Gotta Decrypt Them All

253 solves / 175 points

Source files and Solve Script: CSAW-Quals/crypto/Gotta Decrypt Them All

Attack Idea

STEP 1: Identify the Morse encoded string

STEP 2: Decrypt to get Integers

STEP 3: Convert them to ASCII characters

STEP 4: Identify Base64 and decode it to get RSA parameters and encrypted message

STEP 5: Check the small public exponent (e) and take the eth root to get the message

Why STEP 5 works?

In practice, we pick the RSA parameters and the message such that$m^{e} \geq n$. If we use a small message and a small exponent then it just becomes$c = m^{e}$ and we can directly calculate$m = \sqrt[e]{}c$ to get back our message.