockciphers (to 
> which Threefish belongs) I took the standard I found and did my best to 
> integrate Threefish into it.
>
You might want to look at the way Crypto++ provides an interface into 
authenticated encryption modes like EAX, CCM and GCM. Authenticated 
encryption modes allow variable length authentication tags, and that does 
not seem too different than the tweak on tweakable modes like OCB and 
Threefish.

Jeff 

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