dodikk/themis-xamarin-prototype

Prototype project which uses themis SecureCell in C# on iOS and android

This repository is experimental and is not supported by cossacklabs, authors of themis

The project depends on themis library binaries. The version has been pinned to v0.13.2.

Other versions can be found in tags and branches

• v0.13.2
• v0.12.0

How to build and run

1. Open app/ThemisDemoXamarin.sln in VisualSturio (either windows or mac)
2. Select ThemisDemoXamarin.iOS or ThemisDemoXamarin.Android with Set as Startup project
3. Build and run
4. Look into console logs.
5. Note: on android search for [themis demo] prefix since the system generates a lot of other logs

Prototype notes:

For convenience the dependencies have been committed into this git repo since it is a prototype and is not supposed to be changed frequently. If you need later versions, please do the following steps:

1. update Cartfile in lib-native/ios directory
2. update java *.aar package links in scripts/download-binaries-droid.sh
3. run configure.sh which will download artefacts from the internet

No windows scripts yet but please feel free to send a pull request.

If you are planning to build your project on top of this prototype

Do not commit binaries and artefacts to your repo

• *.framework ios artefacts
• Carthage directory binary contents
• *.aar packages

Known issues

Build artefact optimizer of Xamarin.Forms or Xamarin.Android might strip native Java classes from the binding lib. This happens when Link SDK assemblies only option is selected for the Linker Behaviour settings entry. See the logs example below.

TL;DR; Add proguard.cfg file to your android app project with the following text:

-keep class com.cossacklabs.themis.**
-keep class com.cossacklabs.themis.** {*;}

Make sure that it has a ProguardConfiguration build step.

The issue could not be reproduced on this demo project yet. However, a larger commercial project had it for the same .cproj settings of both themis bindings and android app project. For example:

Java.Lang.IncompatibleClassChangeError: no non-static method "Lcom/cossacklabs/themis/SecureCellSeal;.decrypt([B[B)[B"
[orion.mobile]   at Java.Interop.JniEnvironment+InstanceMethods.GetMethodID (Java.Interop.JniObjectReference type, System.String name, System.String signature) [0x0005b] in <42d2b7086f0a46efb99253c5db1ecca9>:0 
[orion.mobile]   at Android.Runtime.JNIEnv.GetMethodID (System.IntPtr kls, System.String name, System.String signature) [0x00007] in <3080427739614e60a939a88bf3f838d5>:0 
[orion.mobile]   at Com.Cossacklabs.Themis.SecureCell+ISealInvoker.Decrypt (System.Byte[] p0, System.Byte[] p1) [0x00017] in <cd618986d1ce4194b63cdd3366dad291>:0 
[orion.mobile]   at Themis.Droid.CellSealDroid.UnwrapData (Themis.ISecureCellData cipherTextData, System.Byte[] context) [0x0007e] in <a492e7118e094c3296442a386fe5d80e>:0 
[orion.mobile]    --- End of inner exception stack trace ---

More info can be found in the following github issue of the cossacklabs/themis repository: cossacklabs/themis#716

Useful articles that helped troubleshooting:

• https://gist.github.com/JonDouglas/dda6d8ace7d071b0e8cb
• https://stackoverflow.com/questions/38967851/missing-methods-and-classes-in-jar-after-building-xamarin-app
• https://medium.com/androiddevelopers/troubleshooting-proguard-issues-on-android-bce9de4f8a74
• https://blog.mindorks.com/things-to-care-while-using-proguard-in-android-application
• https://blog.mindorks.com/r8-vs-proguard-in-android
• https://www.jon-douglas.com/2017/04/13/linker-bitdiffer/

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