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which have been designated cryptography standards by the US government(though DES's designation was finally withdrawn after the AES was adopted).Despite its deprecation as an official standard,DES(especially its still-approved and much more secure triple-DES variant)remains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
一台主机的IP地址为202.123.25.36，掩码为255.255.254.0。如果该主机需要在该网络进行直接广播，那么它应该使用的目的地址为（ ）
在计算机系统的日常维护工作中，应当注意硬盘工作时不能__(2)__。另外，需要防范病毒，而__(3)__是不会被病毒感觉的。
有 4 个 IP 地址：201.117.15.254、201.117.17.01、201.117.24.5 和 201.117.29.3，如果子网掩码为 255.255.248.0，则这 4 个地址分别属于3个子网；其中属于同一个子网的是（）
在异步通信中，每个字符包含1位起始位、7位数据位、1位奇偶位和1位终止位，每秒钟传送200个字符，采用4相位调制，则码元速率为（）。
在 Windows 中，运行（ ）命令得到下图所示结果。以下关于该结果的叙述中，错误的是（ ）。
Pinging 59.74.111.8 with 32 bytes of data:
Reply from 59.74.111.8: bytes=32 time=3ms TTL=60
Reply from 59.74.111.8: bytes=32 time=5ms TTL=60
Reply from 59.74.111.8: bytes=32 time=3ms TTL=60
Reply from 59.74.111.8: bytes=32 time=5ms TTL=60
Ping statistics for 59.74.111.8:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 3ms, Maximum = 5ms, Average = 4ms
在ISO OSF/RM参考模型中，七层协议中的__(1)__利用通信子网提供的服务实现两个用户进程之间端到端的通信。在这个模型中，如果A用户需要通过网络向B用户传送数据，则首先将数据送入应用层，在该层给它附加控制信息后送入表示层；在表示层对数据进行必要的变换并加头标后送入会话层；在会话层加头标送入传输层；在传输层将数据分解为__(本题)__后送至网络层；在网络层将数据封装成__(3)__后送至数据链路层；在数据链路层将数据加上头标和尾标封装成__(4)__后发送到物理层；在物理层数据以__(5)__形式发送到物理线路。B用户所在的系统接收到数据后，层层剥去控制信息，把原数据传送给B用户。
在OSI/RM中，解释应用数据语义的协议层是（）。
在TCP/IP协议栈中，ARP协议的作用是（）,RARP协议的作用是（请作答此空）。
在地址 http://www.dailynews.com.cn/channel/welcome.htm 中，www.dailynews.com.cn 表示（ ），welcome.htm 表示（请作答此空）。
在电子表格软件Excel中，假设A1单元格的值为15，若在A2单元格输入“=AND(15＜A1，A1＜100)”，则A2单元格显示的值为 （）
