We utilize the framework xJsnark to build the circuit for the zero-knowledge proof system in our construction.

Our Contribution

• HashRsaCircuit/blob/master/JsnarkCircuitBuilder/src/examples/generators/rsahash/RSAEncryptionHashCircuitGenerator.java The circuit generation algorithm for our construction.
• HashRsaCircuit/blob/master/JsnarkCircuitBuilder/src/examples/tests/rsahash/HashRSAEncryption_Test.java The unit test of testing the correctness for our implementation.

jsnark

This is a Java library for building circuits for preprocessing zk-SNARKs. The library uses libsnark as a backend (https://github.com/scipr-lab/libsnark), and can integrate circuits produced by the Pinocchio compiler (https://vc.codeplex.com/SourceControl/latest) when needed by the programmer. The code consists of two main parts:

• JsnarkCircuitBuilder: A Java project that has a Gadget library for building/augmenting circuits. (Check the src/examples package)
• libsnark/jsnark_interface: A C++ interface to libsnark which accepts circuits produced by either the circuit builder or by Pinocchio's compiler directly.

Prerequisites

• Libsnark prerequisites
• JDK 8 (Higher versions are also expected to work. We've only tested with JDKs 8 and 12.)
• Junit 4
• BouncyCastle library

For Ubuntu 14.04, the following can be done to install the above:

• To install libsnark prerequisites:

  $ sudo apt-get install build-essential cmake git libgmp3-dev libprocps3-dev python-markdown libboost-all-dev libssl-dev

Note: Don't clone libsnark from https://github.com/scipr-lab/libsnark. Make sure to use the modified libsnark submodule within the jsnark cloned repo in the next section.

• To install JDK 8:

  $ sudo add-apt-repository ppa:webupd8team/java

  $ sudo apt-get update

  $ sudo apt-get install oracle-java8-installer

Verify the installed version by java -version. In case it is not 1.8 or later, try $ sudo update-java-alternatives -s java-8-oracle

• To install Junit4:

  $ sudo apt-get install junit4

• To download BouncyCastle:

  $ wget https://www.bouncycastle.org/download/bcprov-jdk15on-159.jar

Installation Instructions

• Run $ git clone --recursive https://github.com/MengLing-L/HashRsaCircuit.git

• Run:

  $ cd HashRsaCircuit/libsnark

  $ git submodule init && git submodule update

  $ mkdir build && cd build && cmake ..

  $ make

The CMakeLists files were modified to produce the needed executable for the interface. The executable will appear under build/libsnark/jsnark_interface

• Compile and test the JsnarkCircuitBuilder project as in the next section..

Running and Testing JsnarkCircuitBuilder

To compile the JsnarkCircuitBuilder project via command line, from the jsnark directory:

$ cd JsnarkCircuitBuilder
$ mkdir -p bin
$ javac -d bin -cp /usr/share/java/junit4.jar:bcprov-jdk15on-159.jar  $(find ./src/* | grep ".java$")

The classpaths of junit4 and bcprov-jdk15on-159.jar may need to be adapted in case the jars are located elsewhere. The above command assumes that bcprov-jdk15on-159.jar was moved to the JsnarkCircuitBuilder directory.

Before running the following, make sure the PATH_TO_LIBSNARK_EXEC property in config.properties points to the path of the run_ppzksnark executable.

To build the circuit of the zero-knowledge proof system in our construction, the following command can be used

$ java -cp bin:bcprov-jdk15on-159.jar examples.generators.rsahash.RSAEncryptionHashCircuitGenerator

To run one of the JUnit tests available:

$ java -cp bin:/usr/share/java/junit4.jar:bcprov-jdk15on-159.jar org.junit.runner.JUnitCore  examples.tests.rsahash.HashRSAEncryption_Test

Some of the examples and tests will require bcprov-jdk15on-159.jar as well to be added to the classpath.

Note: An IDE, e.g. Eclipse, or possibly the ant tool can be used instead to build and run the Java project more conveniently.

Writing Circuits using jsnark

To summarize the steps needed:

• Extend the CircuitGenerator class.
• Override the buildCircuit() method: Identify the inputs, outputs and prover witness wires of your circuit, and instantiate/connect gadgets inside.
• Override the generateSampleInput() method: Specify how the values of the input and possibly some of the free prover witness wires are set. This helps in quick testing.
• To run a generator, the following methods should be invoked:
  • generateCircuit(): generates the arithmetic circuit and the constraints.
  • evalCircuit(): evaluates the circuit.
  • prepFiles(): This produces two files: <circuit name>.arith and <circuit name>.in. The first file specifies the arithemtic circuit in a way that is similar to how Pinocchio outputs arithmetic circuits, but with other kinds of instructions, like: xor, or, pack and assert. The second file outputs a file containing the values for the input and prover free witness wires. This step must be done after calling evalCircuit() as some witness values are computed during that step.
  • runLibsnark(): This runs the libsnark interface on the two files produced in the last step. By default, this method runs the r1cs_ppzksnark proof system implemented in libsnark. For other options see below.
• Note: In the executing thread, use one CircuitGenerator per thread at a time. If multiple generators are used in parallel, each needs to be in a separate thread, and the corresponding property value in config.properties need to be adapted.

Running circuit outputs on libsnark

Given the .arith and the .in files, it's possible to use command line directly to run the jsnark-libsnark interface. You can use the executable interface run_ppzksnark that appears in jsnark/libsnark/build/libsnark/jsnark_interface to run the libsnark algorithms on the circuit. The executable currently allows to run the proof systems r1cs_ppzksnark (default) and r1cs_gg_ppzksnark implemented in libsnark. To run the first, the executable just takes two arguments: the arithmetic circuit file path, and a sample input file path. To run the r1cs_gg_ppzksnark proof system [Gro16], the first argument should be gg, followed by the arithmetic circuit file path, and the sample input file path.

Running circuits compiled by Pinocchio on libsnark

• To use Pinocchio directly with libsark, run the interface executable run_ppzksnark on the <circuit name>.arith and <circuit name>.in files. The <circuit name>.in should specify the hexadecimal value for each input and nizkinput wire ids, in the following format: id value, each on a separate line.
• It is important to assign 1 to the wire denoted as the one wire input in the arithmetic file.

Disclaimer

The code is undergoing more testing and integration of other features. The future versions of this library will include more documentation, examples and optimizations.

Author

This code is developed and maintained by Ahmed Kosba [email protected]. Please email for any questions.