Class SHA1Hash

sha1.py:7–97

Class to contain the entire pipeline for SHA1 Hashing Algorithm

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.
        """