spdzi

SPDZ, an acronym for "Semi-Honest Privacy and Scalability for Secure Multiparty Computation," is a protocol designed to enable secure multiparty computation (MPC) among multiple parties. MPC is a cryptographic technique that allows multiple parties to jointly compute a function over their private inputs while keeping those inputs private. SPDZ is notable for its efficiency and scalability, making it suitable for practical applications.

The SPDZ protocol was first introduced in a paper by Cramer, Damgård, and Nielsen in 2008. It is based on the concept of secret sharing, where each party's private input is divided into shares distributed among all parties. The protocol ensures that no single party can learn anything about another party's input beyond what can be inferred from the output of the computation.

SPDZ operates in two phases: an offline phase and an online phase. During the offline phase, the parties generate correlated randomness, which is used to preprocess the data. This phase can be done ahead of time and does not require the presence of the actual inputs. The online phase involves the actual computation, where the parties use the preprocessed data to compute the desired function securely.

One of the key features of SPDZ is its ability to handle malicious adversaries, ensuring security even if some parties deviate from the protocol. This is achieved through the use of zero-knowledge proofs and other cryptographic techniques. The protocol also supports a wide range of computational tasks, including arithmetic circuits and some forms of boolean circuits.

SPDZ has been implemented in various software frameworks, making it accessible for researchers and practitioners. Its efficiency and versatility have made it a popular choice for secure multiparty computation in both academic research and real-world applications.