Bruteforce Apple Disk Image (DMG) from command line (CLI)

This was used because I wrongly typed part of my password for an old dmg image, so it was a success for my needs.

import subprocess
import sys

password = 'PASS'
file = 'docs.dmg'
charset = 'abc'

def gen_pass(line):
    base = len(charset)
    result = 0
    exponent = 0
    genstr = ""
    while result < line:
        exponent += 1
        result += base ** exponent
    result -= base ** exponent
    for e in range(exponent - 1, -1, -1):
        pos = -1
        while result < line:
            result += base ** e
            pos += 1
        result -= base ** e
        genstr += charset[pos]
    return genstr

def check_password(file, password, line):
    local_password = '{0}{1}'.format(password, gen_pass(line))
    print(line, local_password)
    proc, err = subprocess.Popen(
        ['hdiutil', 'verify', '-stdinpass', file],
        bufsize=-1,
        stdin=subprocess.PIPE,
        stderr=subprocess.PIPE
    ).communicate(input=local_password)
    if 'Authentication error' in err:
        check_password(file, password, line+1)
    else:
        print('Password Found: {0}'.format(local_password))

check_password(file, password, 1)