A fast and portable C++17 library for Oblivious Transfer extension (OTe). The primary design goal of this library to obtain high performance while being easy to use. This library currently implements:

• The semi-honest 1-out-of-2 OT [IKNP03].
• The semi-honest 1-out-of-2 Silent OT [BCGIKRS19].
• The semi-honest 1-out-of-2 Delta-OT [IKNP03],[BLNNOOSS15].
• The semi-honest 1-out-of-N OT [KKRT16].
• The malicious secure 1-out-of-2 OT [KOS15].
• The malicious secure 1-out-of-2 Delta-OT [KOS15],[BLNNOOSS15].
• The malicious secure 1-out-of-N OT [OOS16].
• The malicious secure approximate K-out-of-N OT [RR16].
• The malicious secure 1-out-of-2 base OT [NP01].
• The malicious secure 1-out-of-2 base OT [CO15] (Faster Linux ASM version disabled by default).
• The malicious secure 1-out-of-2 base OT [MR19]

Introduction

This library provides several different classes of OT protocols. First is the base OT protocol of [NP01, CO15, MR19]. These protocol bootstraps all the other OT extension protocols. Within the OT extension protocols, we have 1-out-of-2, 1-out-of-N and K-out-of-N, both in the semi-honest and malicious settings.

All implementations are highly optimized using fast SSE instructions and vectorization to obtain optimal performance both in the single and multi-threaded setting. See the Performance section for a comparison between protocols and to other libraries.

Networking can be performed using both the sockets provided by the library and external socket classes. See the networking tutorial for an example.

Example Code

A minimal working example showing how to perform n OTs using the IKNP protocol.

void minimal()
{
    // Setup networking. See cryptoTools\frontend_cryptoTools\Tutorials\Network.cpp
    IOService ios;
    Channel senderChl = Session(ios, "localhost:1212", SessionMode::Server).addChannel();
    Channel recverChl = Session(ios, "localhost:1212", SessionMode::Client).addChannel();

    // The number of OTs.
    int n = 100;

    // The code to be run by the OT receiver.
    auto recverThread = std::thread([&]() {
        PRNG prng(sysRandomSeed());
        IknpOtExtReceiver recver;

        // Choose which messages should be received.
        BitVector choices(n);
        choices[0] = 1;
        //...

        // Receive the messages
        std::vector<block> messages(n);
        recver.receiveChosen(choices, messages, prng, recverChl);

        // messages[i] = sendMessages[i][choices[i]];
    });

    PRNG prng(sysRandomSeed());
    IknpOtExtSender sender;

    // Choose which messages should be sent.
    std::vector<std::array<block, 2>> sendMessages(n);
    sendMessages[0] = { toBlock(54), toBlock(33) };
    //...

    // Send the messages.
    sender.sendChosen(sendMessages, prng, senderChl);
    recverThread.join();
}

Performance

The running time in seconds for computing n=2²⁴ OTs on a single Intel Xeon server (2 36-cores Intel Xeon CPU E5-2699 v3 @ 2.30GHz and 256GB of RAM) as of 11/16/2016. All timings shown reflect a "single" thread per party, with the expection that network IO in libOTe is performed in the background by a separate thread.

Type	Security	Protocol	libOTe (SHA1/AES)	Encrypto Group (SHA256)	Apricot (AES-hash)	OOS16 (blake2)	emp-toolkit (AES-hash)
1-out-of-N (N=276)	malicious	OOS16	10.6 / 9.2	~	~	24**	~
1-out-of-N (N=2128)	passive	KKRT16	9.2 / 6.7	~	~	~	~
1-out-of-2 Delta-OT	malicious	KOS15	1.9*	~	~	~	~
1-out-of-2 Delta-OT	passive	KOS15	1.7*	~	~	~	~
1-out-of-2	malicious	ALSZ15	~	17.3	~	~	10
1-out-of-2	malicious	KOS15	3.9 / 0.7	~	1.1	~	2.9
1-out-of-2	passive	IKNP03	3.7 / 0.6	11.3	0.6	~	2.7
1-out-of-2 Base	malicious	CO15	1,592/~	~	~	~	~
1-out-of-2 Base	malicious	NP00	12,876/~	~	~	~	~

