DES uses a block size of 64 bits. NIST has mandated a block size of 128 bits for a successor symmetric-key block cipher to improve security. NIST is seeking to establish a successor symmetric-key block cipher to DES by 2001. Still widely used for encrypting data sent between banks. For example, DES uses a 56-bit key, which means there are 256 possible keys.
Longer keys result in encryption that is more resistant to brute force attacks.
Block ciphers bundle data into blocks of a certain length and encrypt each block. Stream ciphers encrypt data bit by bit. Currently, these techniques are the most effective methods of attacking block ciphers. Both rely on using plaintext-ciphertext pairs to find the key. Compared with brute-force attack, these can break certain block ciphers with fewer computing resources.