第67題： 等級(jí)保護(hù)2.0強(qiáng)化了對(duì)外部人員的管理要求，包括外部人員的訪問權(quán)限、保密協(xié)議的管理要求，以下表述中，錯(cuò)誤的是（）。
A.應(yīng)確保在外部人員接入網(wǎng)絡(luò)訪問系統(tǒng)前先提出書面申請(qǐng)，批準(zhǔn)后由專人開設(shè)賬號(hào)、分配權(quán)限,并登記備案
B.外部人員離場(chǎng)后應(yīng)及時(shí)清除其所有的訪問權(quán)限
C.獲得系統(tǒng)訪問授權(quán)的外部人員應(yīng)簽署保密協(xié)議，不得進(jìn)行非授權(quán)操作，不得復(fù)制和泄露任何敏感信息
D.獲得系統(tǒng)訪問授權(quán)的外部人員，離場(chǎng)后可保留遠(yuǎn)程訪問權(quán)限
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第68題： 根據(jù)加密和解密過程所采用密鑰的特點(diǎn)可以將加密算法分為對(duì)稱加密算法和非對(duì)稱加密算法兩類，以下屬于對(duì)稱加密算法的是（）.
A.RSA
B.MD5
C.IDEA
D.SHA-128
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第69題： 移位密碼的加密對(duì)象為英文字母，移位密碼采用對(duì)明文消息的每一個(gè)英文字母向前推移固定key位的方式實(shí)現(xiàn)加密。設(shè)key=6，則明文“SEC”對(duì)應(yīng)的密文為（）
A.YKI
B.ZLI
C.XJG
D.MYW
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第71題： Symmetric-key cryptosystems use the（） key for encryption and decryption of a message,though a message or group of messages may have a different key than others. A significant disadvantage of symmetric ciphers is the key management necessary to use them securely.Each distinct pair of communicating parties must, ideally, share a different key, and perhaps each ciphertext exchanged as well. The number of keys required increases as the square of the number of network members,which very quickly requires complex key management schemes to keep them all straight and secret. The difficulty of securely establishing a secret（）between two communicating parties, when a secure channel doesn't already exist between them, also presents a chicken-and-egg problem which is a considerable practical obstacle for cryptography users in the real world.
Whitfield Dif?ie and Martin Hellman, authors of the first paper on public-key cryptography.
In a groundbreaking 1976 paper, Whitfield Diffie and Martin Hellman proposed the notion of public-key (also, more generally, called asymmetric key) cryptography in which two different but mathematically related keys are used-a public key and a private key. A public key system is so constructed that calculation of one key (the private key) is computationally infeasible（）the other (the public key), even though they are necessarily related. Instead, both keys are generated secretly, as an interrelated pair. The historian David Kahn described public-key cryptography as “the most revolutionary new concept in the field since poly-alphabetic substitution emerged in the Renaissance”.
In public-key cryptosystems,the（）key may be freely distributed,while its paired private key must remain secret. The public key is typically used for encryption, while the private or secret key is used for decryption. Diffie and Hellman showed that public-key cryptography was possible by presenting the Diffie-Hellman key exchange protocol.
In 1978, Ronald Rivest, Adi Shamir, and Len Adleman invented（）,another public-key system.
In 1997, it finally became publicly known that asymmetric key cryptography had been invented by James H. Ellis at GCHQ,a British intelligence organization, and that, in the early 1970s,both the Diffie-Hellman and RSA algorithms had been previously developed(by Malcolm J. Williamson and Clifford Cocks, respectively).
(1) A. different
B. same
C.public
D. private
(2)A. plaintext
B. stream
C.ciphertext
D.key
(3)A.from
B. in
C.to
D.of
(4)A.public
B.private
C.symmetric
D.asymmetric
(5) A.DES
B.AES
C.RSA
D.IDEA
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