Encryption is the process of changing a plaintext(a clear message) into a Ciphertext (Encrypted message)

Decryption is the process of changing a Ciphertext into a plaintext.

Cryptography is the art and science of keeping message secure. It can be known as cryptology or cryptanalysis too.

An encryption function can be represented as E[P] = C

where E stands for Encryption , P Stands for Plaintext and C stands for Ciphertext

In the reverse process, the decryption function can be represented as D[C] = P

where D stands for Decryption, C stands for Ciphertext and P stands for Plaintext

There are 2 general type of key-based algorithms : Symmetric Algorithm and public key algorithms.

The Symmetric Algorithm also known as symmetric Encryption is one that uses a Single key. Other names that are commonly used are secret-key encryption , one key encryption or conventional encryption. This algorithm uses the same key (a single secret key) for both encryption and decryption.

Both the sender and receiver will have to agree on a key before they communicate. An illustration would be the sender lock up a box with a number lock and only the receiver can open it as he knows the key to the lock.

The Public-Key algorithm also known as public-key encryption or asymmetric-key encryption. Each user in this case has two keys instead of one. One is a public key and One is a private key.

The public key is known to everyone which is being hosted on a public key server. The plaintext is first, encrypted using the public key of the receiver and sent to the intended recipient. Upon receiving the message, the receiver decrypt the message using his own Private Key which only he himself knows what it is. The Ciphertext encrypted by the public key of the receiver can only be opened by the Private key of the receiver. It cannot be decrypt with the same Public Key used to encrypt the message.