GenericCRC

A generic CRC implementation in Python, which supports arbitrary CRC sizes.

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Class GenericCRC is a generic CRC implementation supporting arbitrary CRC sizes (>=8) and parametrization.

Usage

Use Generic CRC in 2 steps:

1. Construct a GenericCRC object. The construction of GenericCRC:
   
   

   GenericCRC(name, crcLen, poly, initCRC=0, refin=False, refout=False, xorout=0)
   

   • name: The name of the CRC. Informative, not used by CRC calculation.
   • crcLen: Size of the CRC. For example, 32 for CRC32
   • poly: The normal representation of the generation polynomial of the CRC
   • initCRC: The value used to initialize the CRC value / register
   • refin: If this value is True, each input byte is reflected before being used in the calculation. Reflected means that the bits of the input byte are used in reverse order.
   • refout: If this value is True, the final CRC value is reflected before being returned. The reflection is done over the whole CRC value.
   • xorout: This value is xored to the final CRC value before being returned. For example, to calculate CRC32C:
     

   crc32c = GenericCRC("CRC32C", crcLen=32, poly=0x1EDC6F41, initCRC=0xFFFFFFFF, refin=True, refout=True, xorout=0xFFFFFFFF)<br>
   

2. Call the object's Calculate() method on the message whose CRC is to be calculated. For example, to calculate CRC32C for messeage "Hello, World!":
   

   msg = "Hello, World".encode('utf-8')
   crc = crc32c.Calculate(msg)
   

Note, the method Calculate expects an input of bytes or bytearray type.
You can also call the Check() method to see the check value of the constructed CRC object. The check value is the CRC value of input string "123456789" encoded in utf-8.

Sanity Check

GenericCRC.py has sanity checks. Directly run "python GenericCRC.py" to see the test results. All test vectors are from https://reveng.sourceforge.io/crc-catalogue/all.htm
After constructing a CRC object, you can also call its Check() method to see the CRC digest of string "123456789" as a sanity check.