Barbara Liskov

Barbara Liskov

Barbara Liskov (born November 7, 1939 as Barbara Jane Huberman) is an American computer scientist who has made pioneering contributions to programming languages and distributed computing. Her notable work includes the development of the Liskov substitution principle which describes the fundamental nature of data abstraction, and is used in type theory (see subtyping) and in object-oriented programming (see inheritance). Her work was recognized with the 2008 Turing Award, the highest distinction in computer science. - Wikipedia Entry

Description

Chal: Return the flag back to the 2008 Turing Award Winner

Author: Josh

BarbaraLiskov.pyc

Solution

We are given a pyc file, which is python compiled bytecode.

Naive

Naive solution would be to use strings and figure out the contents.

└─$ strings BarbaraLiskov.pyc 
...
validate_inputr
Nz`Y2hjdGZ7dV9uM3Yzcl9uMzNkXzBwdDFtNGxfcDNyZjBybTRuYzMsX3VfbjMzZF9nMDBkLTNuMHVnaF9wM3JmMHJtNG5jM30=r
base64
...

Take what seems to be the Base64 blob -> Y2hjdGZ7dV9uM3Yzcl9uMzNkXzBwdDFtNGxfcDNyZjBybTRuYzMsX3VfbjMzZF9nMDBkLTNuMHVnaF9wM3JmMHJtNG5jM30=

Decode: chctf{u_n3v3r_n33d_0pt1m4l_p3rf0rm4nc3,_u_n33d_g00d-3n0ugh_p3rf0rm4nc3}

Proper

Use Decompyle++ (pycdc) to recover original python code.

└─$ pycdc ./BarbaraLiskov.pyc 
# Source Generated with Decompyle++
# File: BarbaraLiskov.pyc (Python 3.11)

import base64

def secret_code():
    obfuscated_string = '492d576f6e2d412d547572696e672d4177617264'
    return bytes.fromhex(obfuscated_string).decode('utf-8')


def validate_input(user_input):
    return user_input == secret_code()


def print_the_flag():
    encoded_string = 'Y2hjdGZ7dV9uM3Yzcl9uMzNkXzBwdDFtNGxfcDNyZjBybTRuYzMsX3VfbjMzZF9nMDBkLTNuMHVnaF9wM3JmMHJtNG5jM30='
    bytes = base64.b64decode(encoded_string)
    data = bytes.decode('utf-8')
    print(data)


def main():
    user_input = input('Enter the digital code >>> ')
    if validate_input(user_input):
        print_the_flag()
        return None
    None('<<< Incorrect code.')

if __name__ == '__main__':
    main()
    return None

➜ py
Python 3.9.5 (tags/v3.9.5:0a7dcbd, May  3 2021, 17:27:52) [MSC v.1928 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import base64
>>> def print_the_flag():
...     encoded_string = 'Y2hjdGZ7dV9uM3Yzcl9uMzNkXzBwdDFtNGxfcDNyZjBybTRuYzMsX3VfbjMzZF9nMDBkLTNuMHVnaF9wM3JmMHJtNG5jM30='
...     bytes = base64.b64decode(encoded_string)
...     data = bytes.decode('utf-8')
...     print(data)
...
>>> print_the_flag()
chctf{u_n3v3r_n33d_0pt1m4l_p3rf0rm4nc3,_u_n33d_g00d-3n0ugh_p3rf0rm4nc3}

Flag: chctf{u_n3v3r_n33d_0pt1m4l_p3rf0rm4nc3,_u_n33d_g00d-3n0ugh_p3rf0rm4nc3}