In this chapter, let us discuss in detail about symmetric and asymmetric cryptography.
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 −
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.
The most popular symmetric key algorithm is Data Encryption Standard (DES) and Python includes a package which includes the logic behind DES algorithm.
The command for installation of DES package pyDES in Python is −
pip install pyDES
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
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.
You can see the following output as a result of the code given above −
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.
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) 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))
You can find the following output when you execute the code given above −