**What is block cipher?**

A block cipher is a symmetric cryptographic algorithm that works on a block of data of a fixed size using a shared secret key. Plain text is used during encryption and the resulting encrypted text is called ciphertext. The same key is used both for encrypting the plaintext and for decrypting the ciphertext.

The block cipher encrypts / decrypts your input one block at a time instead of one bit at a time using a shared secret key. The block is fixed in size; Otherwise, padding is required. This algorithm is symmetrical. During encryption, it uses the shared key to convert its plain text input into encrypted text (encrypted text). During decryption, it uses the same key to transform the ciphertext back into the original plaintext. The length of the output corresponds to the input.

Well-known implementations of the block encryption algorithm are the Data Encryption Standard (DES), TripleDES and the Advanced Encryption Standard (AES).

The counterpart of block cipher is the stream cipher, which works on its input one bit at a time, also using a common key.

An alternative to the block cipher algorithm is public key cryptography or asymmetric cryptography. This algorithm uses a public key to encrypt plain text and a private key to decrypt the resulting ciphertext.