md5.py

import math


def rearrange(bitString32):
    """[summary]
    Regroups the given binary string.

    Arguments:
        bitString32 {[string]} -- [32 bit binary]

    Raises:
    ValueError -- [if the given string not are 32 bit binary string]

    Returns:
        [string] -- [32 bit binary string]
    >>> rearrange('1234567890abcdfghijklmnopqrstuvw')
    'pqrstuvwhijklmno90abcdfg12345678'
    """

    if len(bitString32) != 32:
        raise ValueError("Need length 32")
    newString = ""
    for i in [3, 2, 1, 0]:
        newString += bitString32[8 * i : 8 * i + 8]
    return newString


def reformatHex(i):
    """[summary]
    Converts the given integer into 8-digit hex number.

    Arguments:
            i {[int]} -- [integer]
    >>> reformatHex(666)
    '9a020000'
    """

    hexrep = format(i, "08x")
    thing = ""
    for i in [3, 2, 1, 0]:
        thing += hexrep[2 * i : 2 * i + 2]
    return thing


def pad(bitString):
    """[summary]
    Fills up the binary string to a 512 bit binary string

    Arguments:
            bitString {[string]} -- [binary string]

    Returns:
            [string] -- [binary string]
    """
    startLength = len(bitString)
    bitString += "1"
    while len(bitString) % 512 != 448:
        bitString += "0"
    lastPart = format(startLength, "064b")
    bitString += rearrange(lastPart[32:]) + rearrange(lastPart[:32])
    return bitString


def getBlock(bitString):
    """[summary]
    Iterator:
            Returns by each call a list of length 16 with the 32 bit
            integer blocks.

    Arguments:
            bitString {[string]} -- [binary string >= 512]
    """

    currPos = 0
    while currPos < len(bitString):
        currPart = bitString[currPos : currPos + 512]
        mySplits = []
        for i in range(16):
            mySplits.append(int(rearrange(currPart[32 * i : 32 * i + 32]), 2))
        yield mySplits
        currPos += 512


def not32(i):
    """
    >>> not32(34)
    4294967261
    """
    i_str = format(i, "032b")
    new_str = ""
    for c in i_str:
        new_str += "1" if c == "0" else "0"
    return int(new_str, 2)


def sum32(a, b):
    return (a + b) % 2**32


def leftrot32(i, s):
    return (i << s) ^ (i >> (32 - s))


def md5me(testString):
    """[summary]
    Returns a 32-bit hash code of the string 'testString'

    Arguments:
            testString {[string]} -- [message]
    """

    bs = ""
    for i in testString:
        bs += format(ord(i), "08b")
    bs = pad(bs)

    tvals = [int(2**32 * abs(math.sin(i + 1))) for i in range(64)]

    a0 = 0x67452301
    b0 = 0xEFCDAB89
    c0 = 0x98BADCFE
    d0 = 0x10325476

    s = [
        7,
        12,
        17,
        22,
        7,
        12,
        17,
        22,
        7,
        12,
        17,
        22,
        7,
        12,
        17,
        22,
        5,
        9,
        14,
        20,
        5,
        9,
        14,
        20,
        5,
        9,
        14,
        20,
        5,
        9,
        14,
        20,
        4,
        11,
        16,
        23,
        4,
        11,
        16,
        23,
        4,
        11,
        16,
        23,
        4,
        11,
        16,
        23,
        6,
        10,
        15,
        21,
        6,
        10,
        15,
        21,
        6,
        10,
        15,
        21,
        6,
        10,
        15,
        21,
    ]

    for m in getBlock(bs):
        A = a0
        B = b0
        C = c0
        D = d0
        for i in range(64):
            if i <= 15:
                # f = (B & C) | (not32(B) & D)
                f = D ^ (B & (C ^ D))
                g = i
            elif i <= 31:
                # f = (D & B) | (not32(D) & C)
                f = C ^ (D & (B ^ C))
                g = (5 * i + 1) % 16
            elif i <= 47:
                f = B ^ C ^ D
                g = (3 * i + 5) % 16
            else:
                f = C ^ (B | not32(D))
                g = (7 * i) % 16
            dtemp = D
            D = C
            C = B
            B = sum32(B, leftrot32((A + f + tvals[i] + m[g]) % 2**32, s[i]))
            A = dtemp
        a0 = sum32(a0, A)
        b0 = sum32(b0, B)
        c0 = sum32(c0, C)
        d0 = sum32(d0, D)

    digest = reformatHex(a0) + reformatHex(b0) + reformatHex(c0) + reformatHex(d0)
    return digest


def test():
    assert md5me("") == "d41d8cd98f00b204e9800998ecf8427e"
    assert (
        md5me("The quick brown fox jumps over the lazy dog")
        == "9e107d9d372bb6826bd81d3542a419d6"
    )
    print("Success.")


if __name__ == "__main__":
    test()
    import doctest

    doctest.testmod()