diff --git a/hashes/sha1.py b/hashes/sha1.py new file mode 100644 index 000000000..e34f87a76 --- /dev/null +++ b/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()