An example of asymmetric encryption in python using a public/private keypair - utilizes RSA from PyCrypto library

RSA_example.py

# Inspired from http://coding4streetcred.com/blog/post/Asymmetric-Encryption-Revisited-(in-PyCrypto)
# PyCrypto docs available at https://www.dlitz.net/software/pycrypto/api/2.6/

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

def generate_keys():
	# RSA modulus length must be a multiple of 256 and >= 1024
	modulus_length = 256*4 # use larger value in production
	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) # base64 encoded strings are database friendly
	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

########## BEGIN ##########

a_message = "The quick brown fox jumped over the lazy dog"
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))

I ran this code but got an error. It is python 3.7 running the latest PyCryptodome
Would you mind helping? I am a little lost...

File "C:(the file location and name but i'm not going to list it).py", line 29
print "%s - (%d)" % (privatekey.exportKey() , len(privatekey.exportKey()))
^
SyntaxError: invalid syntax

@maxharrison These print statements indicate it was written for python 2. It could be easily fixable by making use of the print function instead of the print statement., however, no guarantees.

I am trying to learn this stuff. When I run this, I get the following error.
return (self.key._encrypt(c),) TypeError: argument 1 must be int, not str
I googled and found a bit on b64encode to be imported or encrypt(hash_pass, 32)[0] to include .encode('hex') but to no avail. Can you help?

Hi @anoopsaxena76,

Just change the encryption line as this:
encrypted_msg = encrypt_message(a_message.encode("utf-8"), publickey)

I just did it myself, it works like a charm

I ran this code but got an error. It is python 3.7 running the latest PyCryptodome

Hey, I'm trying to run this code on Python 3.7 too. What did you change apart from that print statement to adapt the code to Pycrytodome?
I get the error:

File "C:/Users/...(don't want to show this bit)/Gavcoin3.py", line 15, in
from crypto.Hash import SHA
File "C:\Users(don't want to show this bit)\AppData\Local\Programs\Python\Python37\lib\site-packages\crypto\Hash\SHA.py", line 24, in
from Crypto.Hash.SHA1 import doc, new, block_size, digest_size
ModuleNotFoundError: No module named 'Crypto'

Please help!

Hi @GavinAren,

I hope you've already solved your issue but if not:
Look in your python directory for /Lib/site-packages/crypto and change it to Crypto. (Capital C)

I ran this code but got an error. It is python 3.7 running the latest PyCryptodome

Hey, I'm trying to run this code on Python 3.7 too. What did you change apart from that print statement to adapt the code to Pycrytodome?
I get the error:

File "C:/Users/...(don't want to show this bit)/Gavcoin3.py", line 15, in
from crypto.Hash import SHA
File "C:\Users(don't want to show this bit)\AppData\Local\Programs\Python\Python37\lib\site-packages\crypto\Hash\SHA.py", line 24, in
from Crypto.Hash.SHA1 import doc, new, block_size, digest_size
ModuleNotFoundError: No module named 'Crypto'

Please help!

PyCrypto is written and tested using Python version 2.1 through 3.3. Python
1.5.2 is not supported. My POC resolves that pycrypto is obsoleted in python3.7. Pycryptodome is working alternative of it, but unfortunately it doesn't support plain RSA cryptography.

    def encrypt(self, plaintext, K):
        raise NotImplementedError("Use module Crypto.Cipher.PKCS1_OAEP instead")