I'm trying to do key exchange using the following scheme.

  1. Server generates an RSA-2048 key pair and sends the public part to the client
  2. Client generates an RSA-592 key pair (I have to use RSA-592 due to client performance reasons; 592 bits is the minimum key size for encrypting 256 bits using OAEP)
  3. Client encrypts the public part of the key pair using the public key from the server, and sends it to the server
  4. Server encrypts AES-256 key (random) using the client's RSA key pair, and sends it to the client

So, is this secure than plain RSA-592?

  • You only need to provide the public key to the client, likewise you only need to send the server the public key for the client.
    – RoraΖ
    Sep 15, 2014 at 12:40

1 Answer 1


Your scheme is not secure as you're sending the private key of the server over the wire (in your first step).

Extension (after update of question)

The scheme is still not secure as now I can intercept the public key from the server and replace it with my own certificate (Man-in-the-Middle-Attack).

To secure your scheme you have to use a CA (even you can create your own CA for this).

  • If I use CA, is this more secure than plain RSA-592 with CA? Sep 20, 2014 at 8:58

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