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Verificatum Multiplicative Groups Library for Java (VMGJ)


This package allows invoking GMP's modular exponentiation, including the extension provided by the GMP Modular Exponentiation Extension package (GMPMEE) for simultaneous or fixed base modular exponentiation and primality testing, from within a Java application. This drastically improves the speed of such operations compared to pure Java implementations.

The following assumes that you are using a release. Developers should also read


The source consists of both Java and C code. The Java source essentially provides a wrapper of the functionality implemented in C on top of GMP using Java Native Interface (JNI).

You also need to build and install the GMPMEE package before building this package. The LIBRARY_PATH must point to and libgmpmee.a and C_INCLUDE_PATH must point to gmp.h and gmpmee.h. This is usually the case automatically after installing GMP and GMPMEE. Then use


to build the library.

If you prefer to use the Clang compiler in place of GCC for the native code, then you may use ./configure CC=clang instead of the above to enable it.

Caution: Please understand that although it seems that Clang works as well as GCC, switching compiler is a large change for mature software.


  1. Use

     make install

    to install the library libvmgj-<VERSION>.{la,a,so} and the jar-file verificatum-vmgj-<VERSION>.jar in the standard locations.

  2. You should also make sure that the newly installed jar-file is found by java by updating your CLASSPATH, e.g., on Ubuntu, you can use something similar to the following snippet in your init script.

     export CLASSPATH=/usr/local/share/java/verificatum-vmgj-<VERSION>.jar:${CLASSPATH}
  3. You need to tell the JVM where your native library, i.e., libvmgj-<VERSION>.{la,a,so} can be found. You may either pass the location using the java.library.path property, e.g.,

     java -Djava.library.path=/usr/local/lib/

    or you can set the shell variable LD_LIBRARY_PATH once and for all in an init file, e.g.,

     export LD_LIBRARY_PATH=/usr/local/lib:${LD_LIBRARY_PATH}
  4. You can test if you managed to build correctly by executing:

     make check

    This runs a set of tests.


You can run a set of benchmarks using

    make bench

Consult to see how these are invoked if you are interested in customizing this for other security parameters.

API Documentation

You may use

    make api

to invoke Javadoc to build the API. The API is not installed anywhere. You can copy it to any location.

Reporting Bugs

Minor bugs should be reported in the repository system as issues or bugs. Security critical bugs, vulnerabilities, etc should be reported directly to the Verificatum Project. We will make best effort to disclose the information in a responsible way before the finder gets proper credit.