Distribute a secret key into shares

Produces the set of shares that party index would distribute to the other parties under the chosen sharing_scheme. The returned SecretShareMap is opaque; in a real deployment the shares would be serialized and routed over the network to each receiving party, and the receiving parties would store them for use in an abort recovery.

Usage

share_keys(cc, sk, n_parties, threshold, index, sharing_scheme = "additive")

Arguments

cc

A CryptoContext with the MULTIPARTY feature.

sk

The PrivateKey to share.

n_parties

Integer; total number of parties.

threshold

Integer; minimum number of shares needed to reconstruct. For "additive" this must be n_parties - 1; for "shamir" it is typically floor(n_parties/2) + 1.

index

Integer; the 1-based index of the party owning sk (the "my share index").

sharing_scheme

Character; either "additive" (default) or "shamir".

Value

A SecretShareMap suitable for passing to recover_shared_key().

Details

Two sharing schemes are supported:

• "additive" — N-1 threshold; every party must contribute their share to reconstruct. Robust against corruption of any single party's storage but not against any party dropping out.

• "shamir" — floor(N/2) + 1 threshold; the secret can be reconstructed from any majority subset of the distributed shares. Robust against up to floor((N-1)/2) parties dropping out.

See also

recover_shared_key()