python密码学凯撒密码

Hello everyone, in this tutorial you’ll learn about Caesar cipher in Python. If you have learned about cryptography then you should have known this term Caesar cipher. Well if you don’t know what is this then let me explain it to you.

大家好，在本教程中，您将学习Python中的Caesar密码。 如果您了解密码学，那么您应该知道这个术语凯撒密码。 好吧，如果您不知道这是什么，那么让我向您解释。

What is Caesar Cipher?

什么是凯撒密码？

In cryptography, Caesar cipher is one of the simplest and most widely known encryption techniques. It is also known with other names like Caesar’s cipher, the shift cipher, Caesar’s code or Caesar shift. This encryption technique is used to encrypt plain text, so only the person you want can read it. The method is named after Julius Caesar, who used it in his private correspondence.

在密码术中，凯撒密码是最简单和最广为人知的加密技术之一。 也有其他名称，例如凯撒密码，移位密码，凯撒代码或凯撒移位。 这种加密技术用于加密纯文本，因此只有您想要的人才能阅读它。 该方法以尤利乌斯·凯撒(Julius Caesar)命名，他在私人通讯中使用了该方法。

In this encryption technique, to encrypt our data,  we have to replace each letter in the text by a some other letter at a fixed difference. Let’s say, there is a letter ‘T’ then with a right shift of 1 it will be ‘U’ and with a left shift of 1 it will become ‘S’.  So here, the difference is 1 and the direction will also be same for a text. Either we can use left shift or right, not both in same text.

在这种加密技术中，要加密我们的数据，我们必须以固定的差异将文本中的每个字母替换为另一个字母。 假设有一个字母“ T”，然后向右移1则为“ U”，向左移1则为“ S”。 因此，在这里，差异为1，文本的方向也将相同。 我们可以在同一文本中不使用左移或右移。

Let’s understand it with an easy example.

让我们通过一个简单的例子来理解它。

Example

例

Suppose we have text “the crazy programmer” to be encrypted. Then what we can do is replace each of letter present in the text by a another letter having fixed difference. Lets say we want right shift by 2 then each letter of the above text have to replaced by the letter, positioned second from the letter.

假设我们要加密“疯狂的程序员”文本。 然后，我们可以做的是将文本中出现的每个字母替换为另一个具有固定差异的字母。 假设我们要右移2，则上述文本中的每个字母都必须替换为第二个字母。

Plaintext: the crazy programmer

明文：疯狂的程序员

Ciphertext: vjg etcba rtqitcoogt

密文： vjg etcba rtqitcoogt

Now user can’t  read this text until he/she have the decrypt key.  Decrypt key is nothing just the knowledge about how we shifted those letters while encrypting it. To decrypt this we have to left shift all the letters by 2.

现在，只有拥有解密密钥，用户才能阅读此文本。 解密密钥不只是关于我们在加密时如何移动这些字母的知识。 要解密，我们必须将所有字母左移2。

That was the basic concept of Caesar cipher.  If we see this encryption technique in mathematical way then the formula to get encrypted letter will be:

那就是凯撒密码的基本概念。 如果我们以数学方式看到这种加密技术，那么获得加密字母的公式将是：

c = (x + n) mod 26

c =(x + n)mod 26

where, c is place value of encrypted letter,

其中，c是加密字母的位值，

x is place value of actual letter,

x是实际字母的位置值，

n is the number that shows us how many positions of letters we have to replace.

n是显示我们必须替换多少个字母位置的数字。

On other hand, to decrypt each letter we’ll use the formula given below:

另一方面，要解密每个字母，我们将使用以下公式：

c = (x – n) mod 26

c =(x – n)mod 26

适用于Python的Caesar Cipher程序 (Program for Caesar Cipher in Python)

def encrypt(string, shift):cipher = ''for char in string: if char == ' ':cipher = cipher + charelif  char.isupper():cipher = cipher + chr((ord(char) + shift - 65) % 26 + 65)else:cipher = cipher + chr((ord(char) + shift - 97) % 26 + 97)return ciphertext = input("enter string: ")
s = int(input("enter shift number: "))
print("original string: ", text)
print("after encryption: ", encrypt(text, s))

Output:

输出：

enter string: the crazy programmer enter shift number: 2 original string: the crazy programmer after encryption: vjg etcba rtqitcoogt

输入字符串：疯狂的程序员 输入班次编号：2 原始字符串： 加密后 的疯狂程序员 ：vjg etcba rtqitcoogt

So in above program we have used the same formula (with some modification) we mentioned above. But in computer science ‘A’ is different from ‘a’ thats why we have to write that formula twice, (for uppercase and lowercase letters).

因此，在上面的程序中，我们使用了上面提到的相同公式(进行了一些修改)。 但是在计算机科学中，“ A”与“ a”不同，这就是为什么我们必须两次写该公式(对于大写和小写字母)。

As you can see in the program we have added and subtracted 65 (for Uppercase) and 97 (for lowercase) in that mathematical formula because the ascii value of ‘A’ is 65 and of ‘a’ is 97. The ord() method is used to get the ascii value of the letters.

正如您在程序中所看到的，我们在该数学公式中加减了65(对于大写)和97(对于小写)，因为“ A”的ascii值为65，而“ a”的ascii值为97。ord()方法用于获取字母的ascii值。

Note 1: if you want left shift instead of right then please enter a negative number in ‘enter shift number: ’.

注意1：如果要左移而不是右移，请在“输入移位号：”中输入一个负数。

Note 2: the above program will work only for Python 3.x because input() method works different in both Python 2 and 3. To use the above program in Python 2, use raw_input() in place of input() method.

注意2：上面的程序仅适用于Python 3.x，因为input()方法在Python 2和3中都不同。要在Python 2中使用上面的程序，请使用raw_input()代替input()方法。

To decrypt this message, we will use the same above program but with a small modification.

要解密此消息，我们将使用与上述相同的程序，但进行少量修改。

cipher = cipher + chr((ord(char) – shift – 65) % 26 + 65)

cipher = cipher + chr((ord(char)– shift – 65)％26 + 65 )

If you’ve any problem or suggestion related to caesar cipher in python then please let us know in comments.

如果您对python中的凯撒密码有任何疑问或建议，请在评论中告知我们。

翻译自: https://www.thecrazyprogrammer.com/2018/05/caesar-cipher-in-python.html

python密码学凯撒密码