Re: [問題] 可以解釋一下public key 跟 private k …
: ※ 引述《wakke (衝阿 去掉C)》之銘言:
: 列舉兩題
: 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
因為 public/privite key 都是一組 key,都可以用來加解密
只是用一個加密,就要用另一個解密
一般 public key 都是讓別人可以取得的
所以加密用對方的 public key 加密
對方收到後就可以用他自己的 private key 解密
而要確定是A傳的(這叫做A對他的信簽名)
A用他自己的 private key 加密,附在信的後面
別人收到後就用 A 的 public key 解密
如果解出來一樣,救代表這的確是 A 傳的
所以答案是 B,先簽名,然後加密
我想 C 是因為簽名的訊息留在外面,比較不安全吧(不太確定...)
: 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 是說加/解密用同一組 key
assymmetric 是用不同 key
所以是(B)
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