TheAlgorithms · cclauss · Oct 23, 2021 · Oct 22, 2021 · Oct 22, 2021 · Oct 22, 2021
diff --git a/hashes/sha256.py b/hashes/sha256.py
@@ -0,0 +1,248 @@
+# Author: M. Yathurshan
+# Black Formatter: True
+
+"""
+Implementation of SHA256 Hash function in a Python class and provides utilities
+to find hash of string or hash of text from a file.
+
+Usage: python sha256.py --string "Hello World!!"
+       python sha256.py --file "hello_world.txt"
+       When run without any arguments,
+       it prints the hash of the string "Hello World!! Welcome to Cryptography"
+
+References:
+https://qvault.io/cryptography/how-sha-2-works-step-by-step-sha-256/
+https://en.wikipedia.org/wiki/SHA-2
+"""
+
+import argparse
+import struct
+import unittest
+
+
+class SHA256:
+    """
+    Class to contain the entire pipeline for SHA1 Hashing Algorithm
+
+    >>> SHA256(b'Python').hash
+    '18885f27b5af9012df19e496460f9294d5ab76128824c6f993787004f6d9a7db'
+
+    >>> SHA256(b'hello world').hash
+    'b94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9'
+    """
+
+    def __init__(self, data: bytes) -> None:
+        self.data = data
+
+        # Initialize hash values
+        self.hashes = [
+            0x6A09E667,
+            0xBB67AE85,
+            0x3C6EF372,
+            0xA54FF53A,
+            0x510E527F,
+            0x9B05688C,
+            0x1F83D9AB,
+            0x5BE0CD19,
+        ]
+
+        # Initialize round constants
+        self.round_constants = [
+            0x428A2F98,
+            0x71374491,
+            0xB5C0FBCF,
+            0xE9B5DBA5,
+            0x3956C25B,
+            0x59F111F1,
+            0x923F82A4,
+            0xAB1C5ED5,
+            0xD807AA98,
+            0x12835B01,
+            0x243185BE,
+            0x550C7DC3,
+            0x72BE5D74,
+            0x80DEB1FE,
+            0x9BDC06A7,
+            0xC19BF174,
+            0xE49B69C1,
+            0xEFBE4786,
+            0x0FC19DC6,
+            0x240CA1CC,
+            0x2DE92C6F,
+            0x4A7484AA,
+            0x5CB0A9DC,
+            0x76F988DA,
+            0x983E5152,
+            0xA831C66D,
+            0xB00327C8,
+            0xBF597FC7,
+            0xC6E00BF3,
+            0xD5A79147,
+            0x06CA6351,
+            0x14292967,
+            0x27B70A85,
+            0x2E1B2138,
+            0x4D2C6DFC,
+            0x53380D13,
+            0x650A7354,
+            0x766A0ABB,
+            0x81C2C92E,
+            0x92722C85,
+            0xA2BFE8A1,
+            0xA81A664B,
+            0xC24B8B70,
+            0xC76C51A3,
+            0xD192E819,
+            0xD6990624,
+            0xF40E3585,
+            0x106AA070,
+            0x19A4C116,
+            0x1E376C08,
+            0x2748774C,
+            0x34B0BCB5,
+            0x391C0CB3,
+            0x4ED8AA4A,
+            0x5B9CCA4F,
+            0x682E6FF3,
+            0x748F82EE,
+            0x78A5636F,
+            0x84C87814,
+            0x8CC70208,
+            0x90BEFFFA,
+            0xA4506CEB,
+            0xBEF9A3F7,
+            0xC67178F2,
+        ]
+
+        self.preprocessed_data = self.preprocessing(self.data)
+        self.final_hash()
+
+    @staticmethod
+    def preprocessing(data: bytes) -> bytes:
+        padding = b"\x80" + (b"\x00" * (63 - (len(data) + 8) % 64))
+        big_endian_integer = struct.pack(">Q", (len(data) * 8))
+        return data + padding + big_endian_integer
+
+    def final_hash(self) -> None:
+        # Convert into blocks of 64 bytes
+        self.blocks = [
+            self.preprocessed_data[x : x + 64]
+            for x in range(0, len(self.preprocessed_data), 64)
+        ]
