模仿CA颁发证书模式，模拟证书颁发与认证。并假设Alice给Bob发送加密后的文档及文档的签名，Bob验证Alice证书的正确性和加密文档的正确性并最终解密文档。执行顺序为CA_Key-->CA-->Alice-->拷贝Alice的证书和加密文档给Bob-->Bob-Imitation of the CA that issued the certificate mode, analog certification and certification. And assume