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Posted By

weilawei on 05/09/12


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code message hash authentication hmac hashed


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HMAC

 / Published in: Python
 

HMAC, pass a hash from Crypto.Hash in PyCrypto. Key should be a bytes object. Returns a bytearray.

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  1. def pad_key(a_hash, a_key):
  2.     block_size = a_hash.digest_size
  3.  
  4.     if (len(a_key) > block_size):
  5.         a_hasher = a_hash.new()
  6.         a_hash.update(a_key)
  7.         return a_hasher.digest()
  8.     elif (len(a_key) < block_size): 
  9.         return a_key + (b'\x00' * (block_size - len(a_key)))
  10.  
  11.     return a_key
  12.  
  13. def HMAC(a_hash, a_key, data):
  14.     block_size  = a_hash.digest_size
  15.     a_key       = pad_key(a_hash, a_key)
  16.     block_range = bytearray([i for i in range(block_size)])
  17.     xor_5c      = bytearray.maketrans(block_range, bytearray([i ^ 0x5c for i in range(block_size)]))
  18.     xor_36      = bytearray.maketrans(block_range, bytearray([i ^ 0x36 for i in range(block_size)]))
  19.  
  20.     inner_hasher = a_hash.new()
  21.     outer_hasher = inner_hasher.copy()
  22.     final_hasher = inner_hasher.copy()
  23.  
  24.     inner_hasher.update(a_key.translate(xor_36) + data)
  25.     outer_hasher.update(a_key.translate(xor_5c) + inner_hasher.digest())
  26.     final_hasher.update(outer_hasher.digest())
  27.  
  28.     return bytearray(final_hasher.digest())

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