Multiparty computation with SPDZ, MASCOT, and Overdrive offline phases
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Dragos Rotaru
Dragos Rotaru fixed external io bug
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README.md

(C) 2018 University of Bristol. See License.txt

Software for the SPDZ, MASCOT, and Overdrive secure multi-party computation protocols. See Programs/Source/ for some example MPC programs, and tutorial.md for a basic tutorial.

See also https://www.cs.bris.ac.uk/Research/CryptographySecurity/SPDZ

Preface:

If you are mainly looking to run complete secure computation modulo a prime, SCALE-MAMBA, which is a fork of this software, might be a better fit for you. The software in this repository is better suited to run the online phase (including for $GF(2^n)$) and various offline phases individually.

The software contains some functionality for benchmarking that breaks security. This is deactivated by default. See the compilation section on how to activate it if needed.

In particular, the online phase will discard preprocessed data and crash when it runs out if not in benchmarking mode. In benchmarking mode, it will reuse preprocessed data.

Requirements:

  • GCC (tested with 7.2) or LLVM (tested with 3.8)
  • MPIR library, compiled with C++ support (use flag --enable-cxx when running configure)
  • libsodium library, tested against 1.0.11
  • CPU supporting AES-NI and PCLMUL
  • Python 2.x, ideally with gmpy package (for testing)
  • NTL library for the SPDZ-2 and Overdrive offline phases (optional; tested with NTL 9.10)
  • If using macOS, Sierra or later

To compile SPDZ:

  1. Edit CONFIG or CONFIG.mine to your needs:
  • To benchmark only the online phase (skipping the secure offline phase), add the following line at the top: MY_CFLAGS = -DINSECURE
  • PREP_DIR should point to should be a local, unversioned directory to store preprocessing data (default is Player-Data in the current directory).
  • For the SPDZ-2 and Overdrive offline phases, set USE_NTL = 1 and MOD = -DMAX_MOD_SZ=6.
  • For the MASCOT offline phase or to use GF(2^128) in the online phase, set USE_GF2N_LONG = 1.
  • For processors without AVX (e.g., Intel Atom) or for optimization, set ARCH = -march=<architecture>.
  1. Run make (use the flag -j for faster compilation multiple threads). Remember to run make clean first after changing CONFIG or CONFIG.mine.

To setup for benchmarking the online phase

This requires the INSECURE flag to be set before compilation as explained above. For a secure offline phase, see the section on SPDZ-2 below.

Run:

Scripts/setup-online.sh

This sets up parameters for the online phase for 2 parties with a 128-bit prime field and 40-bit binary field, and creates fake offline data (multiplication triples etc.) for these parameters.

Parameters can be customised by running

Scripts/setup-online.sh <nparties> <nbitsp> <nbits2>

To compile a program

To compile the program in ./Programs/Source/tutorial.mpc, run:

./compile.py tutorial

This creates the bytecode and schedule files in Programs/Bytecode/ and Programs/Schedules/

To run a program

To run the above program (on one machine), first run:

./Server.x 2 5000 &

(or replace 5000 with your desired port number)

Then run both parties' online phase:

./Player-Online.x -pn 5000 0 tutorial

./Player-Online.x -pn 5000 1 tutorial (in a separate terminal)

Or, you can use a script to do the above automatically:

Scripts/run-online.sh tutorial

To run a program on two different machines, firstly the preprocessing data must be copied across to the second machine (or shared using sshfs), and secondly, Player-Online.x needs to be passed the machine where Server.x is running. e.g. if this machine is name diffie on the local network:

./Player-Online.x -pn 5000 -h diffie 0 test_all

./Player-Online.x -pn 5000 -h diffie 1 test_all

Compiling and running programs from external directories

Programs can also be edited, compiled and run from any directory with the above basic structure. So for a source file in ./Programs/Source/, all SPDZ scripts must be run from ./. The setup-online.sh script must also be run from ./ to create the relevant data. For example:

spdz$ cd ../
$ mkdir myprogs
$ cd myprogs
$ mkdir -p Programs/Source
$ vi Programs/Source/test.mpc
$ ../spdz/compile.py test.mpc
$ ls Programs/
Bytecode  Public-Input  Schedules  Source
$ ../spdz/Scripts/setup-online.sh
$ ls
Player-Data Programs
$ ../spdz/Scripts/run-online.sh test

SPDZ-2 offline phase

This implementation is suitable to generate the preprocessed data used in the online phase.

For quick run on one machine, you can call the following:

./spdz2-offline.x -p 0 & ./spdz2-offline.x -p 1

More generally, run the following on every machine:

./spdz2-offline.x -p <number of party> -N <total number of parties> -h <hostname of party 0> -c <covert security parameter>

The number of parties are counted from 0. As seen in the quick example, you can omit the total number of parties if it is 2 and the hostname if all parties run on the same machine. Invoke ./spdz2-offline.x for more explanation on the options.

./spdz2-offline.x provides covert security according to some parameter c (at least 2). A malicious adversary will get caught with probability 1-1/c. There is a linear correlation between c and the running time, that is, running with 2c takes twice as long as running with c. The default for c is 10.

The program will generate every kind of randomness required by the online phase until you stop it. You can shut it down gracefully pressing Ctrl-c (or sending the interrupt signal SIGINT), but only after an initial phase, the end of which is marked by the output Starting to produce gf2n. Note that the initial phase has been reported to take up to an hour. Furthermore, 3 GB of RAM are required per party.

Benchmarking the MASCOT offline phase

The MASCOT implementation is not suitable to generate the preprocessed data for the online phase because it can only generate either multiplication triples or bits. Nevertheless, an online computation only using data of one kind can run from the output of MASCOT offline phase if Player-Online.x is run with the options -lg2 128 -lgp 128.

In order to compile the MASCOT code, the following must be set in CONFIG or CONFIG.mine:

USE_GF2N_LONG = 1

It also requires SimpleOT:

git submodule update --init SimpleOT
cd SimpleOT
make

If SPDZ has been built before, any compiled code needs to be removed:

make clean

HOSTS must contain the hostnames or IPs of the players, see HOSTS.example for an example.

Then, MASCOT can be run as follows:

host1:$ ./ot-offline.x -p 0 -c

host2:$ ./ot-offline.x -p 1 -c

Benchmarking Overdrive offline phases

We have implemented several protocols to measure the maximal throughput for the Overdrive paper. As for MASCOT, these implementations are not suited to generate data for the online phase because they only generate one type at a time.

Binary Protocol
simple-offline.x SPDZ-1 and High Gear (with command-line argument -g)
pairwise-offline.x Low Gear
cnc-offline.x SPDZ-2 with malicious security (covert security with command-line argument -c)

These programs can be run similarly to spdz2-offline.x, for example:

host1:$ ./simple-offline.x -p 0 -h host1

host2:$ ./simple-offline.x -p 1 -h host1

Running any program without arguments describes all command-line arguments.