Implementation of SHA-256 using Python

hashes/sha256.py

@@ -0,0 +1,169 @@
+# 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/ --> in detail
+https://en.wikipedia.org/wiki/SHA-2 --> Pseudocode
+"""
+
+import argparse
+import struct
+
+
+class SHA256:
+    """
+    Class to contain the entire pipeline for SHA1 Hashing Algorithm
+
+    >>> SHA256(bytes('Python', 'utf-8')).hash
+    '18885f27b5af9012df19e496460f9294d5ab76128824c6f993787004f6d9a7db'
+
+    >>> SHA256(bytes('hello world', 'utf-8')).hash
+    'b94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9'
+    """
+
+    def __init__(self, data: bytes):
+        self.data = data
+
+        # fmt: off
+
+        # Initialize hash values
+        self.h = [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
+        ]
+
+        # fmt: on
+
+        self.preprocessing()
+        self.final_hash()
+
+    def preprocessing(self):
+        padding = b"\x80" + (b"\x00" * (63 - (len(self.data) + 8) % 64))
+        big_endian_integer = struct.pack(">Q", (len(self.data) * 8))
+        self.preprocessed_data = self.data + padding + big_endian_integer
+
+    def final_hash(self):
+        # 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.h
+
+            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.h = [
+                ((element + mutated_hash_values[index]) % 0x100000000)
+                for index, element in enumerate(self.h)
+            ]
+
+        self.hash = "".join([hex(value)[2:].zfill(8) for value in self.h])
+
+    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)
+
+
+def main():
+    """
+    Provides option 'string' or 'file' to take input
+    and prints the calculated SHA-256 hash
+    """
+    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()
+
+    import doctest
+
+    doctest.testmod()