question: private byte [ ] receivedClientKeyExchange ( PSKClientKeyExchange message ) throws HandshakeException { clientKeyExchange = message ; String identity = message . getIdentity ( ) ; byte [ ] psk = pskStore . getKey ( identity ) ; LOGGER . log ( Level . FINER , "Client [{0}] uses PSK identity [{1}]" , new Object [ ] { getPeerAddress ( ) , identity } ) ; if ( psk == null ) { throw new HandshakeException ( String . format ( "Cannot authenticate client, identity [%s] is unknown" , identity ) , new AlertMessage ( AlertLevel . FATAL , AlertDescription . HANDSHAKE_FAILURE , session . getPeer ( ) ) ) ; } session . setPeerIdentity ( new PreSharedKeyIdentity ( identity ) ) ; return generatePremasterSecretFromPSK ( psk ) ; }
target:  Retrieves the preshared key from the identity hint and then generates the premaster secret.