: ※ 引述《wakke (冲阿 去掉C)》之铭言： : 列举两题 : 43. When using public key encryption scheme, : how to let A securely transmit a message to B, : and let B believe that the message is indeed sent by A？ : (A) use A’s public key to encrypt the message, : and then use B’s private key to encrypt the previous encrypted message : (B) use A’s private key to encrypt the message, : and then use B’s public key to encrypt the previous encrypted message : (C) use B’s public key to encrypt the message, : and then use A’s private key to encrypt the previous encrypted message : (D) use B’s private key to encrypt the message, : and then use A’s public key to encrypt the previous encrypted message : (E) none of the above http://0rz.net/350nJ 因为 public/privite key 都是一组 key，都可以用来加解密 只是用一个加密，就要用另一个解密 一般 public key 都是让别人可以取得的 所以加密用对方的 public key 加密 对方收到後就可以用他自己的 private key 解密 而要确定是A传的(这叫做A对他的信签名) A用他自己的 private key 加密，附在信的後面 别人收到後就用 A 的 public key 解密 如果解出来一样，救代表这的确是 A 传的 所以答案是 B，先签名，然後加密 我想 C 是因为签名的讯息留在外面，比较不安全吧(不太确定...) : 31. Which of the following is wrong？ : (A) public key encryption is also called asymmetric key encryption : because the encryption and decryption use different keys : (B) private key encryption is also called symmetric key encryption : because the encryption and decryption use the same keys : (C) public key encryption scheme can be used for digital signature : (D) PGP is used to secure email messages : (E) all of the above are correct http://en.wikipedia.org/wiki/Asymmetric_key_algorithm symmetric 是说加/解密用同一组 key assymmetric 是用不同 key 所以是(B) --

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