Build

The library is cross platform and has been tested on Windows, Mac and Linux. There is one mandatory dependency on Boost 1.75 (networking), and optional dependency on Relic. CMake and Python 3 are also required to build and visual studio 2019 is assumed on windows.

git clone --recursive https://github.com/osu-crypto/libOTe.git
cd libOTe
python build.py setup boost relic
python build.py -DENABLE_RELIC=ON -DENABLE_ALL_OT=ON

It is possible to build only the protocol(s) that are desired via cmake command. In addition, if boost and or relic are already installed, then boost or relic can be ommitted from python build.py setup boost relic.

See the output of python build.py or cmake . for available compile options. For example,

python build.py -DENABLE_IKNP=ON

will only build the [iknp04] protocol.

The main executable with examples is frontend and is located in the build directory, eg out/build/linux/frontend/frontend.exe, out/build/x64-Release/frontend/Release/frontend.exe depending on the OS.

Enabling/Disabling Relic (for base OTs):

• Relic can be disabled by using the build commands

python build.py setup boost
python build.py -DENABLE_IKNP=ON

This will disable many/all of the supported base OT protocols. In addition, you will need to manually enable the specific protocols you desire, eg as above.

Installing libOTe is only partially supported.

Linking

The helper scripts cmake/loadCacheCar.cmake, cmake/libOTeHeler.cmake can be used to find all dependencies when not installing libOTe. See libPSI for an example. In addition, the libOTe build script/cmake will output many of the dependency while the remaining will be located in the build directory.

Help

Contact Peter Rindal peterrindal@gmail.com for any assistance on building or running the library.

Citing

Spread the word!

@misc{libOTe,
    author = {Peter Rindal},
    title = {{libOTe: an efficient, portable, and easy to use Oblivious Transfer Library}},
    howpublished = {\url{https://github.com/osu-crypto/libOTe}},
}

License

This project has been placed in the public domain. As such, you are unrestricted in how you use it, commercial or otherwise. However, no warranty of fitness is provided. If you found this project helpful, feel free to spread the word and cite us.

Citation

[IKNP03] - Yuval Ishai and Joe Kilian and Kobbi Nissim and Erez Petrank, Extending Oblivious Transfers Efficiently.

[KOS15] - Marcel Keller and Emmanuela Orsini and Peter Scholl, Actively Secure OT Extension with Optimal Overhead. eprint/2015/546

[OOS16] - Michele Orrù and Emmanuela Orsini and Peter Scholl, Actively Secure 1-out-of-N OT Extension with Application to Private Set Intersection. eprint/2016/933

[KKRT16] - Vladimir Kolesnikov and Ranjit Kumaresan and Mike Rosulek and Ni Trieu, Efficient Batched Oblivious PRF with Applications to Private Set Intersection. eprint/2016/799

[RR16] - Peter Rindal and Mike Rosulek, Improved Private Set Intersection against Malicious Adversaries. eprint/2016/746

[BLNNOOSS15] - Sai Sheshank Burra and Enrique Larraia and Jesper Buus Nielsen and Peter Sebastian Nordholt and Claudio Orlandi and Emmanuela Orsini and Peter Scholl and Nigel P. Smart, High Performance Multi-Party Computation for Binary Circuits Based on Oblivious Transfer. eprint/2015/472

[ALSZ15] - Gilad Asharov and Yehuda Lindell and Thomas Schneider and Michael Zohner, More Efficient Oblivious Transfer Extensions with Security for Malicious Adversaries. eprint/2015/061

[NP01] - Moni Naor, Benny Pinkas, Efficient Oblivious Transfer Protocols.