Frequency analysis is the study of the frequency of letters or groups of letters occuring next to each other. The most ancient description for what we know was made by Al-Kindi, dating back to the IXth century. This attack is used to break monoalphabetic ciphers, which work by simple and fixed substitution of letters. We now, that if the a in plaintext is encrypted to x letter, everytime in the ciphertext that x will convert to a.
PicoCTF - SmallRSA
You intercepted a single message. However, it appears to be encrypted. Can you decrypt it? Message
PicoCTF - ComputeRSA
RSA encryption/decryption is based on a formula that anyone can find and use, as long as they know the values to plug in. Given the encrypted number 150815, d = 1941, and N = 435979, what is the decrypted number?
PicoCTF - Broadcast
You stumbled upon a group Message. Can you figure out what they were sending? The string sent is ascii encoded as a hex number (submit the ascii string as the flag)