missing comments/external documentation on usage preconditions?

[bennetyee]

oasis-core/secret-sharing/src/churp/switch.rs

Line 146 in 8f2032a

pub(crate) fn start_accumulating(&self, vm: VerificationMatrix<G>) -> Result<()> {

comments / separate documentation should exist for recommendations for how to use this / assumptions / interface requirements.

all shareholders must get the same verification matrix, since otherwise different shareholders will accept different zero-hole polynomials and the shareholders will diverge and be unable to reconstruct the master secret unless some additional checking is done prior to committing to the dimension switched values. this is not the responsibility of the secret sharing code, but the user of the library -- presumably there will have to be consensus on what the verification matrix is among all the shareholders, so it's natural to just require a hash of the verification matrix to be committed to the blockchain, but other approaches would be fine too.