Python script to calculate minimum length of a key to achieve a given level of security.

calculate_strength.py

#
# Calculate required key/password length to achieve satisfactory level
# of security. E.g. if you want something to be pretty secure so it can
# handle a week of brute forcing by pretty big hash farms.
#
# License: WTFPL http://www.wtfpl.net/
#

# How long do you want the cracking to take
TARGET_DURATION = 60 * 60 * 24 * 3  # Seconds

UPPER = 26  # Uppercase characters in the English alphabet
LOWER = 26  # Lowercase characters in the English alphabet
DIGITS = 10  # Digits 0-9
SYMBOLS = len("!@#$%&/(){}[]=+-,.")  # What symbols you want to use

SEARCH_SPACE_DEPTH = UPPER + LOWER + DIGITS + SYMBOLS
GUESSES_PER_SECOND = 100000000000  # 100 billion


def space_duration(length, depth, persec):
    space = depth ** length
    duration = space / persec

    return space, duration


def seconds_to_readable(seconds):
    minutes, seconds = divmod(seconds, 60)
    hours, minutes = divmod(minutes, 60)
    days, hours = divmod(hours, 24)

    return "{}d {}h {}m {}s".format(days, hours, minutes, seconds)


if __name__ == "__main__":
    print("Your search space depth is {} characters".format(
        SEARCH_SPACE_DEPTH
    ))
    print("You assume {:,} guesses per second".format(GUESSES_PER_SECOND))

    characters = 0
    space, duration = 0, 0
    while duration < TARGET_DURATION:
        characters += 1
        space, duration = space_duration(characters, SEARCH_SPACE_DEPTH,
                                         GUESSES_PER_SECOND)

    print("Your target length is >= {} characters".format(
        characters
    ))

    print(
        "You will achieve {:,} search space size, and it will take {} to bruteforce".format(
            space,
            seconds_to_readable(duration)
        ))