13 -- picoCTF Crypto Challange (Easy)

Challenge Overview

• Event: PicoCTF 2019
• Challenge Name: 13
• Category: Cryptography
• Difficulty: Easy

Challenge Description:

Cryptography can be easy, do you know what ROT13 is? cvpbPGS{abg_gbb_onq_bs_n_ceboyrz}

Answer: picoCTF{n**********************em}

Introduction:

“13” is one of the mostinteresting cryptography challenge that tests your understanding of classic cryptographic ciphers.

Challenge Walkthrough:

The challenge presents an encoded text and hints that it is encrypted using a simple substitution cipher. The name “13” itself is a major clue pointing towards ROT13, a well-known shift cipher in cryptography.

ROT13 (Rotate by 13 places) is a special case of the Caesar cipher, where each letter in the alphabet is shifted forward by 13 places. If a letter goes past ‘Z’, it wraps around to the beginning of the alphabet. Since 13 is half of 26 (total letters in the English alphabet), applying ROT13 twice returns the original text. For example:

Rehema in ROT13 becomes Erurzn

To decode the given text, you can use:

1. Online ROT13 Decoders: Simply paste the given text into an online ROT13 decoder like https://cryptii.com/pipes/rot13-decoder or https://rot13.com/ as shown below: