| [cf-dev] expected behavior for handshake failure ? |
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Hi, I made some tests[1] with Leshan to check the behavoir of a DTLS handshake failure. Currently when the server is not able to continue the handshake (handshake_failure (40), bad_certificate(42), unsupported_certificate(43), ...) it terminates the session quietly. The client will never get a response, and will retry again an again, this looks like that : -------(test with bad psk)----------- C: Client Hello S: Hello Verify Request C: Client Hello S: Server Hello, Server Hello Done C: Client Key Exhange, Change Cipher Spec, Encrypted Handshake message. // server does not validate the key and close the session quietly // the client try to re-send, and we start a dialogue of deaf ... C: Client Key Exhange, Change Cipher Spec, Encrypted Handshake message. S: Client Hello C: Client Hello C: Client Hello S: Server Hello, Server Hello Done C: Client Key Exhange, Change Cipher Spec, Encrypted Handshake message. C: Client Key Exhange, Change Cipher Spec, Encrypted Handshake message. S: Client Hello .... ... ------------------------------------ I don't know if this is the expected behavior. The TLS 1.2 spec define handshake alert[2] and the Scandium code seems to use it (AlertDescription.class[3]) I find in the code something which should be a bug in terminateConnection[4], we send an alert message only if we have a session in the session store but in case of Handshake failure we have no session in the store (we add it in the store only when the handshake is done) I made a crappy workarround to send the alert message with the session used by the Handshaker and get this : -----(test with bad psk + 1 workaround)-- C: Client Hello S: Hello Verify Request C: Client Hello S: Server Hello, Server Hello Done C: Client Key Exhange, Change Cipher Spec, Encrypted Handshake message. S: Alert (internal error) // server get the error and send an alert // the client ignore it and another kind of dialogue of deaf starts ... C: Client Key Exhange, Change Cipher Spec, Encrypted Handshake message. S: Client Hello S: Client Hello C: Client Hello S: Alert (Unexpected Message) C: Client Key Exhange, Change Cipher Spec, Encrypted Handshake message. S: Client Hello .... ... ------------------------------------ I think we get the same kind of problem at client side when it receives the alert. This time it's in the processAlertRecord[5] method. So, I made the same kind of workaround at client side, the communication looks better but the client still retry again and again until timed out : -----(test with bad psk + 2 workarounds)-- C: Client Hello S: Hello Verify Request C: Client Hello S: Server Hello, Server Hello Done C: Client Key Exhange, Change Cipher Spec, Encrypted Handshake message. S: Alert (internal error) // server get the error and send an alert // client get it, but retry from beginning C: Client Hello S: Hello Verify Request C: Client Hello S: Server Hello, Server Hello Done C: Client Key Exhange, Change Cipher Spec, Encrypted Handshake message. S: Alert (internal error) .... ... ------------------------------------ For a Leshan/Californium user point of view this is a bit strange. When we send a request through DTLS and the handshake fails, we get no feedback and the request just failed with a timeout. Should we get a message reject instead [6] or something like that ? Simon [1]https://github.com/eclipse/leshan/blob/x509-cert-impl/leshan-integration-tests/src/test/java/org/eclipse/leshan/integration/tests/SecurityTest.java#L66 [2]https://tools.ietf.org/html/rfc5246#appendix-A.3 [3]https://github.com/eclipse/californium.scandium/blob/master/src/main/java/org/eclipse/californium/scandium/dtls/AlertMessage.java#L108 [4]https://github.com/eclipse/californium.scandium/blob/master/src/main/java/org/eclipse/californium/scandium/DTLSConnector.java#L417 [5]https://github.com/eclipse/californium.scandium/blob/master/src/main/java/org/eclipse/californium/scandium/DTLSConnector.java#L482 [6]https://github.com/eclipse/californium/blob/master/californium-core/src/main/java/org/eclipse/californium/core/coap/MessageObserver.java#L69 |