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README.md

pyquinejailgolf

challenge

#!/usr/local/bin/python3

import time
from tempfile import TemporaryDirectory

with TemporaryDirectory() as workdir:
    __import__('os').chdir(workdir)
    __import__('os').mkdir('runtime')

    print("Enter a reverse quine. It must print its source code backwards (including any trailing newlines).")
    print("It must be non-empty and contain 0 quotation marks or dunders. All ascii btw. oh and no builtins.")
    print("To prove you wrote it yourself, it must contain the string 'pyquinejailgolf', and be ==343 chars.")
    print("Well...I'm not sure how you're supposed to write a quine without print statements. u can have em.")
    print("~~~~~~~~~~~~~~~~~~~~~~~~~~~ Type <END> to terminate the program input ~~~~~~~~~~~~~~~~~~~~~~~~~~~")

    prog = []
    while (x := input(">>> ")) != "<END>":
        prog.append(x)
    program = "\n".join(i for i in prog)

    assert x == "<END>", "what did you do this time."
    assert all(ord(i) < 128 for i in program), "i don't speak foreign languages."
    assert all(i not in program for i in ['"', "'", '_']), "who uses strings anyway? it's not like quines require strings."
    assert program != "", "scuse me, just cleaning out the garbage."
    assert "pyquinejailgolf" in program, "are you sure you wrote this program yourself?"
    assert len(program) == 343

    import sys
    stdout = sys.stdout
    with open('runtime/trash.txt', 'w+') as sys.stdout:
        goal = time.time_ns() + 5000000000
        try:
            with open('runtime/external_run.py', 'w+') as f:
                f.write(f"""
with open('runtime/output.txt', 'w+') as __import__('sys').stdout:
    {program = }
    safe_builtins = {{}}
    for i in dir(__builtins__):
        if i[0] not in __import__('string').ascii_lowercase:
            safe_builtins[i] = eval(i)
    safe_builtins['print'] = print
    new_builtins = {{'__builtins__':safe_builtins}}
    try:exec(program, new_builtins, new_builtins)
    except:pass""")
            __import__('os').system('timeout 2.5 /usr/local/bin/python3 runtime/external_run.py')
        except:
            pass

    time.sleep(max(0, (goal - time.time_ns())/1e9))
    sys.stdout = stdout
    with open('runtime/output.txt') as f:
        if (c := f.read()[::-1]) == program:
            print("good jorb")
        else:
            exit("bad")

    with open('/app/flag.txt') as f:
        print(f.read())

solution

we have to create a quine that is 343 chars long, has pyquinejailgolf as text somewhere there, and does not use quotes or underscores. there are also some other restrictions

so, checking what we have access to, we can see that __import__ is still available. while we can't access this directly by using __import__, we can just use an import statement since multiple lines are allowed

so, we can get builtins by doing import builtins. here i import it as b to save on chars for some reason

also, we import string.printable to get all of the chars in a string format since we cant use " or '

then, we read the file and reverse it in code, and also we have to put the end param in print as an empty string

v=[27, 30, 23, 29, 18, 22, 14, 76, 14, 33, 29, 14, 27, 23, 10, 21, 88, 27, 30, 23, 75, 25, 34]
import builtins as b
from string import printable as m
print(b.open(m[:0].join(m[q]for q in v)).read()[83:424].replace(m[85]+m[23],m[-4])[::-1],end=m[:0])
# pyquinejailgolf!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
<END>

the above is a working payload i think