SHA1 class completed, Test passed

hashes/sha1.py

@@ -1,16 +1,22 @@
 """
 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 Welcome to Cryptography"
+Usage: python sha1.py --string "Hello World!!"
        pyhton sha1.py --file "hello_world.txt"
-       Without any arguments prints the hash of the string "Hello World"
+       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. The blocks are then
-processed one at a time. Each block must be expanded and compressed.
+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.
@@ -18,79 +24,123 @@ 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
     """
-    
-    H0 - 01100111010001010010001100000001
-    H1 - 11101111110011011010101110001001
-    H2 - 10011000101110101101110011111110
-    H3 - 00010000001100100101010001110110
-    H4 - 11000011110100101110000111110000
 
     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.current_hash = ''
+        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):
-        return
+        """
+        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_block(self):
-        return
+    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)]
 
-    def expand_block(self):
-        return
-
-    def compress_block(self):
-        return
+    # @staticmethod
+    def expand_block(self, block):
+        """
+        Takes block of 64 and returns list of length 80.
+        It is really a static method but
+        we need the rotate method inside, so we will have to use self
+        """
+        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):
-        return 'This is in my To Do list'
+        """
+        Calls all the other methods to process the input. Returns SHA1 hash
+        """
+        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
 
-class SHA1HashTest:
+        return '%08x%08x%08x%08x%08x' %tuple(self.h)
+
+
+class SHA1HashTest(unittest.TestCase):
     """
-    Test class for the SHA1 class
+    Test class for the SHA1Hash class. Inherits the TestCase class from unittest
     """
-    def __init__(self, data):
-        self.data = data
+    def testMatchHashes(self):
+        msg = bytes("Hello World", 'utf-8')
+        self.assertEqual(SHA1Hash(msg).final_hash(), hashlib.sha1(msg).hexdigest())
 
-    def calculated_hash(self):
-        return SHA1Hash(self.data).final_hash()
-
-    def hashlib_hash(self):
-        return hashlib.sha1(self.data.byte_encode()).hexdigest()
-
-    def byte_encode(self):
-        return bytes(self.data, 'utf-8')
-
-    def match_hashes(self):
-        # self.assertEqual(self.calculated_hash(), self.hashlib_hash())
-        return self.calculated_hash() == self.hashlib_hash()
-
-def run_test_case(hash_input = 'Hello World'):
+def run_test():
     """
-    Pulled this out of main because we probably dont want to run the Test
-    each time we want to calculate hash.
+    Run the unit test. Pulled this out of main because we probably dont want to run
+    the test each time.
     """
-    print(SHA1HashTest(hash_input).match_hashes())
-
+    unittest.main()
 
 def main():
+    """
+    Provides option string or file to take input and prints the calculated SHA1 hash
+    """
     parser = argparse.ArgumentParser(description='Process some strings or files')
-    parser.add_argument('--string', dest='input_string', default='Hello World',
+    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, 'r').read()
+        hash_input = open(args.input_file, 'rb').read()
     else:
-        hash_input = input_string
+        hash_input = bytes(input_string, 'utf-8')
     print(SHA1Hash(hash_input).final_hash())
 
 if __name__ == '__main__':