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December 21, 2015

# How Symmetric Encryption Works

December 21, 2015

By: HamzaMegahed

December 21, 2015

**Symmetric Encryption**Symmetric encryption or symmetric key or single-key encryption is an encryption system where the encryption and the decryption processes are preformed using the same key.

*Symmetric Encryption Model:***1- Plaintext (P):**The original message or data. The plaintext is an input to the encryption algorithm.

**2- Encryption Algorithm (E):**This algorithm preforms various substitutions and transpositions on the plaintext and produces the ciphertext.

**3- Ciphertext (C):**This is the output produced by the encryption algorithm. The ciphertext is a scrambled message and it appears as a random stream of data.

**4- Encryption Key (K):**Encryption key or secret key is a value that's independent of the plaintext.Encryption key is an input to the encryption algorithm. The encryption algorithm will produces a different with different keys.

**5- Decryption Algorithm (D):**This algorithm is a reverse of the the encryption algorithm. It takes ciphertext and the encryption key as input and produces the plaintext as output.

**Alice wants to send an encrypted message to Bob and both have the secret key, which is generated by the encryption algorithm or by a third-party software. This process will work as follows:1- Encryption algorithm E (on Alice's computer) takes the plaintext P and the secret key K. It generates a ciphertext C.C = E(P,k)2- The ciphertext C will be transferred via the internet.3- Decryption algorithm D (on Bob's computer) takes the ciphertext and the secret key K (the same key) and regenerates the original plaintext P again.P = D(C,K)**

*How Symmetric Encryption Works:**Hint#1:*The encryption key is independent of the plaintext and the encryption algorithm.

*Hint#2:*The sender and receiver must have copies of the encryption key and they must secure that key.

*Hint#3:*We do not need to keep the encryption algorithm secure because it's impractical to decrypt a ciphertext by only using the decryption algorithm. That's the same for the encryption algorithm.

*Hint#4:*Key exchange must be done via a secured channel. Thanks and please post your comments below.