Shielded State Sync

Synchronize shielded messages using fuzzy message detection (FMD).

Multi-key extraction

This crate supports multi-key extraction by thresholdizing the original FMD2 scheme.

Knowing up to t < d detection keys leaks no information about the other d-t keys. Here t is a corruption threshold parameter passed to the multi-key extraction.

For each pair (d,t), there is an associated set P(d,t) of valid leaked and filtering rates (p_l,p_f).

• p_l:=2^{-n} and n is the number of (different) secret subkeys across any t detection keys,
• p_f:=2^{-δ}and δ is the total number of secret subkeys in the d detection keys.

Thus, the leaked rate is the false-positive rate at which any coallition of t servers can filter. The filtering rate is the false-positive rate at which the receiver can filter, after receiving all the filters from the d servers.

Key expansion and key randomization

Two implementations are provided. The compact scheme generates short FMD public keys, which can be randomized.

• Compact public keys can be publicly expanded into FMD public keys. This means that only compact keys need to be made public by key owners (receivers), saving bandwidth and storage.
• Randomized public keys share the same set of detection keys. Can be seen as sybil identities for the same receiver.

Serialization

Feature serde enables serialization/deseralization of public keys, secret keys, detection keys, and flag ciphertexts.

Benchmarks

Run make bench.

Examples

See the examples folder.