密码学替代技术_替代技术及其类型| 密码学

密码学替代技术

As we already discussed what are the Substitution techniques and one of its type Ceasar Cipher? So we are not discussing it here for that please refer to Cryptography: CeasarCipher here: Cryptography: Caesar Cipher and its Python Implementations

正如我们已经讨论的那样， 什么是替代技术，以及哪种类型的Ceasar Cipher ？因此，此处我们不在此讨论，请参考密码学：CeasarCipher此处： 密码学：Caesar Cipher及其Python实现

替代技术的类型 (Types of Substitution Techniques)

1. Mono-alphabetic Cipher:

1.单字母密码：

Predictability of Caesar Cipher was its weakness once any key replacement of a single alphabet is known then, the whole message can we decipher and almost 25 attempts are required to break it.

一旦知道单个字母的任何键替换，Caesar Cipher的可预测性就是它的弱点，那么我们就可以解密整个消息，几乎需要25次尝试才能破解它。

In this technique, we simply substitute any random key for each alphabet letter, that is 'A' can be being replaced with any letters from B to Z and 'B' can be changed to rest of the Alphabets but itself and so on. Let's say we substitute A with E that doesn't mean that B will be replaced by F.

在这种技术中，我们只需将任意随机键替换为每个字母即可 ，即可以用B到Z的任何字母替换“ A”，并且可以将“ B”更改为其余字母，但以此类推。假设我们用E代替A并不意味着B将被F取代 。

Mathematically, we have 26 alphabet permutation which means (26 x 25 x 24 x...2) which is about 4 x 1026 possibilities.

在数学上，我们有26个字母排列，这意味着(26 x 25 x 24 x ... 2)大约有4 x 1026个可能性。

There is only one problem with it and that is short text created using this technique, a crypto analyst can try different attacks solely based on her knowledge of the English language. English analyst found that the probability of occurrence of the letter P is 13.33% which highest followed by Z with 11.67% and occurrence of letters like C, K, L, N or R is negligible. A cryptanalyst can try various alphabets in place of cipher-text alphabet or she can look for repeated patterns of the word for is example word 'to' or 'is' occur frequently in English so she can try replacing all the T's and O's from the cipher-text and deduce further to three letter words like 'the', 'and' and so on.

它只有一个问题，那就是使用这种技术创建的短文本，加密分析师可以仅根据她的英语知识来尝试不同的攻击。英国分析家发现，字母P出现的概率为13.33％ ，其次是Z ，其出现概率为11.67％ ，而字母C，K，L，N或R的出现概率可以忽略不计。密码分析员可以尝试使用各种字母代替密文字母，也可以寻找单词的重复模式，例如单词“ to”或“ is”在英语中经常出现，因此她可以尝试替换字母中的所有T和O密文，并进一步推论出三个字母词，例如“ the” ， “ and”等。

2. Homophonic Substitution Cipher:

2.谐音替代密码：

The Homophonic substitution and mono-alphabetic substitution are very much alike. Like in plain cipher substation we replace an alphabet with a key but in case of Homophonic Substitution, we map an alphabet with a set of fixed keys (more than one key). For instance, A can be replaced with H, J, O, P and B will replace with any of the following inspite of A's key set D, I, W, Z etc.

谐音取代和单字母取代非常相似。就像在普通密码变电站中一样，我们用一个键替换一个字母，但是在同音替换的情况下，我们使用一组固定键(一个以上的键)映射一个字母。例如， A可以替换为H，J，O，P，而B可以替换为以下任意A，但其键集为D，I，W，Z等。

3. Polygram Substitution Cipher:

3.多边形替代密码：

In Polygram substitution cipher, instead of replacing one plain-text alphabet we simply replace a block of the word with another block of a word. Example, 'INCLUDEHELP' will change to 'WDSAEQTGTAI' whereas 'HELP' will replace to 'RYCV'. This is true that the last four letters are the same but still different in both words.

在Polygram替换密码中，我们没有替换一个纯文本字母，而是简单地用另一个单词块替换了一个单词块。例如， “ INCLUDEHELP”将更改为“ WDSAEQTGTAI”，而“ HELP”将替换为“ RYCV” 。的确是最后四个字母相同，但两个单词仍然不同。

4. Polyalphabetic Substitution Cipher:

4.多字母替代密码：

Polyalphabetic Substitution cipher was introduced by Leon Battista in the year 1568, and its prominent examples are Vigenère cipher and Beaufort cipher.

多字母替代密码是莱昂·巴蒂斯塔(Leon Battista)在1568年提出的，其著名的例子是维格涅尔密码和博福特密码 。

We use multiple one-character keys, each key encrypts one plain-text character. This first key encrypts the first plain-text character, the second the key encrypt the second plain-text character and so on, after all, keys are used then they are recycled. If 50 one-letter keys, every 50^th character in the plain text would be placed with the same key and this number (in our case, 50) is period of the cipher.

我们使用多个单字符密钥，每个密钥加密一个纯文本字符。这个第一个密钥加密第一个纯文本字符，第二个密钥加密第二个纯文本字符，依此类推，毕竟使用了密钥然后将它们回收。如果有50个单字母密钥，则纯文本中的^第 50 ^个字符将使用相同的密钥放置，并且该数字(在我们的示例中为50)是密码的周期 。

The key points of the polyalphabetic substation cipher are the following:

多字母变电站密码的要点如下：

It uses a set of related mono-alphabetic substitution rules.
它使用一组相关的单字母替换规则。
The ruleused for transformations determined by the key it uses.
用于转换的规则，由它使用的键确定。