3 ms·

Encode any JavaScript with only six characters

17 points by antichaos 15y ago

LeafStorm 15y ago
This is an...interesting hack. However, it's not entirely clear how it works.
- dlytle 15y ago
  Probably similar principles to Brainfuck. Check Wikipedia for an explanation of Brainfuck, I can't come close to doing it justice.
  - LeafStorm 15y ago
    I know how that language works, I'm just surprised that this is capable of pulling off function calls, string concatenations, etc. etc. using only ridiculous type coercions.
  - baddox 15y ago
    Any similarity is coincidental. This hack isn't doing anything semantic or syntactic to the code you provide: it's just encoding the string you provide into an equivalent string in another alphabet. The two alphabets happen to be identical in JavaScript. For example, `+[]` equals the integer 0 (apparently the unary plus operator coerces the empty array to a boolean then converts to an integer), and `![]` of course equals the boolean false. Furthermore, JavaScript does some weird type coercion, so `false + []` equals the string "false". Replace the boolean false with `![]`, so `![] + []` equals the string "false". Now, if we need the letter "f" we just do `"false"[0]`, encoded as `(![] + [])[+[]]`. Remove spaces, and you can see that `(![]+[])[+[]]` is equivalent to "f". People have figured out how to get tons of characters from small initial character sets. See this: http://sla.ckers.org/forum/read.php?24,33349,33405 http://sla.ckers.org/forum/read.php?24,33349,33405
jr62 15y ago
On Chrome 14 (Linux), when I click "eval" it doesn't show the alert dialog. Even leaving the default text there. It's an interesting concept though, would definitely be good to see an explanation of how it works.
- quanticle 15y ago
  If I try copying and pasting the encoded source into Chrome's JS console, it gives the following error: TypeError: Array.prototype.sort called on null or undefined. I would be interested to see what exactly it's doing, and how alert("Hello World"); gets mangled to call Array.prototype.sort(). EDIT: I should note that I get this error no matter what code I put in. I think Chrome's Javascript interpreter is somehow interpreting some of that boilerplate as a call to Array.prototype.sort() somehow.
laserDinosaur 15y ago
Oddly I could not get it to work in chrome or firefox, and it managed to crash all my tabs in chrome. The other demos seem to work much better though: http://utf-8.jp/public/jjencode.html http://utf-8.jp/public/jjencode.html
brayker 15y ago
Want to know how it works? view-source:http://utf-8.jp/public/jsfuck.html http://utf-8.jp/public/jsfuck.html
endtwist 15y ago
For those curious, the trick works by creating strings (such as "NaN" or "Infinity") and integers, then treating the strings as arrays and selecting out characters. The [], +, ! and () are assembled in sequences that result in these strings/integers (thanks to Javascript's liberal language rules). Here's a dictionary/more information: http://sla.ckers.org/forum/read.php?24,33349,33405 http://sla.ckers.org/forum/read.php?24,33349,33405
jballanc 15y ago
While this might seem like nothing more than a neat parlor trick, there is an important lesson to take away: NEVER, under ANY circumstances insert untrusted values into your scripts. No amount of white-listing/black-listing/escaping/etc. will protect you.
hasegawayosuke 15y ago
In the past, this was worked on Chrome and Firefox. but now JSF*ck is worked only Opera. Sorry, but I have no patience to fix it. -- Yosuke HASEGAWA / utf-8.jp

17 points by antichaos 15y ago

LeafStorm 15y ago

This is an...interesting hack. However, it's not entirely clear how it works.

dlytle 15y ago
Probably similar principles to Brainfuck. Check Wikipedia for an explanation of Brainfuck, I can't come close to doing it justice.
- LeafStorm 15y ago
  I know how that language works, I'm just surprised that this is capable of pulling off function calls, string concatenations, etc. etc. using only ridiculous type coercions.
- baddox 15y ago
  Any similarity is coincidental. This hack isn't doing anything semantic or syntactic to the code you provide: it's just encoding the string you provide into an equivalent string in another alphabet. The two alphabets happen to be identical in JavaScript. For example, `+[]` equals the integer 0 (apparently the unary plus operator coerces the empty array to a boolean then converts to an integer), and `![]` of course equals the boolean false. Furthermore, JavaScript does some weird type coercion, so `false + []` equals the string "false". Replace the boolean false with `![]`, so `![] + []` equals the string "false". Now, if we need the letter "f" we just do `"false"[0]`, encoded as `(![] + [])[+[]]`. Remove spaces, and you can see that `(![]+[])[+[]]` is equivalent to "f". People have figured out how to get tons of characters from small initial character sets. See this: http://sla.ckers.org/forum/read.php?24,33349,33405 http://sla.ckers.org/forum/read.php?24,33349,33405

jr62 15y ago

On Chrome 14 (Linux), when I click "eval" it doesn't show the alert dialog. Even leaving the default text there. It's an interesting concept though, would definitely be good to see an explanation of how it works.

quanticle 15y ago
If I try copying and pasting the encoded source into Chrome's JS console, it gives the following error: TypeError: Array.prototype.sort called on null or undefined. I would be interested to see what exactly it's doing, and how alert("Hello World"); gets mangled to call Array.prototype.sort(). EDIT: I should note that I get this error no matter what code I put in. I think Chrome's Javascript interpreter is somehow interpreting some of that boilerplate as a call to Array.prototype.sort() somehow.

laserDinosaur 15y ago

Oddly I could not get it to work in chrome or firefox, and it managed to crash all my tabs in chrome. The other demos seem to work much better though: http://utf-8.jp/public/jjencode.html http://utf-8.jp/public/jjencode.html

brayker 15y ago

Want to know how it works? view-source:http://utf-8.jp/public/jsfuck.html http://utf-8.jp/public/jsfuck.html

endtwist 15y ago

For those curious, the trick works by creating strings (such as "NaN" or "Infinity") and integers, then treating the strings as arrays and selecting out characters. The [], +, ! and () are assembled in sequences that result in these strings/integers (thanks to Javascript's liberal language rules). Here's a dictionary/more information: http://sla.ckers.org/forum/read.php?24,33349,33405 http://sla.ckers.org/forum/read.php?24,33349,33405

jballanc 15y ago

While this might seem like nothing more than a neat parlor trick, there is an important lesson to take away: NEVER, under ANY circumstances insert untrusted values into your scripts. No amount of white-listing/black-listing/escaping/etc. will protect you.

hasegawayosuke 15y ago

In the past, this was worked on Chrome and Firefox. but now JSF*ck is worked only Opera. Sorry, but I have no patience to fix it. -- Yosuke HASEGAWA / utf-8.jp