DEXON DKG-TSIG Protocol =========================== ### Parameter * λ = MAX(One gossip duraion, transaction confirm latency) * Signature = [BLS](https://en.wikipedia.org/wiki/Boneh%E2%80%93Lynn%E2%80%93Shacham) * Curve = BLS12_381 * n = size of `notary_set` * t = $\left\lfloor\frac{2n}{3}\right\rfloor+1$ ### Notes * Complaints and nack complaints are stored in governance contract; therefore, the broadcast is reliable. * Governance contract will do the sanity check for complaints and nack complaints before adding to its state. * Once a validator proposed `DKGFinal_i`, it can no longer propose any complaint. * After DKG finished, if successful qualify nodes size is less than $\left\lfloor\frac{5}{6}\right\rfloor$ of notary set size, DKG will be rerun with different set of nodes. Phase 1 ID Registration ------- ### @ T < 0 Each validator registers its ID(`DKGMasterPublicKey_i`) with stake. **After λ** Each validator `i` broadcasts a `DKGMasterPublicKeyReady_i` message. Validator waits until seeing more than `2t+1` `DKGGroupPublicKeyReady` message than proceeds to Phase 2. Phase 2 Secret Key Share Exchange ------- ### @ T = 0 Each validator `i` generates `n` (`n` = # of ID registered in phase 1) secret key shares (`SK_i,0, SK_i,1, ..., SK_i,n`) of order `t` and the secret key share is sent to the corresponding validator (`SK_i,j` is sent to validator `j`) via a secure channel. Each validator `i` broadcasts the master public key (`MPK_i = {MPK_i,0, MPK_i,1, ..., MPK_i,t}`) of order `t` associated with the secret key shares. Phase 3 Complaint ------- ### @ T = (0, λ) Each validator `i` calculates public key shares (`PK_0,i, PK_1,i, ..., PK_n,i`) using corresponding master public key (`PK_j,i = F(MPK_j, i)`). Each validator `i` verifies if the secret key share `SK_j,i` is associated with the public key share of validator `j`, `PK_j,i`. If the verification fails, `i` broadcast complaint of `j`, `CMP_i,j`. Phase 4 Nack Complaint ------- ### @ T = λ If validator `i` did not receive `SK_j,i`, broadcast nack complaint of `j`, `NCMP_i,j`. Phase 5 Anti Nack Complaint ------- ### @ T = 2λ If validator `j` sees `NCMP_i,j` for any `i`, broadcast secret key share `SK_j,i`. Phase 6 Rebroadcast Secret ------- ### @ T = 3λ If validator `k` receive `SK_j,i` for the first time for `i` != `k`, broadcast it again. Phase 7 Enforce Complaint ------- ### @ T = 4λ If validator `k` sees `SK_j,i` for `i` != `k`, verifies if the secret key share `SK_j,i` is associated with the public key share of validator `j`, `PK_j,i`. If the verification fails, `k` broadcast complaint of `j`, `CMP_k,j`. If validator `k` sees `NCMP_i,j` for `j` != `k` and did not receive `SK_j,i`, `k` broadcast nack complaint of `j`, `NCMP_k,j`. Phase 8 DKG Finalize ------- ### @ T = 5λ Each validator `i` broadcast a `DKGFinal_i` message. Phase 9 Sign with CSK ------- ### @ T = 6λ Validator waits until seeing more than `2t+1` final message. If there are more than `t` nack complaints to validator `j` ( $\sum_{i} NCMP_{i,j} > t$ (`i` : for all validator `i`)), then `j` is marked as **Disqualified**. If there is **one** complaint, `CMP_i,j`, to validator `j`, then `j` is marked as **Disqualified**. Each validator `i` determines the combined secret key, $CSK_{i} = \sum_{k} SK_{k,i}$ (`k`: validator `k` is not marked as **Disqualified**) If a validator `i` successfully recovered combined secret key, it will broadcast a `DKGSuccess_i` message. Each validator `i` sign the message with `CSK_i` and broadcast the partial signature, `PSign_i`. Each validator `i` determines the combined public key of validator `j`, $CPK_{j} = \sum_{k} PK_{k,j}$ (`k`: validator `k` is not marked as **Disqualified**) Phase 10 TSIG ------- ### @ T = (6λ, +inf) If validator `i` is not **Disqualified**, verify `PSign_i` with `CPK_i`. Collect more than `t` valid `PSign_i` and recover TSIG, `TSIG`. Phase 11 Verify TSIG ------- Determines the group public key, $GPK = \sum_{k} MPK_{k,0}$ (`k`: validator `k` is not marked as **Disqualified**) Verify `TSIG` with `GPK`.