帮忙翻译下面的英文,手工的,不要机器翻译
Common symmetric key encryption algorithms include the Data Encryption Standard (DES), Triple-DES (3DES), and the Advanced Encryption Standard (AES). These algorithms are block ciphers, meaning that they take a block of symbols of size n as input and output a block of symbols of size n. DES was published in 1975 and developed as the U.S. standard for unclassified applications in 1977 [Stinson 2002].
DES uses a key size of 56 bits and a block size of 64 bits. The main criticism of DES today is that the 56-bit key length is too short. With newer CPUs, the key space of 256 can be enumerated. Even with machines in 1998, a machine called the “DES Cracker” could find a DES key in 56 hours.