《计算机专业英语》谢希仁第二版第10章讲义.ppt

10.7 Public Encryption In many encryption schemes, the key must be kept secret to avoid compromising security. One particularly interesting encryption technique assigns each user a pair of keys. One of the user’s keys, called the private key, is kept secret, while the other, called the public key, is published along with the name of the user, so everyone knows the value of the key. The encryption function has the mathematical property that a message encrypted with the public key cannot be easily decrypted except with the private key, and a message encrypted with the private key cannot be decrypted except with the public key. 在很多加密方法中，为了避免危及安全，必须保持密钥是必威体育官网网址的。但有一种十分有趣的加密方法称为公共密钥加密法，它给每个用户分配两把密钥：一个称为私有密钥，是必威体育官网网址的；另一个称为公共密钥，随用户名一起公布，因而是众所周知的。该方法的加密函数必须具备如下数学特性：用公共密钥加密的消息除了使用相应的私有密钥外很难解密；同样，用私有密钥加密的消息除了使用相应的公共密钥外很难解密。 10.7 Public Encryption The relationships between encryption and decryption with the two keys can be expressed mathematically. Let M denote a message, pub-u1 denote user 1’s public key, and prv-u1 denote user 1’s private key. Then M=decrypt (pub-u1, encrypt (prv-u1, M )) and M=decrypt (prv-u1, encrypt (pub-u1, M )) 使用这两把密钥加密与解密的关系表示成数学形式如下：假设M表示一条消息，pub-u1表示用户1的公共密钥，prv-u1表示用户1的私有密钥，那么有 M=decrypt (pub-u1, encrypt (prv-u1, M )) 和 M=decrypt (prv-u1, encrypt (pub-u1, M )) 10.7 Public Encryption Revealing a public key is safe because the functions used for encryption and decryption have a one-way property. That is, telling someone the public key does not allow the person to forge a message that appears to be encrypted with the private key. 公布公共密钥是安全的，因为这种方法的加密和解密函数具有单向性。也就是说，仅知道了公共密钥并不能伪造由相应私有密钥加密过的消息。 10.7 Public Encryption Public key encryption can be used to guarantee confidentiality. A sender who wishes a message to remain private uses the receiver’s public key to encrypt the message. Obtaining a copy of the message as it passes across the network does not enable someone to read the contents because decryption requires the receiver’s private key. Thus, the scheme