p:hash : add CRC

Even if sha and md5 are very strong, weak use are still in place in V42,
Ethernet, FDDI, ZIP and PNG

They all use a CRC

I think we should allow a new value for algorithm 'crc' with three
parameters provided on 'parameters' port :

* size in bits (integer)
* polynom as a String (or hexBinary)
* polynom-form as a string amongst ("Normal", "Reverse" or
'NormalOfReciprocal")

Option 1 : we could say there is no default so you need to provide the
parameters
Option 2 : we could say that if no parameters are provided, then it will be
defaulted to size=32, polynom=0xEDB88320 and polynom-form=Reverse (which is
CRC-32-IEEE 802.3 used in V42, MPEG 2 and PNG)

Regards,

Mohamed




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