Cryptography is an entire field dedicated to secure communication! It is a very deep and complex field, but we will cover some of the basics here.
Thousand years ago Julius Caesar simplest form of encyption Caesar Cipher.
Caesar Cipher
In Caesar Cipher, each letter in the plaintext is replaced by a letter some fixed number of positions down the alphabet. For example, with a shift of 3, the message DOG will be replaced by GRJ.Since it is very easy to detect it by finding all possible shifts, it is not a very secure encryption algorithm.
Substitution Cipher
Similar to the Caeser cipher, substitution ciphers encrypt messages by substituting each letter in the message with a different one, according to some alphabet.But we substitute each letter with a different one, not just shifted by a fixed number of positions. For example: A -> D B -> F C -> G Now the message ABC would be encrypted as DFG.
It is also not a very secure encryption algorithm, because it is very easy to detect the pattern and decrypt the message using frequency analysis since we know that in English alphabet, not all characters are distributed evenly.
Vigenere Cipher
Vigenere cipher is a method of encrypting alphabetic text. It uses a simple form of polyalphabetic substitution. A polyalphabetic cipher is any cipher based on substitution, using multiple substitution alphabets .The encryption of the original text is done using the Vigenère square or Vigenère table. In this cipher we use a key for encrypting plaintext and the key is repeated as many times as necessary to encrypt the plaintext.And encryption is done by using the Vigenère square or Vigenère table.You can read more about it GFG or Wikipedia.
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