[tinydtls-dev] ChangeCipherSpec and client_key_exchange problem

[Priyanka <priyanka206@xxxxxxxxx>]

Hi,

I am testing tinydtls latest version from eclipse as Contiki application.
However, I do not have a complete handshake between a tinydtls server and client.

Server manages to find FOUND PEER but then it lose the peer as it is not able to interpret client_key_exchange sent by the client.

Debug messages show that SERVER prints "expected ChangeCipherSpec during handshake" whereas CLIENT keeps re-transmitting client_key_exchange (16) to the server.

Sometimes there is no crash but sometimes either the server or the client crashes after FOUND PEER and then if I restart the server or client to see if handshake gets complete, I have sequence no mismatch problem ( wrong epoch etc).
I found that this problem could arise when  ChangeCipherSpec message from server arrives out of order before client_key_exchange (16) is sent to the server. It was stated that cipher spec message should be stored in buffer before client key exchange could be sent.

Any idea how can I resolve this issue? I am testing only PSK.

SERVER 

dtls_handle_message: FOUND PEER

got packet 20 (14 bytes)

DEBG receive header: (13 bytes):

00000000 14 FE FD 00 00 00 00 00  00 00 06 00 01

DEBG receive unencrypted: (1 bytes):

00000000 01

expected ChangeCipherSpec during handshake

In udp_send

event timer!

node=0

node type:0, epoch:0, length:0

now:7978, node->t:0, node:0

now:7978 node:0

CLIENT 

In udp_found

found peer, try to re-connect

Client received message from aaaa::200:2f3c:c6b5:3:20220

dtls_handle_message: FOUND PEER

got packet 22 (25 bytes)

DEBG receive header: (13 bytes):

00000000 16 FE FD 00 00 00 00 00  00 00 04 00 0C

DEBG receive unencrypted: (12 bytes):

00000000 0E 00 00 00 00 02 00 00  00 00 00 00

received handshake packet of type: server_hello_done (14)

handle handshake packet of type: server_hello_done (14)

DEBG add MAC data: (12 bytes): 0E0000000002000000000000

DEBG add MAC data: (12 bytes): 100000110002000000000011

DEBG add MAC data: (17 bytes): 000F436C69656E745F6964656E74697479

send handshake packet of type: client_key_exchange (16)

Thanks

Priyanka