Code Review Request, JDK-8167680, DTLS implementation bugs

Xuelei Fan at
Thu Oct 13 14:36:58 UTC 2016


Please review the fix for JDK-8167680:

There are a few implementation bugs in JDK.

1. The sequence number is increased by 2 for GCM cipher suites.
Both GCM crypto operation and DTLS record use the sequence number.  The 
current implementation may increase the sequence number for each of the 
two operations.  It is not the expected behavior.

2. The implementation does not response to handshake retransmissions.
In the current implementation, receiving of retransmitted handshake 
messages does not kick off a retransmission of the previous delivered 
flight.  Retransmission happens on timeout.  Timeout is expensive. 
Supporting response to peer retransmitted handshake messages would speed 
up the handshaking.

3. the final CCC and finished message cannot be retransmitted.
It is an implementation bug.  Every handshake message should be able to 
get retransmitted.

4. the first application data may be discarded if the last flight get lost.
Applications may send application data immediately after the handshake 
completed.  However, the peer may have not receive the handshake 
complete message, and therefor discard the application data.  As may 
impact application logic.

For example

     Client                 Server
        -- ClientKeyExchange -->
        -- ChangeCipherSpec  -->
        -- Finished          -->

        X <-- ChangeCipherSpec --
        X <-- Finished         --

        <-- Application Data  --

        -----    ...        --->
        -- ClientKeyExchange -->
        -- ChangeCipherSpec  -->
        -- Finished          -->

        <-- ChangeCipherSpec --
        <-- Finished         --

1. (omit the previous handshake messages) server sends ChangeCipherSpec 
and Finished messages.
2. server handshake complete
3. server send application
4. client does not receive the ChangeCipherSpec or Finished messages.
5. client receives the application data.  Client cannot handle the 
encrypted message, and may discard it.  Client re-transmit the previous 
6. server retransmit the last flight.
7. client receives the last flight.

In this update, the last flight will be transmit twice.  As may mitigate 
the impact of the issue.

5. resuming handshaking need no cookie exchange.
It is an implementation bug.  Cookie exchange is performed for 
handshaking resuming now.  It is not the expected behavior.

6. need more debug log for DTLS handshake message fragmentation and 


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