Would a RSA encrypted Diffie-Hellman handshake enable secure communication?
I’m encrypting communication from a silverlight client to a php webservice.
The silverlight client initiates they key agreement by sending the RSA public key encrypted DH parameters to the webservice. Only the webservice has the private key, so a MITM attack is not possible. The webservice sends plain text answer back to the client, and a key is agreed upon. This key is then used to encrypt communication between the webservice and silverlight client with AES, which is also encrypted with the RSA public key.
Does anyone see a flaw?
This gains you nothing over just using SSL with a server certificate that’s embedded in the client, and a cipher suite that uses DH key exchange.