Question

I have a string that looks like YB[Xf`lbt+glo

What is the encryption used to encrypt this string?

Answer 1

I somewhat disagree with all the negative comments. While more data would of course help, it is still quite possible to make educated guesses based on the length and charset in the sample string. Some ideas off the top of my hat:

• The sample has the same length as a traditional DES crypt(1) hash, albeit unexpected characters. Could be a DES crypt(1) hash with some custom output character set. Not terribly likely but possible.
• The sample could be base85/ascii85 encoded, which is 80 bits of raw data. This is a rather unusual size. It could theoretically be the output of a hash function with digest size 80 bits, or longer and shortened to 80 bits, or of a block cipher with block size 80 bits (e.g. REDOC). More likely perhaps is a stream cipher.
• Part of the data could be a salt or IV, assuming base85 it could quite reasonably be 16 bits of IV and a ciphertext block of 64 bits.
• It could be just 80 bits of random data as e.g. a session identifier.

That’s about all that can be reasonably squeezed out of the sample above I think. Not much, but it’s a start. We’d need other data and information to be able to judge what is more or less likely and to confirm or rule out some of the possibilities.

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(edit after the solution was posted)

For those who are interested, this is how to decode the encoded string using code from the packed JS code and running it e.g. in spidermonkey or ideone.com:

function R(t) {
    var f = "";
    for (var d = 0; d < t.length; d++) {
        f += String.fromCharCode(t.charCodeAt(d) ^ (1 + (t.length - d) % 32));
    }
    return f;
}
print(R("YB[Xf`lbt+glo"));

it returns:

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