70、在 DES 算法中，需要进行 16 轮加密，每一轮的子密钥长度为（） A、16 B、32 C、48 D、64 解析：
des 算法中，64 位密钥经过置换选择 1、循环左移、置换选择 2 等变换，产生 16 个 48 位长的子密钥。
参考答案：C
71-75（1）is the science of hiding information. Whereas the goal of
cryptography is to make data unreadable by a third party. the goal of steganography（[? steg?'n? gr?f? ]隐写术） is to hide the data from a third party. In this article, I will discuss what steganography is, what purposes it serves, and will provide an example using available software.
There are a large number of steganographic（2）that most of us are familiar with (especially if you watch a lot of spy movies), ranging from invisible ink and microdots to secreting a hidden message in the second letter of 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:
Covert channels (c,g, Loki and some distributed denial-of-service tools use the Internet Control （3）Protocol, or ICMP, as the communication channel between the “bad guy”and a compromicyed system)
Hidden text within Web pages
Hiding files in “plain sight”(c,g. what better place to “hide”a file than with an important sounding name in the c:\\winnt system32 directory)
Null ciphers(c,g, using the first letter of each word to form a hidden message in an otherwise innocuous text) steganography today, however, is significantly more （4）than the example about suggest, allowing a user to
hide large amounts of information within image and audio. These forms of steganography often are used in conjunction with cryptography so the information is double protected; first it is encrypted and then hidden so that an advertisement first. find the information ( an often difficult task in and of itself) and the decrypted it.
The simplest approach to hiding data within an image file is called（5）signature insertion. In this method, we can take the binary representation of the hidden data and the bit of each byte within the covert image. If we are using 24-bit color the amount and will be minimum and indiscriminate to the human eye.
A、Cryptography B、Geography C、Stenography D、Steganography A、methods B、software C、tools D、services
A、Member B、Management C、Message D、Mail
A、powerful
B、sophistication（[s?? f? st? ? ke? ? n]可理解为先进） C、advanced D、easy
A、least（LSB：least significant bit） B、most C、much D、less 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
1000 万种不同的颜色
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
参考答案：A、A、C、B、A
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