Cryptography is the practice and study of techniques for secure communication in the presence of third parties. Cryptography is a branch of mathematics that is responsible for encrypting a message in a communication to transmit confidential information through the web and to protect our privacy. Cryptography has been present throughout history in Roman times with the famous Caesar cipher and even earlier as the use of Scythian. Also in wars, the cryptography was essential to communicate for example, the Lorenz cipher in World War II.

In the case of CTFs, the goal is usually to crack cryptographic algorithms to reach the flag.

Some tools/tips that you can use:

• Analysis of which decoder it can be: https://www.boxentriq.com/code-breaking/text-analysis
• CyberChef: https://gchq.github.io/CyberChef/
• https://www.dcode.fr/
• If it is in Morse code format and it isn’t, try substituting 1’s and 0’s for the dots and dashes. It could be binary or bacon.
• MD5 decrypt: https://www.md5online.org/md5-decrypt.html
• ROT13 Cipher: https://www.rot13.com/
• Caesar cipher https://www.nayuki.io/page/automatic-caesar-cipher-breaker-javascript
• Substitution cipher: https://quipqiup.com/
• Vigenere - Blaise cipher: https://www.guballa.de/vigenere-solver - https://www.mygeocachingprofile.com/codebreaker.vigenerecipher.aspx
• Fernet decoder: https://asecuritysite.com/encryption/ferdecode
• Malbolge esoteric programming language: http://malbolge.doleczek.pl/
• To read from left to right: http://string-functions.com/reverse.aspx
• Some esoteric programming languages: https://en.wikipedia.org/wiki/Esoteric_programming_language
• RSA: https://github.com/telnet22/simple_rsa/blob/master/rsa.py - https://github.com/Masrt200/WoC2k19 -https://github.com/Ganapati/RsaCtfTool
• And more… (Search on Google for clues, there are millions of types of encryption!)

Some websites to practice crypto:

• https://www.mysterytwisterc3.org/en/
• https://cryp.toc.tf/
• https://cryptohack.org/