def recoverPubkey(idText, cert, caPubkey):
<EOL>assertType(cert, ec1Element)<EOL>assertType(caPubkey, ec1Element)<EOL>return _exp(cert, idText)*cert + caPubkey<EOL>
A client can recover the server's pubkey using the identity string @idText,
server's implicit @cert, and the trusted @caPubkey.