Multiparty computation, or MPC, allows different parties with their own private inputs to conduct a joint computation on their inputs. The parties learn the outcome of the computation, but each learns nothing about the other parties’ respective inputs.
An algorithm created by cryptographer Adi Shamir, called Shamir’s Secret Sharing, lies at the heart of multiparty computation. A secret sharing scheme involves distributing pieces of one secret value (private key) across multiple network nodes or users. Only once a specified subset of the parties pool their pieces together can they retrieve the value.
On its own, this allows us to split data up securely over geographic locations. However, this concept can also apply to performing computational tasks on a secret shared value known as secure MPC.
Using protocols associated with the secret sharing scheme, the parties can perform any computational task on the shared data without needing to bring the associated parts back together.
The secure MPC concept can apply to any type of private data, whether it’s personal data, shared corporate data or a user’s private key.
The traditional demonstrative example is to consider two or more hospitals that wish to conduct a statistical analysis of their patients. With MPC, they can obtain the resulting statistics without ever having to reveal the details of their own patients to the other hospitals.
The same idea can be applied to private keys associated with cryptography. In the hospital example, instead of combining sets of (patient) data, the data (single private key) is instead split into multiple pieces of data, which is then stored in separate locations. These locations can then use MPC to compute any computation using the private key, for example a signature, without the private key needing to be reconstructed.
For example, a Bitcoin private key could be split into pieces, with each piece encrypted separately. Each piece is distributed to a network node. The network can perform computations on the data while keeping the underlying data encrypted and, therefore, private.
The concept of MPC has been around for decades. However, practical use cases have only emerged over more recent years. Now, the technology is finally gaining traction, having been featured in various Gartner Hype Cycles since 2017. MPC is already in use by some of the world’s leading banks and technology firms, protecting assets worth billions of dollars.