2016年下半年信息安全工程师上午综合知识解析：

71-75（1）is thescience of hiding information. Whereas the goal of cryptography is to make dataunreadable by a third party. the goal of steganography（[ˌstegə'nɒgrəfɪ]隐写术） is to hide the data from a third party. In this article, I willdiscuss what steganography is, what purposes it serves, and will provide anexample using available software.

Thereare a large number of steganographic （2）that most ofus are familiar with (especially if you watch a lot of spy movies), rangingfrom invisible ink and microdots to secreting a hidden message in the second letterof each word of a large body of text and spread spectrum radio communication.With computers and networks, there are many other ways of hiding informations,such as:

Covertchannels (c,g, Loki and some distributed denial-of-service tools use theInternet Control （3）Protocol, or ICMP, as the communication channel between the “bad guy”and acompromicyed system)

Hiddentext within Web pages

Hidingfiles in “plain sight”(c,g. what better place to “hide”a file thanwith an important sounding name in the c:\winnt system32 directory)

Nullciphers(c,g, using the first letter of each word to form a hidden message in anotherwise innocuous text)

steganographytoday, however, is significantly more （4）than theexample about suggest, allowing a user to hide large amounts of informationwithin image and audio. These forms of steganography often are used inconjunction with cryptography so the information is double protected; first itis encrypted and then hidden so that an advertisement first. find theinformation ( an often difficult task in and of itself) and the decrypted it.

Thesimplest approach to hiding data within an image file is called （5）signatureinsertion. In this method, we can take the binary representation of the hiddendata and the bit of each byte within the covert image. If we are using 24-bitcolor the amount and will be minimum and indiscriminate to the human eye.

（1）A、Cryptography

B、Geography

C、Stenography

D、Steganography

（2）A、methods

B、software

C、tools

D、services

（3）A、Member

B、Management

C、Message

D、Mail

（4）A、powerful

B、sophistication（[səˌfɪstɪˈkeɪʃn]可理解为先进）

C、advanced

D、easy

（5）A、least（LSB：least significant bit）

B、most

C、much

D、less

信管网解析：

LSB隐写

· LSB全称least significant bit，最低有效位

· PNG文件中的图像像数一般是由RGB三原色（红绿蓝）组成，每一种颜色占用8位，取值范围为0x00~0xFF，即有256种颜色，一共包含了256的3次方的颜色，即16777216 种颜色

· 人类的眼睛可以区分约1000万种不同的颜色

· 这意味着人类的眼睛无法区分余下的颜色大约有6777216种

· LSB隐写就是修改RGB颜色分量的最低二进制位（LSB），而人类的眼睛不会注意到这前后的变化

· 每个像数可以携带3比特的信息

信管网参考答案：A、A、C、B、A