Alice and Bob both already know the sym key.

<kadence> Alice generates a RSA keypair, encrypts the public key with the sym key
<kadence> send the encrypted public key to Bob
<kadence> Bob decrpypts it using the sym key
<kadence> generates a session key, encrypts with Alice's public key
<kadence> sends to Alice
<kadence> Alice decrypts message with her private key
<kadence> both now have a session key