edauterman / safetypin Goto Github PK

https://github.com/edauterman/hsm-impl/blob/66e816ca1900977520e4d34886c488f2c793af29/agent/shamir.cc#L106

Just FYI, there are faster (but more complicated) algorithms for interpolation. As the number of parties in the MPC increases this quadratic-time step might be a bottleneck. We can look at implementing one of these other algorithms later on if need be.

See algorithm 10.11 in this book:
https://www.cambridge.org/core/books/modern-computer-algebra/fast-polynomial-evaluation-and-interpolation/7E7AF0E32AB217547BA83B7F6BF06CAA

https://github.com/edauterman/hsm-impl/blob/66e816ca1900977520e4d34886c488f2c793af29/agent/shamir.cc#L215

It looks like Shamir_ValidateShares and Shamir_ReconstructShares are both doing the expensive polynomial interpolation. Instead, you could interpolate the polynomial once (in Shamir_ReconstructShares) and then pass the coefficients of that polynomial to Shamir_ValidateShares, which could check that all of the shares are point on that polynomial.

https://github.com/edauterman/hsm-impl/blob/66e816ca1900977520e4d34886c488f2c793af29/agent/punc_enc.c#L21

Should we be using some authenticated encryption mode (e.g., GCM) instead of ECB mode here?