Final answer:
DES uses a 64-bit block size and a 56-bit key size. The block size refers to the size of the data that can be encrypted or decrypted at once, while the key size determines the length of the encryption key.
Step-by-step explanation:
DES (Data Encryption Standard) uses a 64-bit block size and a 56-bit key size. The actual key is 56 bits, but there are 8 parity bits added to make a total of 64 bits. However, only 56 bits are used for encryption and decryption, while the remaining 8 bits are used for error checking.
The block size refers to the size of the data that can be encrypted or decrypted at once. In the case of DES, each block consists of 64 bits. This means that a 64-bit block of plaintext is divided into 8 8-bit sub-blocks and processed through several rounds of encryption.
The key size determines the length of the encryption key that is used to transform the plaintext into ciphertext. In DES, the key size is 56 bits, which means there are 2^56 possible key combinations. However, due to the advances in computing power, DES is now considered relatively insecure and has been replaced by more secure encryption algorithms.