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Nillion’s MPC Protocol

Nillion’s novel MPC protocol extends the capabilities of Linear Secret-Sharing Schemes (LSSS) to perform some non-linear operations, specifically evaluating a sum of products of non-zero user inputs.

The protocol workflow is split into 2 phases:

Phase 1: Pre-processing to create shares

The pre-processing phase prepares for the network to securely handle the high value data so that future computations can be performed without revealing individual inputs.

The point of pre-processing is to generate and distribute shares (masks) for each factor and term in the sum of products expression using standard MPC techniques.

Pre-processing is independent of input values. This phase only depends on the number of inputs (factors and terms) so that the appropriate number of shares are created ahead of computation.

Phase 2: Non-Interactive computation on masked factors

The computation phase is where the actual calculations on the private inputs are performed. Computation can be broken into 3 stages: input, evaluation, and output.

Input Stage

Shares generated during the pre-processing phase are distributed to parties. A party receives one share per input. Parties combine their inputs with shares to create masked factors. These multiplicatively homomorphic masked factors are broadcasted to the network, maintaining information-theoretic security (ITS).

Evaluation Stage

The evaluation stage utilizes the computationally homomorphic properties of the masked factors, enabling operations like addition and multiplication to be carried out directly on the masked data.

Parties perform local calculations on masked factors.

Output Stage

Parties reveal the result of local calculations. These results are aggregated to derive and output the final result of the multi-party computation.

Protocol Features

Nillion’s novel MPC protocol achieves

  • Non-linear arithmetic capabilities: The protocol can evaluate a sum of products of hidden inputs without leaking input information to any of the parties.
  • Efficient pre-processing: The creation of shares is independent of input values and only depends on the number of inputs (factors and terms) in each term.
  • Asynchronous computation: The non-interactive nature of the computation phase aligns with asynchronous workflows and accelerates the process, as it does not require message exchanges between parties.
  • ITS security: The protocol upholds the ITS inherent in LSSS, meaning it is secure against adversaries with unlimited computing resources and time.

Read the full technical paper on Nillion's MPC Protocol: Evaluation of Arithmetic Sum-of-Products Expressions in Linear Secret Sharing Schemes with a Non-Interactive Computation Phase