Integrate Signal-Encryption plugin

[tassadarius]

About

Students at FH-Hagenberg started a project to visualize the Signal-Ecryption algorithm. The code has been lying around some time so finish and integrate it.

TODOs

• [x] finalize descriptions
• [x] Create basic online help
• [ ] Create basic context help
• [x] Create English translation
• [x] Clean-up code to minimum acceptable level

Bugs

• [x] Recreating only one key leads to error

   I suspect it uses the wrong one-time key and is then confused

• [ ] Sometimes when going back and forth a value is missing in the capturer

   I could narrow it down that if you switch state somewhat randomly 
   (probably there is a pattern) a value is missing when switching to bob sending

  java.lang.NullPointerException: Cannot invoke "org.whispersystems.libsignal.ecc.ECPublicKey.serialize()" because "this.sendingCapture.publicDiffieHellmanRatchetKey" is null
  at org.jcryptool.visual.signalencryption.communication.MessageContext.diffieHellmanSenderPublicKey(MessageContext.java:154)
  at org.jcryptool.visual.signalencryption.ui.DoubleRatchetBobSendingLogic.updateSendingKeyDisplayInformation(DoubleRatchetBobSendingLogic.java:490)
  at org.jcryptool.visual.signalencryption.ui.DoubleRatchetBobSendingLogic$BobSendingStep$2.switchState(DoubleRatchetBobSendingLogic.java:63)
  at org.jcryptool.visual.signalencryption.ui.DoubleRatchetStep.next(DoubleRatchetStep.java:21)
  at org.jcryptool.visual.signalencryption.ui.DoubleRatchetAliceSendingLogic.stepForward(DoubleRatchetAliceSendingLogic.java:505)
  at org.jcryptool.visual.signalencryption.ui.DoubleRatchetView.lambda$3(DoubleRatchetView.java:179)
  at org.jcryptool.visual.signalencryption.util.UiUtils$1.widgetSelected(UiUtils.java:100)
  at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:252)
  at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:89)
  at org.eclipse.swt.widgets.Display.sendEvent(Display.java:5745)
  at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1427)
  at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:5013)
  at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:4507)

• [x] Small layout problems (especially with those expanders 😠)

Optional improvements

• [ ] Create good online help
• [ ] Create good context help
• [x] Refactor code to improve readability

[tassadarius]

I would say we can close this. If there are no Mac/Windows problems it's production ready IMHO

[simlei]

What a great plugin 👌