[Cryptography] updating a counter

[dj at deadhat.com]

>> My favorite thing is to use a collection of subcounters.
>>
>> Most of the subcounters are LFSRs.  Some of them shift
>> left, and some of them shift right.  Between the shifting
>> and the XORing, a lot of bits get changed.
>
> Or you could just use CRC32 or CRC64, adding a bit to the CRC checked
> message instead of adding 1 to the equivalent counter. You will get to
> change half the bits in the counter for each message, and you will have a
> long enough non repeat period.
>
> -- Christian Huitema
>

I personally like *3 in the GF(2**n) field of your choice (a shift + xor +
xor poly on overflow). Guaranteed maximal length. Simple to work out for
any n. Is less boring than CRCx and doesn't involve the silly bit
reordering and inversion of the CCITT CRCs.