Almost Illegal Strings, Mark II (Cops)

Question

Edit 2020-11-06: This challenge has been edited with new provisions to encourage participation. The edits have been bolded for emphasis.

Welcome to a cops and robbers version of Find an Illegal String.

An illegal string is "a string of characters that cannot appear in any legal program in your programming language of choice" (from the linked post).

For this challenge, we will define an almost illegal string, which is a string of characters that is very hard, but not impossible, to include in a valid program.

The Cops' Challenge

• Choose a programming language, and choose an 'almost illegal string' - this is a sequence of characters that is very hard to include in a valid program without causing it to error.
• Write a program that contains the 'almost illegal string' as a contiguous substring that does not error.
• Optionally, you may also specify a set of banned characters. These are characters that do not appear in your program, except in the 'almost illegal string'. (Therefore: banned characters can still appear inside the almost illegal string)

That's it! You will reveal the programming language, the almost illegal string, and the set of banned characters, and challenge robbers to write a program that contains the illegal string but does not error.

For the purposes of this challenge, we define 'does not error' as:

• Your program exits with exit code 0.
• Your program does not print any output to standard error.
• Your program may print anything to standard output, if you wish, but it does not have to.
• If (and only if) your language always prints output to standard error regardless of the program, such as debugging or timing information, you may instead design a program that only outputs this to standard error. If you are making use of this clause, mention it in your cop post.

The Robbers' Challenge

Find an uncracked answer. Write a program in the language specified that contains as a contiguous substring the almost illegal string specified and does not error. Your program may not use any character in the set of banned characters, unless it is part of the almost illegal string. Your program does not need to be exactly what the cop had in mind. Post an answer to the robber's thread and leave a comment on the cops' answer to crack it.

Clarifications

• If your cop answer requires a specific operating environment or version, you must specify this in your answer.
• The cop's almost illegal string that they reveal is to be interpreted with respect to the standard encoding for the language's interpreter. For most programs, this will be UTF8.
• Solutions should not take any input (via standard input, argv, or any other source) and may assume no such input is given.
• Solutions must terminate in a finite amount of time. This means entering an infinite loop and getting killed by TIO's 60 second timeout is not a valid solution.
• Cops should make sure if their almost illegal string contains leading or trailing newlines that it is very clear it does so. Robbers should carefully note any leading or trailing newlines in a cop's post.

Formatting hint

The clearest way to include leading or trailing newlines is to use the backtick syntax for your post:

```

foo

```

Renders as:

foo

To remove any ambiguity, explicitly mention the leading/trailing newlines in your post.

Scoring

After 10 days without a crack, a cop can mark their answer as safe and reveal their solution. Once the cop has revealed their solution, it is no longer able to be cracked.

Cops are scored based on the length (in bytes) of their almost illegal string in their safe answer(s), with lower being better.

Robbers are scored by the number of answers they crack, with higher being better.

---

Example

Python 3, 5 bytes

Illegal string:

"'1/0

Banned characters:

#'

Python 3, cracks example's answer

Program:

""" "'1/0 """

The idea is that we can just comment out the string, since " is not banned.

Answer 1

Python 2, 5 bytes (cracked by tsh)

bin()

Try it online!

Banned: all characters except alphanumeric characters

abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789

So, you're allowed the above characters and nothing else (in addition to bin() itself).

(This idea isn't mine, I remember it from an earlier challenge, but I don't remember who deserves credit for it.)

Answer 2

Haskell, 3 bytes

#"

(begins with a newline)

Disallowed charachters: -

Answer 3

Jelly, 4 bytes, cracked by HyperNeutrino

«{

Try it online!

You may not use newlines. Any other character/byte is fair game

---

My intended solution was any of the banned characters here aside from ”. Each of these characters cause the parsing of the link to break, meaning everything before them gets ignored:

Try it online!

Answer 4

Python 3, 7 bytes, cracked by @EasyasPi

Still not the intended answer, so I'm just revealing it. Scroll to the bottom to see it.

raise

Banned characters

TAB "'(),.=[\]_{|}

Non-ASCII characters are all banned as well. Try it online or validate it online!

Some cracks that work without the banned chars

'''
raise'''

"""
raise"""

raise SystemExit

raiseTABSystemExit # originally posted by EasyasPi here, he found yet another loophole

raise\
SystemExit

raiser=3 # originally posted by EasyasPi on v1 of this challenge

Intended Answer

#coding:U7
quit+ACgAKQ-
raise

This works because

the magic comment at the top sets the file encoding to UTF-7

and

in UTF-7, characters can be encoded by first converting them to their UTF-16 binary representations, and concatenating them if there are multiple characters to be encoded. Here, we want to call quit, so we need to convert (). This becomes 0000 0000 0010 1000 0000 0000 0010 1001. Next, we regroup them into groups of 6, to get 000000 000010 100000 000000 001010 01, and pad the last group with trailing zeros (if necessary). In this case, we get 000000 000010 100000 000000 001010 010000. Finally, we convert these to the corresponding Base64 characters (table here), getting ACgAKQ, prepend a +, and append a -.

