第67題： 等級保護2.0強化了對外部人員的管理要求，包括外部人員的訪問權限、保密協(xié)議的管理要求，以下表述中，錯誤的是（）。
A.應確保在外部人員接入網(wǎng)絡訪問系統(tǒng)前先提出書面申請，批準后由專人開設賬號、分配權限,并登記備案
B.外部人員離場后應及時清除其所有的訪問權限
C.獲得系統(tǒng)訪問授權的外部人員應簽署保密協(xié)議，不得進行非授權操作，不得復制和泄露任何敏感信息
D.獲得系統(tǒng)訪問授權的外部人員，離場后可保留遠程訪問權限
答案解析與討論：www.jazzmuze.com/st/5023718231.html

第68題： 根據(jù)加密和解密過程所采用密鑰的特點可以將加密算法分為對稱加密算法和非對稱加密算法兩類，以下屬于對稱加密算法的是（）.
A.RSA
B.MD5
C.IDEA
D.SHA-128
答案解析與討論：www.jazzmuze.com/st/5023825249.html

第69題： 移位密碼的加密對象為英文字母，移位密碼采用對明文消息的每一個英文字母向前推移固定key位的方式實現(xiàn)加密。設key=6，則明文“SEC”對應的密文為（）
A.YKI
B.ZLI
C.XJG
D.MYW
答案解析與討論：www.jazzmuze.com/st/502396132.html

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
答案解析與討論：www.jazzmuze.com/st/5024120248.html