Merge pull request #347 from piyush-kgp/Hashes

Added SHA1 algorithm in hashes folder

hashes/sha1.py

@@ -0,0 +1,147 @@
+"""
+Demonstrates implementation of SHA1 Hash function in a Python class and gives utilities
+to find hash of string or hash of text from a file.
+Usage: python sha1.py --string "Hello World!!"
+       pyhton sha1.py --file "hello_world.txt"
+       When run without any arguments, it prints the hash of the string "Hello World!! Welcome to Cryptography"
+Also contains a Test class to verify that the generated Hash is same as that
+returned by the hashlib library
+
+SHA1 hash or SHA1 sum of a string is a crytpographic function which means it is easy
+to calculate forwards but extemely difficult to calculate backwards. What this means
+is, you can easily calculate the hash of  a string, but it is extremely difficult to
+know the original string if you have its hash. This property is useful to communicate
+securely, send encrypted messages and is very useful in payment systems, blockchain
+and cryptocurrency etc.
+The Algorithm as described in the reference:
+First we start with a message. The message is padded and the length of the message
+is added to the end. It is then split into blocks of 512 bits or 64 bytes. The blocks
+are then processed one at a time. Each block must be expanded and compressed.
+The value after each compression is added to a 160bit buffer called the current hash
+state. After the last block is processed the current hash state is returned as
+the final hash.
+Reference: https://deadhacker.com/2006/02/21/sha-1-illustrated/
+"""
+
+import argparse
+import struct
+import hashlib #hashlib is only used inside the Test class
+import unittest
+
+
+class SHA1Hash:
+    """
+    Class to contain the entire pipeline for SHA1 Hashing Algorithm
+    """
+    def __init__(self, data):
+        """
+        Inititates the variables data and h. h is a list of 5 8-digit Hexadecimal
+        numbers corresponding to (1732584193, 4023233417, 2562383102, 271733878, 3285377520)
+        respectively. We will start with this as a message digest. 0x is how you write
+        Hexadecimal numbers in Python
+        """
+        self.data = data
+        self.h = [0x67452301, 0xEFCDAB89, 0x98BADCFE, 0x10325476, 0xC3D2E1F0]
+
+    @staticmethod
+    def rotate(n, b):
+        """
+        Static method to be used inside other methods. Left rotates n by b.
+        """
+        return ((n << b) | (n >> (32 - b))) & 0xffffffff
+
+    def padding(self):
+        """
+        Pads the input message with zeros so that padded_data has 64 bytes or 512 bits
+        """
+        padding = b'\x80' + b'\x00'*(63 - (len(self.data) + 8) % 64)
+        padded_data = self.data + padding + struct.pack('>Q', 8 * len(self.data))
+        return padded_data
+
+    def split_blocks(self):
+        """
+        Returns a list of bytestrings each of length 64
+        """
+        return [self.padded_data[i:i+64] for i in range(0, len(self.padded_data), 64)]
+
+    # @staticmethod
+    def expand_block(self, block):
+        """
+        Takes a bytestring-block of length 64, unpacks it to a list of integers and returns a
+        list of 80 integers pafter some bit operations
+        """
+        w = list(struct.unpack('>16L', block)) + [0] * 64
+        for i in range(16, 80):
+            w[i] = self.rotate((w[i-3] ^ w[i-8] ^ w[i-14] ^ w[i-16]), 1)
+        return w
+
+    def final_hash(self):
+        """
+        Calls all the other methods to process the input. Pads the data, then splits into
+        blocks and then does a series of operations for each block (including expansion).
+        For each block, the variable h that was initialized is copied to a,b,c,d,e
+        and these 5 variables a,b,c,d,e undergo several changes. After all the blocks are
+        processed, these 5 variables are pairwise added to h ie a to h[0], b to h[1] and so on.
+        This h becomes our final hash which is returned.
+        """
+        self.padded_data = self.padding()
+        self.blocks = self.split_blocks()
+        for block in self.blocks:
+            expanded_block = self.expand_block(block)
+            a, b, c, d, e = self.h
+            for i in range(0, 80):
+                if 0 <= i < 20:
+                    f = (b & c) | ((~b) & d)
+                    k = 0x5A827999
+                elif 20 <= i < 40:
+                    f = b ^ c ^ d
+                    k = 0x6ED9EBA1
+                elif 40 <= i < 60:
+                    f = (b & c) | (b & d) | (c & d)
+                    k = 0x8F1BBCDC
+                elif 60 <= i < 80:
+                    f = b ^ c ^ d
+                    k = 0xCA62C1D6
+                a, b, c, d, e = self.rotate(a, 5) + f + e + k + expanded_block[i] & 0xffffffff,\
+                                a, self.rotate(b, 30), c, d
+        self.h = self.h[0] + a & 0xffffffff,\
+                 self.h[1] + b & 0xffffffff,\
+                 self.h[2] + c & 0xffffffff,\
+                 self.h[3] + d & 0xffffffff,\
+                 self.h[4] + e & 0xffffffff
+        return '%08x%08x%08x%08x%08x' %tuple(self.h)
+
+
+class SHA1HashTest(unittest.TestCase):
+    """
+    Test class for the SHA1Hash class. Inherits the TestCase class from unittest
+    """
+    def testMatchHashes(self):
+        msg = bytes('Test String', 'utf-8')
+        self.assertEqual(SHA1Hash(msg).final_hash(), hashlib.sha1(msg).hexdigest())
+
+
+def main():
+    """
+    Provides option 'string' or 'file' to take input and prints the calculated SHA1 hash.
+    unittest.main() has been commented because we probably dont want to run
+    the test each time.
+    """
+    # unittest.main()
+    parser = argparse.ArgumentParser(description='Process some strings or files')
+    parser.add_argument('--string', dest='input_string',
+                        default='Hello World!! Welcome to Cryptography',
+                        help='Hash the string')
+    parser.add_argument('--file', dest='input_file', help='Hash contents of a file')
+    args = parser.parse_args()
+    input_string = args.input_string
+    #In any case hash input should be a bytestring
+    if args.input_file:
+        hash_input = open(args.input_file, 'rb').read()
+    else:
+        hash_input = bytes(input_string, 'utf-8')
+    print(SHA1Hash(hash_input).final_hash())
+
+
+if __name__ == '__main__':
+    main()