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（）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（）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which have been designated cryptography standards by the US government(though DES's designation was finally withdrawn after the AES was adopted).Despite its deprecation as an official standard,DES(especially its still-approved and much more secure triple-DES variant)remains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（）the plaintext bit-by-bit or character-by-character,somewhat like the one-time pad.In a stream cipher,the output（）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,（）(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.
问题1选项
A.plaintext
B.ciphertext
C.data
D.hash
问题2选项
A.stream cipher
B.hash function
C.Message authentication code
D.Block cipher
问题3选项
A.of
B.for
C.with
D.in
问题4选项
A.hash
B.stream
C.ciphertext
D.plaintext
问题5选项
A.collisions
B.image
C.preimage
D.solution
在几种不同类型的软件维护中，通常情况下（）所占工作量最大。
在()中，项目经理的权力是最小的。
在项目实施的过程中，项目经理通过项目周报中的项目进度分析图表发现机房施工进度有延期风险。项目经理立即组织相关人员进行分析，下达了关于改进措施的书面指令。该指令属于（ ）
The IT service manager resigns from a project that meets the scheduleand budget. After hiring an alternativenew manager, the team is opposed to the comments from the new manager. The team is at （） developmentstages。
（）is closet to Deming's definition of Quality。
The IT service manager has learned that a software canimprove the efficiency of current and future project tasks. Because the software is fresh to the Company. Theengineer is not familiar with the software. The lT service manager decides to send the highest level engineero attend the external training course. The proiect manager uses （） risk strategies。
The process control charts are used （）。
