Do I have to keep encryption keys on record?

I have an application that will allow secure chat between 2 users using AES (or other) encryption of the messages. To initiate the exchange I will be sending the private key securely through my server. Am I legally obligated to retain a copy of the private key on my server for any reason? I would like for the key to only reside in ram and be unrecoverable overwritten after the exchange.