Create a self signed X509 certificate in Python

Here is how to create a self signed certificate in Python using OpenSSL:

from OpenSSL import crypto, SSL
from socket import gethostname
from pprint import pprint
from time import gmtime, mktime

CERT_FILE = "selfsigned.crt"
KEY_FILE = "private.key"

def create_self_signed_cert():
            
        # create a key pair
        k = crypto.PKey()
        k.generate_key(crypto.TYPE_RSA, 1024)

        # create a self-signed cert
        cert = crypto.X509()
        cert.get_subject().C = "UK"
        cert.get_subject().ST = "London"
        cert.get_subject().L = "London"
        cert.get_subject().O = "Dummy Company Ltd"
        cert.get_subject().OU = "Dummy Company Ltd"
        cert.get_subject().CN = gethostname()
        cert.set_serial_number(1000)
        cert.gmtime_adj_notBefore(0)
        cert.gmtime_adj_notAfter(10*365*24*60*60)
        cert.set_issuer(cert.get_subject())
        cert.set_pubkey(k)
        cert.sign(k, 'sha1')

        open(CERT_FILE, "wt").write(
            crypto.dump_certificate(crypto.FILETYPE_PEM, cert))
        open(KEY_FILE, "wt").write(
            crypto.dump_privatekey(crypto.FILETYPE_PEM, k))

create_self_signed_cert()

You can then use m2crypto library to encrypt and decrypt data using this self signed certificate. You use public key to encrypt and private key to decrypt:

f = open(CERT_FILE)
cert_buffer = f.read()
f.close()

from M2Crypto import RSA, X509 
cert = X509.load_cert_string(cert_buffer, X509.FORMAT_PEM) 
pub_key = cert.get_pubkey() 
rsa_key = pub_key.get_rsa() 
cipher = rsa_key.public_encrypt('plaintext', RSA.pkcs1_padding)

print cipher

ReadRSA = RSA.load_key(KEY_FILE)
try:
    plaintext = ReadRSA.private_decrypt (cipher, RSA.pkcs1_padding)
except:
    print "Error: wrong key?"
    plaintext = ""

print plaintext