+
+        for block in self.blocks:
+            # Convert the given block into a list of 4 byte integers
+            words = list(struct.unpack(">16L", block))
+            # add 48 0-ed integers
+            words += [0] * 48
+
+            a, b, c, d, e, f, g, h = self.hashes
+
+            for index in range(0, 64):
+                if index > 15:
+                    # modify the zero-ed indexes at the end of the array
+                    s0 = (
+                        self.ror(words[index - 15], 7)
+                        ^ self.ror(words[index - 15], 18)
+                        ^ (words[index - 15] >> 3)
+                    )
+                    s1 = (
+                        self.ror(words[index - 2], 17)
+                        ^ self.ror(words[index - 2], 19)
+                        ^ (words[index - 2] >> 10)
+                    )
+
+                    words[index] = (
+                        words[index - 16] + s0 + words[index - 7] + s1
+                    ) % 0x100000000
+
+                # Compression
+                S1 = self.ror(e, 6) ^ self.ror(e, 11) ^ self.ror(e, 25)
+                ch = (e & f) ^ ((~e & (0xFFFFFFFF)) & g)
+                temp1 = (
+                    h + S1 + ch + self.round_constants[index] + words[index]
+                ) % 0x100000000
+                S0 = self.ror(a, 2) ^ self.ror(a, 13) ^ self.ror(a, 22)
+                maj = (a & b) ^ (a & c) ^ (b & c)
+                temp2 = (S0 + maj) % 0x100000000
+
+                h, g, f, e, d, c, b, a = (
+                    g,
+                    f,
+                    e,
+                    ((d + temp1) % 0x100000000),
+                    c,
+                    b,
+                    a,
+                    ((temp1 + temp2) % 0x100000000),
+                )
+
+            mutated_hash_values = [a, b, c, d, e, f, g, h]
+
+            # Modify final values
+            self.hashes = [
+                ((element + mutated_hash_values[index]) % 0x100000000)
+                for index, element in enumerate(self.hashes)
+            ]
+
+        self.hash = "".join([hex(value)[2:].zfill(8) for value in self.hashes])
+
+    def ror(self, value: int, rotations: int) -> int:
+        """
+        Right rotate a given unsigned number by a certain amount of rotations
+        """
+        return 0xFFFFFFFF & (value << (32 - rotations)) | (value >> rotations)
+
+
+class SHA256HashTest(unittest.TestCase):
+    """
+    Test class for the SHA256 class. Inherits the TestCase class from unittest
+    """
+
+    def test_match_hashes(self) -> None:
+        import hashlib
+
+        msg = bytes("Test String", "utf-8")
+        self.assertEqual(SHA256(msg).hash, hashlib.sha256(msg).hexdigest())
+
+
+def main() -> None:
+    """
+    Provides option 'string' or 'file' to take input
+    and prints the calculated SHA-256 hash
+    """
+
+    # unittest.main()
+
+    import doctest
+
+    doctest.testmod()
+
+    parser = argparse.ArgumentParser()
+    parser.add_argument(
+        "-s",
+        "--string",
+        dest="input_string",
+        default="Hello World!! Welcome to Cryptography",
+        help="Hash the string",
+    )
+    parser.add_argument(
+        "-f", "--file", dest="input_file", help="Hash contents of a file"
+    )
+
+    args = parser.parse_args()
+
+    input_string = args.input_string
+
+    # hash input should be a bytestring
+    if args.input_file:
+        with open(args.input_file, "rb") as f:
+            hash_input = f.read()
+    else:
+        hash_input = bytes(input_string, "utf-8")
+
+    print(SHA256(hash_input).hash)
+
+
+if __name__ == "__main__":
+    main()