A block cipher is an algorithm used in cryptography. It is based on a concept called an iterated product cipher, in which multiple encryption procedures are performed on fixed-length groups of bits called blocks. Each round of encryption makes unauthorized decryption progressively more difficult for a third party; effectively eliminating the possibility of the encryption being broken by brute force.
The block cipher method was first proposed by Claude Shannon in 1949 in an influential paper called Communication Theory of Secret Systems. They are a central component of many widely-used encryption ciphers such as DES and AES.