Secure Multi-Party Computation

Secure Multi-Party Computation

Privacy in the Age of Big Data


3 min read

In our hyper-connected world, data is the new oil. From smart homes to self-driving cars, our devices are constantly generating troves of sensitive information. Meanwhile, artificial intelligence and powerful computing are unlocking unprecendented insights from massive datasets.

But there's a catch - organizations can only capitalize on these opportunities if they can access the required data while respecting privacy laws and earning customer trust. This is where secure multi-party computation (MPC) comes in.

What is Secure Multi-Party Computation?

At its core, MPC allows multiple parties to jointly evaluate a function while keeping their inputs private from each other and the party performing the computation. It relies on cryptographic primitives like secret sharing and garbled circuits.

Here's a simple example of securely computing the median of three numbers using Shamir's secret sharing scheme in Python:

from random import randint

# Sharing a secret value
def share_secret(secret_val, num_shares, threshold):
    coeffs = [secret_val] + [randint(0, 2**64) for _ in range(threshold - 1)]
    shares = []
    for i in range(1, num_shares+1):
        x, share_val = i, coeffs[0]
        for j in range(1, len(coeffs)):
            share_val += coeffs[j] * x**(j)
    return shares

# Reconstructing the secret
def reconstruct_secret(shares):
    secret = 0
    for i in range(len(shares)):
        x_product = 1
        for j in range(len(shares)):
            if i != j:
                x_product *= (-j)/(i-j)
        secret += x_product * shares[i]
    return secret

# Alice's input
a = 92

# Bob's input 
b = 67 

# Charlie's input
c = 103

# Sharing inputs
a_shares = share_secret(a, 3, 2)
b_shares = share_secret(b, 3, 2)  
c_shares = share_secret(c, 3, 2)

# Each party sums their shares locally
sum_a = a_shares[0] 
sum_b = b_shares[1]
sum_c = c_shares[2]  

# Reconstructing median 
median = reconstruct_secret(sorted([sum_a, sum_b, sum_c])[1])
print(f"The median is: {median}")

In this example, Alice, Bob, and Charlie share their numbers using Shamir's scheme. They can then locally add up their shares to get the sum of all inputs. Finally, the median can be reconstructed from the middle sum share without revealing individual values.

While basic, this illustrates how parties can compute a joint function while keeping their raw data private - a powerful concept with innumerable applications.

Real-World Use Cases

MPC enables a vast array of privacy-preserving services across different industries:

  • Finance: Private set intersection allows banks to compute joins across customer databases to detect fraud, money laundering, or tax evasion while complying with data protection regulations.

  • Healthcare: Biomedical researchers can run analysis on encrypted clinical data from multiple hospitals to identify treatment patterns without exposing patient records.

  • Supply Chain: Companies can monitor supply chains and optimize logistics by jointly computing over encrypted shipment data from partners.

  • Internet of Things: Smart home devices can leverage MPC to extract insights from sensor data for predictive maintenance without revealing personal user behaviors.

In fact, companies like Apple, Google, and Visa are already using MPC internally and in some of their products and services.

The Rise of Privacy-Preserving Computing

Technologies like MPC are becoming pivotal as we grapple with the tensions between drawing value from data and safeguarding privacy in our digital era. Robust cryptographic protocols allow us to have our cake and eat it too by enabling meaningful analysis while keeping sensitive information encrypted and siloed.

As quantum computing emerges as a threat to classical encryption, new post-quantum secure MPC schemes will be crucial for maintaining privacy. Secure enclaves like those provided by cloud providers further bolster MPC by providing fortified execution environments.

While challenges around efficiency, composability, and ease-of-use remain, MPC is a burgeoning field brimming with opportunity. Continued research and development will unlock a world of privacy-preserving applications that not only protect our data rights, but spur innovation in AI, science, and beyond.