So,

() in UTF-7 is +ACgAKQ-. We use this fact to bypass the banned () and call quit anyways, by replacing () with +ACgAKQ-. This exits the program before it can throw any errors.

Answer 5

Jelly, 4 bytes, cracked by Unrelated String

«{

Try it online!

I'm giving Jelly another go, but with slightly more restrictions. You may not use quƁƘȤ(ƈɦƙɱɲƥʠʂȥ (the unimplemented commands in Jelly), ” or newlines, as these make it far too trivial to crack (thanks to HyperNeutrino for showing that)

---

Neither HyperNeutrino's crack in the comments, nor Unrelated String's crack was my intended solution. Putting a Œ (or any of ÐÆØœæ) with nothing after it at the end causes the same behaviour as any of quƁƘȤ(ƈɦƙɱɲƥʠʂȥ, as they always expect to have a character after them. Without any character, they cause a break in the program chain, meaning that everything before them is ignored:

Try it online!

Answer 6

R, 2 bytes, cracked by Dominic van Essen

'"

Try it online!

Banned characters (newlines are banned):

'"`#\qel
    

This bans the obvious cracks I can think of, but I wouldn't be surprised if you come up with a crack very different to what I intend.

Dominic van Essen cracked a first version of this challenge, and then a second; then Giuseppe cracked a third version. I have added qel and newlines to the list of banned character to sidestep their cracks.

---

The solution I had in mind was

assign(intToUtf8(c(37,39,34,37)), c); 1 %'"% 2

Try it online!

The assign call creates a new binary operator, %'"%; it is equivalent to "%'"%" <- c. In R, you can create new operators of the form %x% where x is any string: %}%, %$@% and %µ£$% are all valid operator names. Here, the new operator is equal to the concatenation function c and so the output is the vector 1 2.

Dominic's crack doesn't define the operator; he simply buried it in a try call, which is also valid R code.

The trick used here means that any future attempt at an almost illegal string will probably have to ban the % character.

Answer 7

Desmos, 9 bytes,

sort(3,2

Banned characters: New Lines

I'm hoping that most people are not familiar with Desmos here, so people wouldn't know what to try.

Note:

An expression in Desmos would be considered an error if it shows a "danger sign" next to the expression, like this:

Answer 8

Rust, 5 Bytes (Safe)

:! =1

Banned Characters:

|!/"'

A nightly compiler is used, you may pass any flags to rustc if you like.

---

A crack by @EasyasPi does work (and is brilliant), but I think because the question says "you must write a program that contains ...", if your code is not designed to run, it isn't a program :)

The intended solution

The idea is to create a local variable that has the never type, call some functions on the integer 1 such that it becomes the never type.

However, with ! as a banned character, we can't simply put the #![feature(never_type)] attribute on the top of the program. We must use an unstable rustc flag that allows us to inject crate-level attributes. The command to compile would be:

cargo rustc -- -Z crate-attr='feature(never_type, core_panic)'

Because closures (|| something) and the use of the ! type outside are restricted, we must operate on the integer literal with provided functions. This is where the core_panic feature comes in and gives us a nice way to transform a &str into !. We know the start and the end, we can just put them together:

use std::io::stdout;
use core::panicking::panic_str;
use std::borrow::Borrow;

fn main() {
    let a:! =1i8.checked_neg().as_ref().map(ToString::to_string).as_ref().map(Borrow::borrow).map(panic_str).unwrap();
}

Answer 9

Vim, 4 bytes, cracked by tail spark rabbit ear

<Esc><Esc>ZQ

This one is a bit more difficult than my other Vim one.

Intended Solution:

i<C-o>:<C-r><Esc><Esc>ZQ

Answer 10

Python 3, 10 bytes, cracked by The Fifth Marshal

?"""?'''?

Banned characters

Alphanumeric, whitespace, and non-ASCII.

---

The intended solution makes use of an interesting quirk in the Python parser.

Here's a hint if you want one:

The hint is that there is no hint. (This isn't a joke. This is actually the hint.)

---

Intended Answer

Hexdump:

00000000: 2300 0a3f 2222 223f 2727 273f  #..?"""?'''?

For some reason,

the Python parser seems to ignore characters following null characters.

So,

it ignores the newline after the #␀, therefore treating the ?"""?'''? as part of the comment.

Fun fact: This was actually posted on the original Find an Illegal String challenge, but when I found a way to get around it, I decided to post it here.

