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SHA-256

May 19th, 2022
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  1. """This Python module is an implementation of the SHA-256 algorithm.
  2. From https://github.com/keanemind/Python-SHA-256"""
  3.  
  4. K = [
  5.     0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
  6.     0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
  7.     0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
  8.     0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
  9.     0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
  10.     0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
  11.     0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
  12.     0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2
  13. ]
  14.  
  15. def generate_hash(message: bytearray) -> bytearray:
  16.     """Return a SHA-256 hash from the message passed.
  17.    The argument should be a bytes, bytearray, or
  18.    string object."""
  19.  
  20.     if isinstance(message, str):
  21.         message = bytearray(message, 'ascii')
  22.     elif isinstance(message, bytes):
  23.         message = bytearray(message)
  24.     elif not isinstance(message, bytearray):
  25.         raise TypeError
  26.  
  27.     # Padding
  28.     length = len(message) * 8 # len(message) is number of BYTES!!!
  29.     message.append(0x80)
  30.     while (len(message) * 8 + 64) % 512 != 0:
  31.         message.append(0x00)
  32.  
  33.     message += length.to_bytes(8, 'big') # pad to 8 bytes or 64 bits
  34.  
  35.     assert (len(message) * 8) % 512 == 0, "Padding did not complete properly!"
  36.  
  37.     # Parsing
  38.     blocks = [] # contains 512-bit chunks of message
  39.     for i in range(0, len(message), 64): # 64 bytes is 512 bits
  40.         blocks.append(message[i:i+64])
  41.  
  42.     # Setting Initial Hash Value
  43.     h0 = 0x6a09e667
  44.     h1 = 0xbb67ae85
  45.     h2 = 0x3c6ef372
  46.     h3 = 0xa54ff53a
  47.     h5 = 0x9b05688c
  48.     h4 = 0x510e527f
  49.     h6 = 0x1f83d9ab
  50.     h7 = 0x5be0cd19
  51.  
  52.     # SHA-256 Hash Computation
  53.     for message_block in blocks:
  54.         # Prepare message schedule
  55.         message_schedule = []
  56.         for t in range(0, 64):
  57.             if t <= 15:
  58.                 # adds the t'th 32 bit word of the block,
  59.                 # starting from leftmost word
  60.                 # 4 bytes at a time
  61.                 message_schedule.append(bytes(message_block[t*4:(t*4)+4]))
  62.             else:
  63.                 term1 = _sigma1(int.from_bytes(message_schedule[t-2], 'big'))
  64.                 term2 = int.from_bytes(message_schedule[t-7], 'big')
  65.                 term3 = _sigma0(int.from_bytes(message_schedule[t-15], 'big'))
  66.                 term4 = int.from_bytes(message_schedule[t-16], 'big')
  67.  
  68.                 # append a 4-byte byte object
  69.                 schedule = ((term1 + term2 + term3 + term4) % 2**32).to_bytes(4, 'big')
  70.                 message_schedule.append(schedule)
  71.  
  72.         assert len(message_schedule) == 64
  73.  
  74.         # Initialize working variables
  75.         a = h0
  76.         b = h1
  77.         c = h2
  78.         d = h3
  79.         e = h4
  80.         f = h5
  81.         g = h6
  82.         h = h7
  83.  
  84.         # Iterate for t=0 to 63
  85.         for t in range(64):
  86.             t1 = ((h + _capsigma1(e) + _ch(e, f, g) + K[t] +
  87.                    int.from_bytes(message_schedule[t], 'big')) % 2**32)
  88.  
  89.             t2 = (_capsigma0(a) + _maj(a, b, c)) % 2**32
  90.  
  91.             h = g
  92.             g = f
  93.             f = e
  94.             e = (d + t1) % 2**32
  95.             d = c
  96.             c = b
  97.             b = a
  98.             a = (t1 + t2) % 2**32
  99.  
  100.         # Compute intermediate hash value
  101.         h0 = (h0 + a) % 2**32
  102.         h1 = (h1 + b) % 2**32
  103.         h2 = (h2 + c) % 2**32
  104.         h3 = (h3 + d) % 2**32
  105.         h4 = (h4 + e) % 2**32
  106.         h5 = (h5 + f) % 2**32
  107.         h6 = (h6 + g) % 2**32
  108.         h7 = (h7 + h) % 2**32
  109.  
  110.     return ((h0).to_bytes(4, 'big') + (h1).to_bytes(4, 'big') +
  111.             (h2).to_bytes(4, 'big') + (h3).to_bytes(4, 'big') +
  112.             (h4).to_bytes(4, 'big') + (h5).to_bytes(4, 'big') +
  113.             (h6).to_bytes(4, 'big') + (h7).to_bytes(4, 'big'))
  114.  
  115. def _sigma0(num: int):
  116.     """As defined in the specification."""
  117.     num = (_rotate_right(num, 7) ^
  118.            _rotate_right(num, 18) ^
  119.            (num >> 3))
  120.     return num
  121.  
  122. def _sigma1(num: int):
  123.     """As defined in the specification."""
  124.     num = (_rotate_right(num, 17) ^
  125.            _rotate_right(num, 19) ^
  126.            (num >> 10))
  127.     return num
  128.  
  129. def _capsigma0(num: int):
  130.     """As defined in the specification."""
  131.     num = (_rotate_right(num, 2) ^
  132.            _rotate_right(num, 13) ^
  133.            _rotate_right(num, 22))
  134.     return num
  135.  
  136. def _capsigma1(num: int):
  137.     """As defined in the specification."""
  138.     num = (_rotate_right(num, 6) ^
  139.            _rotate_right(num, 11) ^
  140.            _rotate_right(num, 25))
  141.     return num
  142.  
  143. def _ch(x: int, y: int, z: int):
  144.     """As defined in the specification."""
  145.     return (x & y) ^ (~x & z)
  146.  
  147. def _maj(x: int, y: int, z: int):
  148.     """As defined in the specification."""
  149.     return (x & y) ^ (x & z) ^ (y & z)
  150.  
  151. def _rotate_right(num: int, shift: int, size: int = 32):
  152.     """Rotate an integer right."""
  153.     return (num >> shift) | (num << size - shift)
  154.  
  155. if __name__ == "__main__":
  156.     print(generate_hash("Hello").hex())
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