Questions about using the Shamir secret sharing protocol

[sda427]

1. Does MPyC support direct input secret sharing? Our own program has already generated secret shares through shamir protocol, and we want to use MPyC for subsequent secure multi-party computation based on shamir protocol, which does not seem to be described in the documentation.
2. Does MPyC support the definition of a variable length data structure in ciphertext?

[lschoe]

The answer to your first question is "yes". For example, if you have say three parties holding secret shares of a secure integer, you can assign these shares locally, for each party, and then they can continue to do secure computation with the resulting secure integer.

Party 0 executes a = secint(secint.field(12723956914977493523)) in its program.
Party 1 executes a = secint(secint.field(7001169756245412185)) in its program.
Party 2 executes a = secint(secint.field(1278382597513330847)) in its program.

Then if they run print(await mpc.output(a)) they should all see 23434 being printed.

About your second question, not sure what it is about?

[farmerj777]

Continuing from sda427 first question, I now have secret shares generated under a specified field (e.g., $10^9$+7). How can I use MPyC to reconstruct and output the original secret value using these shares under the specified field?

[sda427]

Thank you very much for your answer.

The second question is about secure types. When I use secint.array to define a secure array, is there a way to define a variable-length array without specifying the array length? For example, T = secint.array().

[lschoe]

Well, no, Numpy arrays are not variable length. And all entries of a Numpy array are of the same type. This allows for efficient processing, in a vectorized manner. Using lists you can have variable length and elements of mixed type, but that usually incurs some extra costs.