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A fast, portable, and easy to use Oblivious Transfer Library

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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]
  • Several malicious secure batched 1-out-of-2 base OTs from [MRR21]


This library provides several different classes of OT protocols. First is the base OT protocol of [NP01, CO15, MR19, MRR21]. 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. See The

folder for examples.

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.


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 three optional dependencies on libsodium, Relic, or SimplestOT (Unix only) for Base OTs. CMake 3.15+ is required and the build script assumes python 3.

The library can be built as

git clone --recursive
cd libOTe
python --setup --boost --relic
The main executable with examples is
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.

Build Options

LibOTe can be built with various only the selected protocols enabled.

will enable all available protocols depending on platform/dependancies. The
options include

Malicious base OT: *

the SimplestOT [CO15] protocol (relic or sodium). *
the SimplestOT base OT protocol [CO15] protocol (linux assembly). *
the McQuoid Rosulek Roy [MRR20] protocol (relic or sodium). *
the McQuoid Rosulek Roy [MRR21] protocol (sodium fork). *
the Masny Rindal [MR19] protocol (relic or sodium). *
the Masny Rindal [MR19] protocol (Kyber fork). *
the Naor Pinkas [NP01] base OT (relic or sodium).

1-out-of-2 OT Extension: *

the Ishai et al [IKNP03] semi-honest protocol. *
the Keller et al [KOS15] malicious protocol. *
the Burra et al [BLNNOOSS15],[KOS15] malicious Delta-OT protocol. *
the Couteau et al [CRR21],[BCGIKRS19] semi-honest/malicious protocol.

Vole: *

the Couteau et al [CRR21] semi-honest/malicious protocol.

Addiition options can be set for cryptoTools. See the cmake output.


Dependancies can be managed via the
script or or installed via an external tool. If an external tool is used install to system location or set
-D CMAKE_PREFIX_PATH=path/to/install

Boost The library requires boost and can be fetched as

python --setup --boost

Enabling/Disabling Relic (for base OTs): The library can be built with Relic as

python --setup --relic
python -- -D ENABLE_RELIC=ON
Relic can be disabled by removing
from the setup and setting

Enabling/Disabling libsodium (for base OTs): The library can be built with libsodium as

python --setup --sodium
libsodium can be disabled by removing
from the setup and setting
. The McQuoid Rosulek Roy 2021 Base OTs uses a twisted curve which additionally require the
option for Montgomery curves and is currently only in a fork of libsodium. If you prefer the stable libsodium, then install it and add
as a cmake argument to libOTe.


libOTe can be installed and linked the same way as other cmake projects. By default the dependancies are not installed. To install all dependancies, run the following

python --setup --boost --relic --sodium --install
You can also selectively install the dependancies. The install location can be specifying as
. Otherwise the system default is used.

The main library is similarly installed as

python --install 

By default, sudo is not used. If installation requires sudo access, then add

to the
script arguments. See
python --help
for full details.


libOTe can be linked via cmake as

find_package(libOTe REQUIRED)
target_link_libraries(myProject oc::libOTe)
Other exposed targets are
oc::cryptoTools, oc::tests_cryptoTools, oc::libOTe_Tests
. In addition, cmake variables
will be defined, where
is one of the libOTe options.

To ensure that cmake can find libOTe, you can either install libOTe or build it locally and set

or provide its location as a cmake
, i.e.
find_package(libOTe HINTS path/to/libOTe)

Example Code

A minimal working example showing how to perform

OTs using the IKNP protocol. ```cpp 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<:array>> sendMessages(n); sendMessages[0] = { toBlock(54), toBlock(33) }; //...

// Send the messages. sender.sendChosen(sendMessages, prng, senderChl); recverThread.join(); </:array>

} ```


Contact Peter Rindal [email protected] for any assistance on building or running the library.


Spread the word!

    author = {Peter Rindal},
    title = {{libOTe: an efficient, portable, and easy to use Oblivious Transfer Library}},
    howpublished = {\url{}},

## License

This project has been placed in the public domain and/or MIT license. 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.

## 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/~ | ~ | ~ | ~ | ~ |


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

[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

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