Block Cipher

A Block Cipher is used to encrypt or decrypt data that has been organised into a fixed bit-length, called a block. DES, Triple DES, AES, NOEKEON and Madryga are examples of block ciphers.

The strength of a block cipher depends on the length of the secret key that is used with it. The choice of bit-length does not affect the strength of the encryption algorithm. However it can affect performance because if the source data is shorter than the selected bit-length, then empty bits need to be padded out, reducing efficiency.

Block ciphers may also be used with other cryptographic tools, such as hash functions and pseudo-random number generators. They are often paired up with a stream cipher to handle the handshake when setting up a communication link and they are routinely used to handle encryption of bulk data.

A secure block cipher can be converted into a CSPRNG by running it in counter mode.