I try to find the encoding of a string. I thought at first it was Base64, but actually not, it seems ...

Let me explain quickly. For a exercise, I have to decode the following string: ZXJpcjRxbnJ1YnZxbmU=

I have to use a form on a website (I can't distribute the URL) that allows me to generate an encoded string from what I entered.

For example, if I type the letter A, I have this: Tg== For B: Tw== And fortunately, the value remains the same (so no grain of salt).

Can you help me? I'm on it for a while and I still have not solved my problem..

Thanks. o/

closed as off-topic by TildalWave, Jens Erat, Xander, RoraΖ, schroeder Jan 15 '15 at 18:19

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Questions asking us to break the security of a specific system for you are off-topic unless they demonstrate an understanding of the concepts involved and clearly identify a specific problem." – TildalWave, Jens Erat, Xander
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  • How do you know it is not Base64? Have you been told that when you decode the string it will reveal something meaningful in the English language? Or was the encoded string you posted generated from some string you entered on the form, so you know the original version of it and only need to determine what encoding scheme was used? – MoonPoint Jan 11 '15 at 18:21
  • This string is a password encoded in an unknown manner . The goal is to find how to decode this string , knowing how to encode it must surely be fairly generic and without salt. Whether this string was encoded in base64 , I went on a site that just allowed to encode base64 and I compared the encoding of the letter A base64 (QQ==) against the unknown encoding: Tg== – Pouette Jan 11 '15 at 18:57
  • Isn't this offtopic here? Sounds more suited for stackoverflow. – sashoalm Jan 15 '15 at 13:04

By looking at A= "Tg==" and B= "Tw==" and base 64 decode these values you'll get A= "N" and B= "O" which triggered me as it looks like some sort of substitution.

In your case they used double encoding because as it turned out, it is ROT13, which actually stands for ROTate 13 times:

enter image description here

Now in order to decode your message, you'll first have to base 64 decode the encoded string and then decode the result from ROT13.

ROT13 Decoder: http://rot13-encoder-decoder.waraxe.us/

  • Thank for your response ! So I followed your instructions well. As I explained, I just have to me a form that allows me to encode any string to test. So I used, and surprisingly, the chain is relatively close, but not completely. The initial channel to decode :ZXJpcjRxbnJ1YnZxbmU= and the encoded again to verify :ZW5xdmJ1cm5xNHJpcmU= – Pouette Jan 11 '15 at 19:54
  • Yeah !!! You were right, but in fact they base64 encoded twice and rot13 . Thank you to you !! – Pouette Jan 11 '15 at 20:18

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