PicoCTF 2017 – computeRSA

Another day, another challenge.

Today’s blog post will explore solving the “computeRSA” challenge in the PicoCTF challenge.

Let’s get started.

Clicking on the challenge we see the following:

OK we need do a calculation for the RSA algorithm. Since we have the encrypted number, then we need to do the decryption.

Let’s look at the hints.

We have the decrypted formula.

So the formula: (150815) ^ 1941 mod 435979

Let’s go to Google and use a python interpreter to find the decrypted number.

Going to the following link we’re presented with the interpreter.

Entering the formula in the interpreter we get the following:

Entering this number as the flag we’ve acquired 50 points!