added XXfallback handshake, getters for local and peer ephemeral (#28)

patterns.go

@@ -98,6 +98,15 @@ var HandshakeXX = HandshakePattern{
 	},
 }
 
+var HandshakeXXfallback = HandshakePattern{
+	Name: "XXfallback",
+	Messages: [][]MessagePattern{
+		{MessagePatternE},
+		{MessagePatternE, MessagePatternDHEE, MessagePatternS, MessagePatternDHSE},
+		{MessagePatternS, MessagePatternDHES},
+	},
+}
+
 var HandshakeIX = HandshakePattern{
 	Name: "IX",
 	Messages: [][]MessagePattern{

state.go

@@ -495,3 +495,16 @@ func (s *HandshakeState) PeerStatic() []byte {
 func (s *HandshakeState) MessageIndex() int {
 	return s.msgIdx
 }
+
+// PeerEphemeral returns the ephemeral key provided by the remote peer during
+// a handshake. It is an error to call this method if a handshake message
+// containing a static key has not been read.
+func (s *HandshakeState) PeerEphemeral() []byte {
+	return s.re
+}
+
+// LocalEphemeral returns the local ephemeral key pair generated during
+// a handshake.
+func (s *HandshakeState) LocalEphemeral() DHKey {
+	return s.e
+}