There are two types of key technology：private key and public key．Private-key encryption methods are called(1)ciphers，information is encrypted with(2)both the sender and receiver hold privately．Public—key encryption methods are called(3)ciphers，(4)created for each user，encryption key and decryption key are(5)． (1)A．synchronous B．asynchronous C．symmetric D．asymmetric (2)A．a key B．two keys C．three keys D．four keys (3)A．synchronous B．asynchronous C．symmetric D．asymmetric (4)A．two related keys are B．a key is C．two unrelated keys are D．three keys are (5)A．same B．different C．difference D．some 答案：(1)C (2)A (3)D (4)A (5)B 解析：有两种加密技术：私有密钥和公开密钥。私有密钥加密方法被称为对称密钥加密，在发送者和接受者之间的信息共同具有同一个密钥，公开密钥加密方法被称为非对称密钥加密，对于每一个使用者，都建立两个相关的加密与解密密钥，但它们不同。