Prompt

We have created a python script for you to break into as training. See if you can figure out a password that will authenticate with the program.

PYTHON3.pyc0.6KB

Walk-Through

This challenge involves analyzing vulnerabilities in a compiled Python program. The uncompyle program can be used to convert the compiled program back into Python code. See Python2 for more information on decompiling this file.

The result of running uncompyle can be seen below:

import sys

def main():
    if len(sys.argv) != 2:
        print 'Invalid args'
        return
    password = sys.argv[1]
    builder = 0
    for c in password:
        builder += ord(c)

    builder = builder << 2
    builder = ~builder
    builder = builder ^ 12648430
    builder = ~builder
    if builder == 12645638 and ord(password[0]) == 78 and len(password) == 11:
        print 'correct'
    else:
        print 'incorrect'


if __name__ == '__main__':
    main()

Guide

This challenge presents some elements similar to Python1. However, there are some new functions performed to builder.

An analysis of the code reveals that the sum of the ASCII codes for the characters in the password list will have a specific value after several transformations.

‣

Open this toggle to learn more about the specific transformations:

Below is an example of code in Python that can reverse the transformations to get the total for builder before it is transformed. This can be run in its own program, or referenced to calculate the answer by hand. This process will help determine the total Unicode value of the characters entered.

The code will subtract the value of the first character (’N’=78) to get the sum of the next ten remaining characters. Dividing that sum by 10 will yield the Unicode for a character repeated ten times.

target = 12645638
temp = ~target
temp = temp ^ 12648430
temp = ~temp
totalUnicode = temp // 4
totalUnicode = totalUnicode-78
print("Total for 10 remaining characters: ", totalUnicode)
x = totalUnicode // 10
print("x value:", x)
print("There are 10 characters like this: ", chr(x))

The last line will print the character that can be repeated ten times in the input, however, other combinations of characters after ‘N’ are accepted as long as the conditions are met.

Questions

1. What is an input to this program that will result in a correct validation?

Reverse the transformations made in the program to determine the input.

Python 3

Prompt

Walk-Through

Guide

Questions

1. What is an input to this program that will result in a correct validation?