[email protected] (Niels Möller) writes:

>> Maybe throw an error for non-16/24/32 key sizes?  I'm not sure how
>> useful it is to support that.
>
> Not terribly useful, I guess, but since it's well defined by the serpent
> spec, I think it should be supported.

Which spec?  According to wikipedia

https://secure.wikimedia.org/wikipedia/en/wiki/Serpent_%28cipher%29

this is the official serpent homepage:

http://www.cl.cam.ac.uk/~rja14/serpent.html

and the link for "algorithm specification" is

http://www.cl.cam.ac.uk/~rja14/Papers/serpent.pdf

which says that 

   The user key length is variable, but for the purposes of this
   submission we fix it at 128, 192 or 256 bits

That is a bit vague, either it is variable or it isn't.

The Serpent-0 specification says

   The user key can be of any length between 64 and 256 bits.[5]

   [5] We define key lengths to be multiples of 32 bits for ease of
   implementation, and ...

Thus in any case, it seems, the key size is not completely variable and
always a multiple of 32 bits (which resolves the key alignment issue).

My impression is that Serpent is a bit confusingly specified, and it is
unclear which specification is actually the right one.  The test vector
confusion reinforced my impression here.

/Simon
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