Symmetric， or private-key， encryption is based on a secret key that is shared by both communcating parties. The（ ）party uses the secret key as part of the mathematical operation to encrypt（ ）text to cipher text. The receiving party uses the same secret key to decrypt the cipher text to plain text. Asymmetric， or public-key， encryption uses two different keys for each user： one is a（ ）key known only to this one user； the other is a corresponding public key， which is accessible to anyone. The private and public keys are mathematically related by the encryption algorithm. One key ia used for encyption and the other for decryption， depending on the nature of the communication service being implemented. In addition， public key encryption technoligies allow digital（ ）to be placed on messages. A digital signature uses the sender’s private key to encrypt some portion of the message. When the message is received， the receiver uses the sender’s（ ）key tp decipher the digital signature to verify the sender's identity.
问题1
正确答案CADBC,对称密钥或私钥的加密基于通信双方共享的密匙。发送方使用密匙进行数学操作来将明文变成密文。接收方使用同样的密匙将密文解析为明文。非对称密钥或公钥的加密针对用户使用两种不同的密钥：一种是用户的专用私钥；另一种是一个任何用户都可见的通讯公钥。私钥和公钥在数学上都和加密算法有关。根据所实施的通信服务本质的不同，一个密钥用来加密而另一个用来解密。另外，公钥加密技术允许消息中添加数字签名。当这则消息被接受时，接受者使用发送者的密钥来解析数字签名，以识别发送者的身份。
