SHA-1 implementation produced by ChatGPT

sha1.py

import struct

def sha1(data):
    """
    Implementation of the SHA-1 hash function in pure Python.
    """
    # Initialize variables
    h0 = 0x67452301
    h1 = 0xEFCDAB89
    h2 = 0x98BADCFE
    h3 = 0x10325476
    h4 = 0xC3D2E1F0

    # Pre-processing
    original_byte_len = len(data)
    original_bit_len = original_byte_len * 8
    data += b'\x80'
    data += b'\x00' * ((56 - (original_byte_len + 1) % 64) % 64)
    data += struct.pack('>Q', original_bit_len)

    # Process the message in successive 512-bit chunks
    for i in range(0, len(data), 64):
        w = [0] * 80
        for j in range(16):
            w[j] = struct.unpack('>I', data[i + j*4:i + j*4 + 4])[0]
        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

        # Main loop
        for i in range(80):
            if 0 <= i <= 19:
                f = (b & c) | (~b & 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)

        # Add 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)

def left_rotate(n, b):
    """
    Left rotate a 32-bit unsigned integer n by b bits.
    """
    return ((n << b) | (n >> (32 - b))) & 0xffffffff

test.py

from sha1 import sha1

import hashlib


TEST_VECTOR = b'', b'test', b'aaaaaaabaaacaaadaaaeaaafaaag'
for t in TEST_VECTOR:
    assert sha1(b"test") == hashlib.sha1(b"test").hexdigest()