its perfect Digital signing application. with document !!! alice/bob

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

证书制作， 数字签名，证书颁发，身份识别。-Imitate CA certificate model, simulate a certificate and the authentication. And assumed that Alice to Bob send encrypted document after document and signature, Bob verify the correctness of the Alice certificate and the correct