Support for the MIT GSS-API library is now available for the Android platform – complete with an org.ietf.jgss (RFC 5653) compatible application programming interface, wolfSSL cryptography integration, and NDK sample application.
You may have read our previous blog entry announcing the initial phases of our effort to port the MIT Kerberos libraries and wolfSSL embedded SSL library to the Android platform (see link in Reference section, below). This post described initial availability of the Kerberos libraries to Android through the native NDK framework – enabling Android NDK developers to add Kerberos support to their NDK applications at a native C or C++ programming level. At that time, we also commented on next steps for the project and sought feedback from the community on adding a Java API to make using Kerberos on Android easier and more standardized.
Since that time, we have been hard at work enhancing the project, adding support for a new Java GSS-API wrapper, updating our example code, and adding new features to our sample NDK application.
1. Java GSS-API Wrapper
The addition of a Java wrapper around the native MIT GSS-API took part in two stages – a SWIG-generated (http://www.swig.org/) Java interface, which then in turn was used as a building block for a org.ietf.jgss Java API. The individual layers are visualized in the figure below. Both the SWIG layer and the Java GSS-API layer are able to be used in a Java application to access the underlying MIT Kerberos/GSS-API libraries. The SWIG layer is more tedious to use and less standardized than the Java GSS-API layer, but is closer to the C programming API of the native MIT GSS-API. We suggest that Java developers use the org.ietf.jgss Java interface over using the SWIG layer directly. As the org.ietf.jgss interface followed RFC 5653, Java developers should be able to refer to the standard Java documentation for the org.ietf.jgss package for usage instructions and class descriptions.
Source code for this project has been released under the open source MIT license, and is currently available for download on GitHub. Both the Java Generic Security Services API wrappers (SWIG and Java GSS-API), as well as example client and server applications and build instructions are located in the kerberos-java-gssapi package, at the following GitHub URL:
2. Enhanced Example Code
Included in the Java GSS-API package, we have created several example applications to help developers understand how to use this project in their own application. There are two sets of client and server examples provided. The first one is a set of client and server applications which directly use the SWIG-generated Java interface. The second set of applications is a client and server that use the more standardized Java GSS-API interface (org.ietf.jgss).
It is recommended for Java developers to use the Java GSS-API examples, as they demonstrate programming and API usage which is more common in the Java programming language. Before running any of the included examples, the development machine must first have a krb5.conf file and KDC set up correctly to match the principal names used in the examples. For more details about building and running these example applications, please see the README included in the kerberos-java-gssapi package.
3. Sample NDK Application
As one of the main goals of this project was to bring MIT Kerberos/GSS-API support to the Android platform, we have created a sample Android NDK application to serve as an example and reference to Android developers. This sample application provides a GUI wrapper around the MIT Kerberos kinit, klist, kvno, and kdestroy applications. It also provides a sample client using the Java GSS-API interface to connect and communicate with the example server application (from Section 2, above).
This package contains cross-compiled version of the MIT Kerberos libraries, and includes instructions on how to re-compile the Kerberos libraries yourself for the Android platform. For details on how to build and run this example application in the Android emulator, please see the README file located in the NDK application package.
All sources for this sample application are located in the kerberos-android-ndk package, located at the following URL:
yaSSL and MIT are excited to bring Android developers MIT Kerberos and GSS-API support and look forward to seeing what kinds of applications will use this functionality. If you have any questions, comments, or feedback, we would enjoy to hear it! Please contact us directly at firstname.lastname@example.org.
MIT Kerberos: http://web.mit.edu/kerberos/
Initial announcement: https://www.wolfssl.com/android-kerberos-port-using-wolfssl-embedded-ssl/