extracting public key from certificate and encrypting data

Question

This is for a homework assignment! I get the server's certificate using get_peer_certificate() and the calling dump_certificate to dump the certificate in a variable. The format is PEM and looks right to me.

-----BEGIN CERTIFICATE-----
GIBBERISH................
......................
........................

-----END CERTIFICATE-----

How do I extract the server's public key from this file ('server.pubkey') and encrypt plaintext using RSA algorithm and any python library. At the time of writing this, I am using pyOpenSSL

Answer 1

I'd recommend using a more broad crypto library such as M2Crypto which has the X509 certificate functions as well as RSA encryption:

from M2Crypto import RSA, X509
data = ssl_sock.getpeercert(1)
# load the certificate into M2Crypto to manipulate it
cert = X509.load_cert_string(data, X509.FORMAT_DER)
pub_key = cert.get_pubkey()
rsa_key = pub_key.get_rsa()
cipher = rsa_key.public_encrypt('plaintext', RSA.pkcs1_padding)

Answer 2

    from OpenSSL import crypto        
    crtObj = crypto.load_certificate(crypto.FILETYPE_ASN1, config.x509_certificate)
    pubKeyObject = crtObj.get_pubkey()
    pubKeyString = crypto.dump_publickey(crypto.FILETYPE_PEM, pubKeyObject)