an example of symmetric encryption in python using a single known secret key - utilizes AES from PyCrypto library

AES_example.py

# Inspired from https://pythonprogramming.net/encryption-and-decryption-in-python-code-example-with-explanation/
# PyCrypto docs available at https://www.dlitz.net/software/pycrypto/api/2.6/

from Crypto.Cipher import AES
import base64, os

def generate_secret_key_for_AES_cipher():
	# AES key length must be either 16, 24, or 32 bytes long
	AES_key_length = 16 # use larger value in production
	# generate a random secret key with the decided key length
	# this secret key will be used to create AES cipher for encryption/decryption
	secret_key = os.urandom(AES_key_length)
	# encode this secret key for storing safely in database
	encoded_secret_key = base64.b64encode(secret_key)
	return encoded_secret_key

def encrypt_message(private_msg, encoded_secret_key, padding_character):
	# decode the encoded secret key
	secret_key = base64.b64decode(encoded_secret_key)
	# use the decoded secret key to create a AES cipher
	cipher = AES.new(secret_key)
	# pad the private_msg
	# because AES encryption requires the length of the msg to be a multiple of 16
	padded_private_msg = private_msg + (padding_character * ((16-len(private_msg)) % 16))
	# use the cipher to encrypt the padded message
	encrypted_msg = cipher.encrypt(padded_private_msg)
	# encode the encrypted msg for storing safely in the database
	encoded_encrypted_msg = base64.b64encode(encrypted_msg)
	# return encoded encrypted message
	return encoded_encrypted_msg

def decrypt_message(encoded_encrypted_msg, encoded_secret_key, padding_character):
	# decode the encoded encrypted message and encoded secret key
	secret_key = base64.b64decode(encoded_secret_key)
	encrypted_msg = base64.b64decode(encoded_encrypted_msg)
	# use the decoded secret key to create a AES cipher
	cipher = AES.new(secret_key)
	# use the cipher to decrypt the encrypted message
	decrypted_msg = cipher.decrypt(encrypted_msg)
	# unpad the encrypted message
	unpadded_private_msg = decrypted_msg.rstrip(padding_character)
	# return a decrypted original private message
	return unpadded_private_msg


####### BEGIN HERE #######


private_msg = """
 Lorem ipsum dolor sit amet, malis recteque posidonium ea sit, te vis meliore verterem. Duis movet comprehensam eam ex, te mea possim luptatum gloriatur. Modus summo epicuri eu nec. Ex placerat complectitur eos.
"""
padding_character = "{"

secret_key = generate_secret_key_for_AES_cipher()
encrypted_msg = encrypt_message(private_msg, secret_key, padding_character)
decrypted_msg = decrypt_message(encrypted_msg, secret_key, padding_character)

print "   Secret Key: %s - (%d)" % (secret_key, len(secret_key))
print "Encrypted Msg: %s - (%d)" % (encrypted_msg, len(encrypted_msg))
print "Decrypted Msg: %s - (%d)" % (decrypted_msg, len(decrypted_msg))