'Loads a PKCS#1.5 PEM-encoded public key file from OpenSSL.
These files can be recognised in that they start with BEGIN PUBLIC KEY
rather than BEGIN RSA PUBLIC KEY.
The contents of the file before the "-----BEGIN PUBLIC KEY-----" and
after the "-----END PUBLIC KEY-----" lines is ignored.
:param keyfile: contents of a PEM-encoded file that contains the public
key, from OpenSSL.
:return: a PublicKey object'

@classmethod
def load_pkcs1_openssl_pem(cls, keyfile):

    der = rsa.pem.load_pem(keyfile, 'PUBLIC    KEY')
    return cls.load_pkcs1_openssl_der(der)
