[ryan-c]

There are 64 bits of randomness (however, they come from Math.random which is not so good...).

The encrypted text produced by this has a distinct signature - all message will contain "U2FsdG". Here's how we break this if you're Google/can force Google to do stuff:

1) Detect messages containing that OpenSSL 'magic number'

2) If detected, push something like this:

    // Should check to see if GibberishAES exists to avoid errors if it doesn't...
    // Grab target function as a string
    var keycode = '' + GibberishAES.openSSLKey;
    // Inject something evil
    keycode = keycode.replace('key = result.slice(0, 4 * Nk);','key = result.slice(0, 4 * Nk); for (var pos = 1; pos < 4 * Nk; pos++) { result[pos] = 0; };');
    keycode = 'EvilGibberish = {}; EvilGibberish.openSSLKey = ' + keycode;
    // Execute the modified code to generate the new object
    eval(keycode);
    // Replace the 'good' keygen routine with the 'evil' one
    GibberishAES.openSSLKey = EvilGibberish.openSSLKey;

This will zero all but the first 32 bits of the AES key, allowing easy brute forcing.

Note that this is based on something I wrote for a CTF, and I haven't tested it specifically against GibberishAES, but the technique works.