Block Cipher

A block cipher is an encryption scheme that breaks up the plaintext message into strings (blocks) of a fixed length $n$ and encrypts one block at a time.

• Encryption: takes in input one block of $n$ bits of plaintext and key of $k$ bits, producing an output of one block of ciphertext of $n$ bits.
• Decryption: takes in input one block of $n$ bits of ciphertext and a key of $k$ bits, producing an output of one block of plaintext of $n$ bits.