Symmetric encryption or symmetric key or single-key encryption is an encryption system which the encryption and the decryption processes are preforms using the same key.
SymmetricÂ Encryption Model: Plaintext (P) The original message or data, the plaintext is an input to the encryption algorithm. Encryption algorithm (E) This algorithm preforms various substitution and transposition on the plaintext and produces the ciphertext. Ciphertext (C) Is the output produced by the encryption algorithm , the ciphertext is scrambled message and it is appears like a random stream of data.

As we mentioned earlier, the basic of all encryption techniques are based on 2 techniquesÂ Substitution and Transposition and we can also use a combination of both of them.
Substitution Encryption techniques Substitution is an encryption technique which elements in the plaintext are replaced or mapped with another elements.
There are many types of the substitution techniques such as Monoalphabetic Cipher and Polyalphabetic Cipher
Monoalphabetic Cipher We will drive an example of monoalphabetic cipher called (Caesar cipher) Caesar Cipher :