Block cipher

A block cipher is a cipher in which encryption is performed on a fixed-length block of characters from the plaintext. This cipher technique is widely used to implement encryption on bulk data. The usual block sizes are 64 bits, 128 bits, and 256 bits. For example, a 64-bit block cipher will take 64-bit plaintext as input and give out 64-bit ciphertext. The plaintext will pad some of the blocks in case some of the plaintext falls short of filling a block. Because the keys used in block ciphers are considerably long, they are robust against brute-force attacks. These ciphers are also the building blocks of other cryptographic protocols, such as hash functions and random number generators. Data Encryption Standard (DES), Advanced Encryption Standard (AES), International Data Encryption Algorithm (IDEA), and Blowfish are some popular block cipher algorithms.