Here is some code to check the CRC of a given message. The result of 0 indicates no trouble found. Reference: http://www.ross.net/crc/download/crc_v3.txt
Code:
def checkCRC(message):
#CRC-16-CITT poly, the CRC sheme used by ymodem protocol
poly = 0x1021
#16bit operation register, initialized to zeros
reg = 0x0000
#pad the end of the message with the size of the poly
message += '\x00\x00'
#for each bit in the message
for byte in message:
mask = 0x80
while(mask > 0):
#left shift by one
reg<<=1
#input the next bit from the message into the right hand side of the op reg
if ord(byte) & mask:
reg += 1
mask>>=1
#if a one popped out the left of the reg, xor reg w/poly
if reg > 0xffff:
#eliminate any one that popped out the left
reg &= 0xffff
#xor with the poly, this is the remainder
reg ^= poly
return reg