sha1.py

#!/usr/bin/env python

from __future__ import print_function, unicode_literals
import struct

try:
    range = xrange
except NameError:
    pass

def _left_rotate(n, b):
    return ((n << b) | (n >> (32 - b))) & 0xffffffff
    
def sha1(message):
    """SHA-1 Hashing Function

    A custom SHA-1 hashing function implemented entirely in Python.

    Arguments:
        message: The input message string to hash.

    Returns:
        A hex SHA-1 digest of the input message.
    """
    # Initialize variables:
    h0 = 0x67452301
    h1 = 0xEFCDAB89
    h2 = 0x98BADCFE
    h3 = 0x10325476
    h4 = 0xC3D2E1F0
    
    # Pre-processing:
    original_byte_len = len(message)
    original_bit_len = original_byte_len * 8
    # append the bit '1' to the message
    message += b'\x80'
    
    # append 0 <= k < 512 bits '0', so that the resulting message length (in bits)
    #    is congruent to 448 (mod 512)
    message += b'\x00' * ((56 - (original_byte_len + 1) % 64) % 64)
    
    # append length of message (before pre-processing), in bits, as 64-bit big-endian integer
    message += struct.pack(b'>Q', original_bit_len)
    # Process the message in successive 512-bit chunks:
    # break message into 512-bit chunks
    for i in range(0, len(message), 64):
        w = [0] * 80
        # break chunk into sixteen 32-bit big-endian words w[i]
        for j in range(16):
            w[j] = struct.unpack(b'>I', message[i + j*4:i + j*4 + 4])[0]
        # Extend the sixteen 32-bit words into eighty 32-bit words:
        for j in range(16, 80):
            w[j] = _left_rotate(w[j-3] ^ w[j-8] ^ w[j-14] ^ w[j-16], 1)
    
        # Initialize hash value for this chunk:
        a = h0
        b = h1
        c = h2
        d = h3
        e = h4
    
        for i in range(80):
            if 0 <= i <= 19:
                # Use alternative 1 for f from FIPS PB 180-1 to avoid ~
                f = d ^ (b & (c ^ d))
                k = 0x5A827999
            elif 20 <= i <= 39:
                f = b ^ c ^ d
                k = 0x6ED9EBA1
            elif 40 <= i <= 59:
                f = (b & c) | (b & d) | (c & d) 
                k = 0x8F1BBCDC
            elif 60 <= i <= 79:
                f = b ^ c ^ d
                k = 0xCA62C1D6
    
            a, b, c, d, e = ((_left_rotate(a, 5) + f + e + k + w[i]) & 0xffffffff, 
                            a, _left_rotate(b, 30), c, d)
    
        # sAdd this chunk's hash to result so far:
        h0 = (h0 + a) & 0xffffffff
        h1 = (h1 + b) & 0xffffffff 
        h2 = (h2 + c) & 0xffffffff
        h3 = (h3 + d) & 0xffffffff
        h4 = (h4 + e) & 0xffffffff
    
    # Produce the final hash value (big-endian):
    return '%08x%08x%08x%08x%08x' % (h0, h1, h2, h3, h4)
    
if __name__ == '__main__':
    # Imports required for command line parsing. No need for these elsewhere
    import argparse
    import sys 
    import os

    # Parse the incoming arguments
    parser = argparse.ArgumentParser()
    parser.add_argument('input', nargs='?',
             help='input file or message to hash')
    args = parser.parse_args()

    data = None

    if args.input is None:
        # No argument given, assume message comes from standard input
        try:
            # sys.stdin is opened in text mode, which can change line endings,
            # leading to incorrect results. Detach fixes this issue, but it's
            # new in Python 3.1
            data = sys.stdin.detach().read()
        except AttributeError:
            # Linux ans OSX both use \n line endings, so only windows is a
            # problem.
            if sys.platform == "win32": 
                import msvcrt
                msvcrt.setmode(sys.stdin.fileno(), os.O_BINARY) 
            data = sys.stdin.read().encode()
    elif os.path.isfile(args.input):
        # An argument is given and it's a valid file. Read it
        with open(args.input, 'rb') as f:
            data = f.read()
    else:
        data = args.input
    
    # Show the final digest
    print('sha1-digest:', sha1(data))