Python Encryption Cipher

by jamied_uk 15th June 2016, 02:17

Python Encryption Cipher

Usage python python_vigenere_cipher.py textfile.txt key123

Code:: #!/usr/bin/env python # # Usage python python_vigenere_cipher.py e (or d) textfile.txt key123 # # # How it works: Let the two users be denoted sender (S) and receiver (R). # S and R send each other messages in the form of plaintext (.txt) files. # S passes R a .txt file encrypted using this program, and R must decrypt # it using this program. Therefore, only those in possession of this program # will be able to read the encrypted messages. # The program uses the Vigenere cipher for encyrption and decryption, a cipher # which requires a keyword. Thus, S and R must not only share this program, # but they must also have common knowledge of the keyword. import os import sys if len(sys.argv) < 2: os.system('clear') print "Usage Example: python python_vigenere_cipher.py e (or d) textfile.txt key123" exit() def encrypt(textfile, key): '''Encrypts a textfile using the Vigenere cipher with given keyword. For example, encrypt('goo.txt', 'key') creates an encrypted file named 'goo_encoded.txt' using the Vignere cipher with keyword 'key'. After encryption is complete, deletes original file''' plaintext = open(textfile, 'r') ciphertext = open(textfile.strip('.txt') + '_encrypted.txt', 'w') msg = plaintext.read() listChars = [] listKey = [] EncListChars = [] EncMsg = '' keylist = list(key + '^*&') for char in msg: listChars.append(ord(char)-32) for i in range(len(msg)): listKey.append(ord(keylist[i % len(keylist)])-32) for i in range(len(msg)): EncListChars.append((listChars[i] + listKey[i]) % 96) for i in range(len(msg)): EncMsg += chr(EncListChars[i] + 32) ciphertext.write(EncMsg) plaintext.close() ciphertext.close() os.remove(textfile) def decrypt(textfile, key): '''Decrypts an encoded textfile using the Vigenere cipher with given keyword.''' ciphertext = open(textfile, 'r') plaintext = open(textfile.replace('_encrypted', ''), 'w') EncMsg = ciphertext.read() EncListChars = [] listKey = [] listChars = [] msg = '' keylist = list(key + '^*&') for char in EncMsg: EncListChars.append(ord(char)-32) for i in range(len(EncMsg)): listKey.append(ord(keylist[i % len(keylist)])-32) for i in range(len(EncMsg)): listChars.append((EncListChars[i] - listKey[i]) % 96) for i in range(len(EncMsg)): msg += chr(listChars[i] + 32) plaintext.write(msg) plaintext.close() ciphertext.close() if __name__ == '__main__': if sys.argv[1] == 'e': encrypt(sys.argv[2], sys.argv[3]) if sys.argv[1] == 'd': decrypt(sys.argv[2], sys.argv[3]) if sys.argv[1] == 'help': print 'Usage:' print 'Encryption: python encryptor.py e plaintext.txt keyword' print 'Decryption: python encryptor.py d ciphertext.txt keyword'