Cryptography

"Cryptography is the practice and study of techniques for secure communication in the presence of third parties. - Wikipedia "

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

I would suggest these two books for beginners and my sections on cybersecurity click here : first link / /second link  

Caesar Cipher

The Caesar Cipher is a very simple and common encryption method which does not appear often in full-fledged CTFs but forms part of the basis of cryptography. It simply shifts a string of letters a certain number of positions up or down the alphabet.
Let's say we want to encrypt the string hello world to give to our friend whose favorite number is 3. We will shift our string left 3.
Taking the first letter h in our string and going 3 places up the alphabet(as it is a left shift) gives us the letter e. We then start our new, encrypted string with the letter.
Doing so for the whole original string creates a jumbled mess of incomprehensible letters to anyone but the reader with the proper decryption shift:
Original: hello world
Final: ebiil tloia
To let our friend read this, we would send him the final string with the instructions right 3, and either by hand, with a website, or with a script, he would be able to extract our message.

Detecting

Caesar ciphers are usually presented in very low-point tasks, if at all, and can be easy to detect and check for. Strings containing incomprehensibly jumbled letters are possible Caesar ciphers and should be checked.

Solving

There are many approaches to cracking Caesar ciphers, but usually the best way to solve them is to write a script or run the string through a website which will print out all the possible shifts of a string. From those results the most comprehensible and logical solution can be chosen.

Sources/See More

Brute force caeser cipher cracker

Vigenère Cipher

The Vigenère Cipher is a method of encrypting alphabetic text by using a series of different Caesar ciphers based on the letters of a keyword - Wikipedia.

Please read the article on Caesar Ciphers if you haven't already because the Vigenère Cipher is a direct derivative of the former. The Vigenère cipher takes a keyword and applies a certain caeser cipher to it multiple times according to the letters of a keyword.
To-Do Example

Detecting

Vigenère Ciphers appear to be identical to any other substitution cipher, but trying to solve it as Caesar Cipher will not work. Check for this type of cipher if the Caesar Cipher crack does not work.

CTF Example

DEKTHON 2014 had a simple vigenère cipher with no hints and only a line of text:
ucoizsbtkxhtadcg
Solution can be found here.

Sources/See More

Online Vigenère cracker

MD5 Hashing

MD5 is a widely used cryptographic hash function producing a 128-bit (16-byte) hash value, typically expressed in text format as a 32 digit hexadecimal number - Wikipedia.

This system is commonly used to check the integrity of files (like downloads). The way MD5 hashes are created, any slight variation in a file creates a new hash that is completely different than the previous, making changes in files (e.g. corruption in download or tampering) very apparent.
Creating an MD5 hash is very simple, as there are multiple online tools like md5-creator and even a command line tool md5sum which will quickly create a sum from input.

Detecting

MD5 hashes are very standard, as they are always 128 bits, or 32-character strings.

Sources/See More

Easy MD5 cracker

   

    

    we are new but  we proms you to give a best   content we just need you

                        see also steganography

  

 how would need more information look here 

  and form practice cyber security visit this link