Answer 11

Ruby, 17 bytes, cracked by Dingus

=end
#{"""'}
=end

(no newline at start)

Disallowed charachters: N

Answer 12

Julia, 5 bytes, Cracked by Dingus

?""":

Disallowed charachters: #

Answer 13

Julia, 6 bytes

?""":

There is a zero width space before the :

Disallowed characters: #

Answer 14

Python 3, 13 bytes, Cracked by EasyasPi

int(А,В,С)

Banned Characters: All ascii characters except 2()~+ and newlines. '"#= are banned.

 !"#$%&'*,-./013456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}

The solution makes use of an odd python 3 feature.

Try it online!

Answer 15

nasm, 4 bytes, safe

[al]

Banned characters:

;"`'%#

Solution:

section is, as far as I know, the only thing in NASM which accepts an arbitrary string without quotes.

        section [al]
        section .text
        global _start
_start:
        mov     eax, 60
        syscall

Try it online!

Stop giving me these assembly ones for free. 😔

Answer 16

Python 3, 3 bytes, Cracked by user

I can't believe I missed that obvious loophole! I am adding a slightly revised version of my code that should avoid this.

New Answer, 4 bytes, Cracked by Unrelated String

 1=2

Note: There is a space at the beginning of the code.

Banned characters: All non-ascii characters, quotes, and #.

"'#

Try it online!

Old Answer, 3 bytes, Cracked by user:

1=2

Banned characters: All non-ascii characters, quotes, and #.

"'#

Try it online!

My intended solution for both posts:

foo : 1=2

Answer 17

Javascript, 7 bytes, cracked by Makonede

...void

Javascript, 8 bytes, cracked by Makonede

Note one trailing space

...void 

Banned characters:

• all comments: //, /**/
• all strings: "", ``, ''
• curlies: {}
• brackets: []
• asterisk: *
• the letter w

Clarifications: My cop answer works in a browser environment, but there are probably solutions in Node too.

Answer 18

Ruby, 17 bytes

=end
#{"""'}
=end

Disallowed characters: N,%

This time I made it a bit harder.

Answer 19

Ruby, 18 bytes

=end
#{/"""'}
=end

Disallowed characters: N,%,/

my final variation, hopefully the next solution is the intended one.

Answer 20

Zsh

 
#include <cstdlib> 
#include <iostream> 
 
int main() { 
    srand(time(NULL)); 
    hello(); 
    return rand() % 2; 
} 
 
/* 
  main 
  a=0 
  \ 
  print "$((1/$a))" 
*/ 
 
void hello() std::cout << "Hello, World!" << std::endl; 
 

• Allowed characters: all printable ASCII except blxy<'`$ (lowercase B, L, X, and Y, single-quote, grave, dollar sign)
• Please note all the leading and trailing whitespace.

Probably not too hard but you may learn a lot about the many - shall we say "quirks" - of zsh.

Answer 21

Desmos, 2 bytes, cracked by PkmnQ

Substring:

\

(Note the newline in the beginning)

Banned characters: All alphanumeric characters

abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789

I'm hoping that most people are not familiar with Desmos here, so people wouldn't know what to try.

Note:

An expression in Desmos would be considered an error if it shows a "danger sign" next to the expression, like this:

Answer 22

Python 3, 6 bytes, cracked by EasyasPi

@EasyasPi's crack does work (and I'm dumb for letting it work), but I'm not revealing the original solution yet; I've posted a v2 hopefully preventing any loopholes.

raise

Banned characters

 "'(),.:[\]_{|}

Non-ASCII characters are all banned as well. Try it online or validate it online!

Some cracks that work without the banned chars

'''
raise'''

"""
raise"""

raise SystemExit

raise\
SystemExit

Answer 23

Vim, 3 bytes, cracked by tail spark rabbit ear

<Esc>ZQ

A Vim program doesn't really "error out" per se, but ZQ will exit the current file without saving, so it can't be executed in a valid program, thereby making it "illegal".

This is a bit of an easier one, if you know Vim.

Intended Solution:

i<C-v><Esc>ZQ

Answer 24

Vyxal, 15 bytes, Cracked by lyxal

«Wi«»Wi»`Wi`Wi

Try it Online!

No bans, do what you want. Note that silently erroring at compile-time (Nothing appears in the 'output' box) counts as an error - even the empty program outputs 0...

My intended solution was prepending a [ to just make sure the code isn't run.

Answer 25

JavaScript (THREE.js 105) (Must include canvas element) ~48 bytes

const scene = new THREE.Scene();
scene.add(cube);

Note empty lines Try it!

Banned Characters: All quote characters

/

Answer 26

Pyth, 32 bytes

X$globals()$"imp_print"$mod$

""

Banned characters are:

$\LMN."

Try it online!

Answer 27

Python 3, 7 bytes

"""'''$

(Note no starting or trailing newline.)

Disallowed characters:

#