1  # liboprf
 2  
 3  ## Overview
 4  
 5  liboprf is a library for Oblivious Pseudorandom Functions (OPRFs), including support for Threshold OPRFs. It is designed to make advanced cryptographic protocols easy to integrate across applications.
 6  
 7  ## What is an OPRF?
 8  
 9  An Oblivious Pseudorandom Function (OPRF) is a two-party cryptographic primitive involving a sender and receiver who jointly compute a function, `F`, in such a way that:
10  - The sender holds a secret key `k`
11  - The receiver provides an input `x`
12  - The receiver learns `F(k, x)` but nothing about `k`
13  - The sender learns nothing about `x` or `F(k, x)`
14  
15  OPRFs are the foundation for many privacy-preserving protocols including:
16  - Password-based authentication without exposing passwords
17  - Private set intersection, which allows two parties to find the intersection of their private sets without revealing the full sets
18  - Privacy-preserving information retrieval, allowing users to get specific information from a database without revealing what information is being retrieved
19  
20  ## Features
21  
22  ### Basic OPRF
23  liboprf implements the basic OPRF(ristretto255, SHA-512) variant from the [IRTF CFRG Draft](https://github.com/cfrg/draft-irtf-cfrg-voprf/), "Oblivious Pseudorandom Functions (OPRFs) using Prime-Order Groups".
24  
25  ### Threshold OPRF
26  liboprf implements a threshold OPRF variant based on [Krawczyk et al. (2017)](https://eprint.iacr.org/2017/363) which is compatible with the [CFRG OPRF(ristretto255, SHA-512) variant](#basic-oprf). A threshold implementation distributes trust among multiple servers, requiring a minimum number (threshold) to cooperate for operation. It uses Distributed Key Generation (DKG) protocols, as described below, to distribute secret key shares among multiple servers. 
27  
28  ### 3hashTDH
29  This library also implements the 3hashTDH from [Gu, Jarecki, Kedzior, Nazarian, Xu (2024)](https://eprint.iacr.org/2024/1455) "Threshold PAKE with Security against Compromise of all Servers". This implementation is compatible with the aforementioned [IRTF CFRG OPRF(ristretto255, SHA-512)](#basic-oprf) variant.
30  
31  ### Distributed Key Generation (DKG)
32  For the [threshold OPRF](#threshold-oprf), liboprf provides:
33  
34  - **Trusted Party DKG**: An implementation based on Joint Feldman DKG (JF-DKG) from the paper "[Secure Distributed Key Generation for Discrete-Log Based Cryptosystems](https://link.springer.com/article/10.1007/s00145-006-0347-3)" by R. Gennaro, S. Jarecki, Hugo Krawczyk & T. Rabin.
35  
36  - **Semi-trusted DKG**: Implements Fast-Track Joint Verifiable Secret Sharing (FT-Joint-DL-VSS) described in R. Gennaro, M. O. Rabin, and T. Rabin, "[Simplified VSS and fast-track multiparty computations with applications to threshold cryptography](https://dl.acm.org/doi/10.1145/277697.277716)" In B. A. Coan and Y. Afek, editors, 17th ACM PODC, pages 101–111. ACM, June/July 1998.
37  
38  ### Threshold OPRF Updates
39  To update a threshold OPRF instantiation, liboprf contains multi-party multiplication described in R. Gennaro, M. O. Rabin, and T. Rabin, "[Simplified VSS and fast-track multiparty computations with applications to threshold cryptography](https://dl.acm.org/doi/10.1145/277697.277716)" In B. A. Coan and Y. Afek, editors, 17th ACM PODC, pages 101–111. ACM, June/July 1998.
40  
41  ## Installation
42  
43  ### Dependencies
44  - **libsodium**: You must install [libsodium](https://github.com/jedisct1/libsodium) first. libsodium is a cryptographic library that provides a range of cryptographic operations including encryption, decryption, digital signatures, and secure password hashing.
45  - **pkgconf**: Needed for building the library.
46  
47  ### Building from source
48  
49  ```bash
50  git clone https://github.com/stef/liboprf.git
51  cd liboprf/src
52  make
53  sudo make install
54  ```
55  
56  ### Python Wrapper
57  A Python wrapper, `pyoprf`, is provided. Look at [its README](/python/README.md) for installation and usage instructions. 
58  
59  
60  ## Funding
61  
62  This project is funded through [NGI0 Entrust](https://nlnet.nl/entrust), a fund
63  established by [NLnet](https://nlnet.nl) with financial support from the
64  European Commission's [Next Generation Internet](https://ngi.eu) program. Learn
65  more at the [NLnet project page](https://nlnet.nl/project/ThresholdOPRF).
66  
67  [<img src="https://nlnet.nl/logo/banner.png" alt="NLnet foundation logo" width="20%" />](https://nlnet.nl)
68  [<img src="https://nlnet.nl/image/logos/NGI0_tag.svg" alt="NGI Zero Logo" width="20%" />](https://nlnet.nl/entrust)