Cryptography With Python 简明教程

Symmetric and Asymmetric Cryptography

在本章中，让我们详细讨论对称和非对称密码术。

In this chapter, let us discuss in detail about symmetric and asymmetric cryptography.

Symmetric Cryptography

在此类型中，加密和解密过程使用相同的密钥。它也被称为 secret key cryptography 。对称密码术的主要功能如下：

In this type, the encryption and decryption process uses the same key. It is also called as secret key cryptography. The main features of symmetric cryptography are as follows −

  1. It is simpler and faster.

  2. The two parties exchange the key in a secure way.

Drawback

对称密码术的主要缺点是，如果密钥泄漏给入侵者，则消息可以被轻松地更改，这被视为风险因素。

The major drawback of symmetric cryptography is that if the key is leaked to the intruder, the message can be easily changed and this is considered as a risk factor.

Data Encryption Standard (DES)

最流行的对称密钥算法是数据加密标准 (DES)，且 Python 包含一个软件包，该软件包包括 DES 算法背后的逻辑。

The most popular symmetric key algorithm is Data Encryption Standard (DES) and Python includes a package which includes the logic behind DES algorithm.

Installation

Python 中安装 DES 包 pyDES 的命令为：

The command for installation of DES package pyDES in Python is −

pip install pyDES
pydes

DES 算法的简单程序实现如下：

Simple program implementation of DES algorithm is as follows −

import pyDes

data = "DES Algorithm Implementation"
k = pyDes.des("DESCRYPT", pyDes.CBC, "\0\0\0\0\0\0\0\0", pad=None, padmode=pyDes.PAD_PKCS5)
d = k.encrypt(data)

print "Encrypted: %r" % d
print "Decrypted: %r" % k.decrypt(d)
assert k.decrypt(d) == data

它调用变量 padmode ，它获取所有 DES 算法实现所需的包，并以特定方式执行加密和解密。

It calls for the variable padmode which fetches all the packages as per DES algorithm implementation and follows encryption and decryption in a specified manner.

Output

以下为上述代码运行后的输出：

You can see the following output as a result of the code given above −

des algorithm

Asymmetric Cryptography

它也被称为 public key cryptography. 。它的工作方式与对称加密相反。这意味着它需要两个密钥：一个用于加密，另一个用于解密。公钥用于加密，而私钥用于解密。

It is also called as public key cryptography. It works in the reverse way of symmetric cryptography. This implies that it requires two keys: one for encryption and other for decryption. The public key is used for encrypting and the private key is used for decrypting.

Drawback

  1. Due to its key length, it contributes lower encryption speed.

  2. Key management is crucial.

以下 Python 程序代码演示了如何使用 RSA 算法和实现执行非对称加密：

The following program code in Python illustrates the working of asymmetric cryptography using RSA algorithm and its implementation −

from Crypto import Random
from Crypto.PublicKey import RSA
import base64

def generate_keys():
   # key length must be a multiple of 256 and >= 1024
   modulus_length = 256*4
   privatekey = RSA.generate(modulus_length, Random.new().read)
   publickey = privatekey.publickey()
   return privatekey, publickey

def encrypt_message(a_message , publickey):
   encrypted_msg = publickey.encrypt(a_message, 32)[0]
   encoded_encrypted_msg = base64.b64encode(encrypted_msg)
   return encoded_encrypted_msg

def decrypt_message(encoded_encrypted_msg, privatekey):
   decoded_encrypted_msg = base64.b64decode(encoded_encrypted_msg)
   decoded_decrypted_msg = privatekey.decrypt(decoded_encrypted_msg)
   return decoded_decrypted_msg

a_message = "This is the illustration of RSA algorithm of asymmetric cryptography"
privatekey , publickey = generate_keys()
encrypted_msg = encrypt_message(a_message , publickey)
decrypted_msg = decrypt_message(encrypted_msg, privatekey)

print "%s - (%d)" % (privatekey.exportKey() , len(privatekey.exportKey()))
print "%s - (%d)" % (publickey.exportKey() , len(publickey.exportKey()))
print " Original content: %s - (%d)" % (a_message, len(a_message))
print "Encrypted message: %s - (%d)" % (encrypted_msg, len(encrypted_msg))
print "Decrypted message: %s - (%d)" % (decrypted_msg, len(decrypted_msg))

Output

当您执行上述代码时，可以找到以下输出：

You can find the following output when you execute the code given above −

rsa