第66題： 目前網(wǎng)絡(luò)安全形勢日趨復(fù)雜，攻擊手段和攻擊工具層出不窮，攻擊工具日益先進, 攻擊者需要的技能日趨下降。以下關(guān)于網(wǎng)絡(luò)攻防的描述中，不正確的是（  ）。
A.嗅探器Sniffer工作的前提是網(wǎng)絡(luò)必須是共享以太網(wǎng)
B.加密技術(shù)可以有效抵御各類系統(tǒng)攻擊
C.APT的全稱是高級持續(xù)性威脅
D.同步包風暴(SYN Flooding)的攻擊來源無法定位
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第67題： （  ）攻擊是指借助于客戶機/服務(wù)器技術(shù),將多個計算機聯(lián)合起來作為攻擊平臺，對一個或多個目標發(fā)動DoS攻擊，從而成倍地提高拒絕服務(wù)攻擊的威力。
A.緩沖區(qū)溢出
B.分布式拒絕服務(wù)
C.拒絕服務(wù)
D. 口令
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第68題： 如果對一個密碼體制的破譯依賴于對某一個經(jīng)過深入研究的數(shù)學(xué)難題的解決，就認為相應(yīng)的密碼體制是（  ）的。
A.計算安全
B.可證明安全
C.無條件安全
D.絕對安全
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第70題： 基于公開密鑰的數(shù)字簽名算法對消息進行簽名和驗證時，正確的簽名和驗證方式是（  ）。
A.發(fā)送方用自己的公開密鑰簽名，接收方用發(fā)送方的公開密鑰驗證
B.發(fā)送方用自己的私有密鑰簽名，接收方用自己的私有密鑰驗證
C.發(fā)送方用接收方的公開密鑰簽名，接收方用自己的私有密鑰驗證
D.發(fā)送方用自己的私有密鑰簽名，接收方用發(fā)送方的公開密鑰驗證
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第71題： The modern study of symmetric-key ciphers relates mainly to the study of block ciphers and stream ciphers and to their applications. A block cipher is, in a sense, a modern embodiment of Alberti's polyalphabetic cipher: block ciphers take as input a block of （71 ）and a key, and output a block of ciphertext of the same size. Since messages are almost always longer than a single block, some method of knitting together successive blocks is required. Several have been developed, some with better security in one aspect or another than others. They are the mode of operations and must be carefully considered when using a block cipher in a cryptosystem.
The Data Encryption Standard (DES) and the Advanced Encryption Standard (AES) are( 72 )designs which have been designated cryptography standards by the US government (though DES's designation was finally withdrawn after the AES was adopted). Despite its deprecation as an official standard, DES (especially its still-approved and much more secure triple-DES variant) remains quite popular; it is used across a wide range of applications, from ATM encryption to e-mail privacy and secure remote access. Many other block ciphers have been designed and released, with considerable variation in quality. Many have been thoroughly broken. See Category: Block ciphers.
Stream ciphers, in contrast to the ‘block’type, create an arbitrarily long stream of key material, which is combined ( 73 )the plaintext bit-by-bit or character-by-character, somewhat like the one-time pad. In a stream cipher, the output( 74 )is created based on an internal state which changes as the cipher operates. That state change is controlled by the key, and, in some stream ciphers, by the plaintext stream as well. RC4 is an example of a well-known, and widely used, stream cipher; see Category: Stream ciphers.
Cryptographic hash functions (often called message digest functions) do not necessarily use keys, but are a related and important class of cryptographic algorithms. They take input data (often an entire message), and output a short fixed length hash, and do so as a one-way function. For good ones, ( 75 ) (two plaintexts which produce the same hash) are extremely difficult to find.
Message authentication codes (MACs) are much like cryptographic hash functions, except that a secret key is used to authenticate the hash value on receipt. These block an attack against plain hash functions.
（71）
A.plaintext
B.ciphertext
C.data
D.hash
（72）
A.stream cipher
B.hash function
C.Message authentication code
D.Block cipher
（73）
A.of
B.for
C.with
D.in
（74）
A.hash
B.stream
C.ciphertext
D.plaintext
（75）
A.collisions
B.image
C.preimage
D.solution
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