'Loads a key in PKCS#1 DER format.
@param keyfile: contents of a DER-encoded file that contains the public
key.
@return: a PublicKey object
First let\'s construct a DER encoded key:
>>> import base64
>>> b64der = \'MAwCBQCNGmYtAgMBAAE=\'
>>> der = base64.decodestring(b64der)
This loads the file:
>>> PublicKey._load_pkcs1_der(der)
PublicKey(2367317549, 65537)'

@classmethod
def _load_pkcs1_der(cls, keyfile):

    from pyasn1.codec.der import decoder
    (priv, _) = decoder.decode(keyfile)
    as_ints = tuple((int(x) for x in priv))
    return cls(*as_ints)
