密碼學(xué)替代技術(shù)

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

正如我們已經(jīng)討論的那樣， 什么是替代技術(shù)，以及哪種類型的Ceasar Cipher ？ 因此，此處我們不在此討論，請(qǐng)參考密碼學(xué)：CeasarCipher此處： 密碼學(xué)：Caesar Cipher及其Python實(shí)現(xiàn)

替代技術(shù)的類型 (Types of Substitution Techniques)

1. Mono-alphabetic Cipher:

1.單字母密碼：

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.

一旦知道單個(gè)字母的任何鍵替換，Caesar Cipher的可預(yù)測(cè)性就是它的弱點(diǎn)，那么我們就可以解密整個(gè)消息，幾乎需要25次嘗試才能破解它。

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.

在這種技術(shù)中，我們只需將任意隨機(jī)鍵替換為每個(gè)字母即可 ，即可以用B到Z的任何字母替換“ A”，并且可以將“ B”更改為其余字母，但以此類推。 假設(shè)我們用E代替A并不意味著B(niǎo)將被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.

在數(shù)學(xué)上，我們有26個(gè)字母排列，這意味著(26 x 25 x 24 x ... 2)大約有4 x 1026個(gè)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.

它只有一個(gè)問(wèn)題，那就是使用這種技術(shù)創(chuàng)建的短文本，加密分析師可以僅根據(jù)她的英語(yǔ)知識(shí)來(lái)嘗試不同的攻擊。 英國(guó)分析家發(fā)現(xiàn)，字母P出現(xiàn)的概率為13.33％ ，其次是Z ，其出現(xiàn)概率為11.67％ ，而字母C，K，L，N或R的出現(xiàn)概率可以忽略不計(jì)。 密碼分析員可以嘗試使用各種字母代替密文字母，也可以尋找單詞的重復(fù)模式，例如單詞“ to”或“ is”在英語(yǔ)中經(jīng)常出現(xiàn)，因此她可以嘗試替換字母中的所有T和O密文，并進(jìn)一步推論出三個(gè)字母詞，例如“ the” ， “ and”等。

2. Homophonic Substitution Cipher:

2.諧音替代密碼：

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.

諧音取代和單字母取代非常相似。 就像在普通密碼變電站中一樣，我們用一個(gè)鍵替換一個(gè)字母，但是在同音替換的情況下，我們使用一組固定鍵(一個(gè)以上的鍵)映射一個(gè)字母。 例如， A可以替換為H，J，O，P，而B(niǎo)可以替換為以下任意A，但其鍵集為D，I，W，Z等。

3. Polygram Substitution Cipher:

3.多邊形替代密碼：

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替換密碼中，我們沒(méi)有替換一個(gè)純文本字母，而是簡(jiǎn)單地用另一個(gè)單詞塊替換了一個(gè)單詞塊。 例如， “ INCLUDEHELP”將更改為“ WDSAEQTGTAI”，而“ HELP”將替換為“ RYCV” 。 的確是最后四個(gè)字母相同，但兩個(gè)單詞仍然不同。

4. Polyalphabetic Substitution Cipher:

4.多字母替代密碼：

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

多字母替代密碼是萊昂·巴蒂斯塔(Leon Battista)在1568年提出的，其著名的例子是維格涅爾密碼和博福特密碼 。

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.

我們使用多個(gè)單字符密鑰，每個(gè)密鑰加密一個(gè)純文本字符。 這個(gè)第一個(gè)密鑰加密第一個(gè)純文本字符，第二個(gè)密鑰加密第二個(gè)純文本字符，依此類推，畢竟使用了密鑰然后將它們回收。 如果有50個(gè)單字母密鑰，則純文本中的^第 50 ^個(gè)字符將使用相同的密鑰放置，并且該數(shù)字(在我們的示例中為50)是密碼的周期 。

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

多字母變電站密碼的要點(diǎn)如下：

It uses a set of related mono-alphabetic substitution rules.

它使用一組相關(guān)的單字母替換規(guī)則。

The ruleused for transformations determined by the key it uses.

用于轉(zhuǎn)換的規(guī)則，由它使用的鍵確定。

翻譯自: https://www.includehelp.com/cryptography/substitution-techniques.aspx

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