des加密算法verilog实现，包括模块定义，端口说明-des Encryption and decryption

用verilog实现的DES(Data Encryption Standard数据加密标准)，把64位明文输入变为64位密文输出块。-Using DES (Data Encryption Standard Data Encryption Standard) verilog to achieve, the 64 plaintext input into 64 output ciphertext block.