dynamically calculate HB key proposal count, rather than fixed count

rebar.lock

@@ -170,7 +170,7 @@
   3},
  {<<"sibyl">>,
   {git,"https://github.com/helium/sibyl.git",
-       {ref,"7cfcc1f73784578a4fe18ead1264652b87c4571d"}},
+       {ref,"f1a49b2908efa4aa217165e0aebd6d31ab7ad9b2"}},
   0},
  {<<"sidejob">>,{pkg,<<"sidejob">>,<<"2.1.0">>},2},
  {<<"small_ints">>,{pkg,<<"small_ints">>,<<"0.1.0">>},4},

src/miner_val_heartbeat.erl

@@ -147,12 +147,25 @@ generate_poc_keys(Ledger) ->
             case not lists:member(SelfPubKeyBin, IgnoreVals) of
                 true ->
                     %% generate a set of ephemeral keys for POC usage
+                    %% count is based on the num of active validators and the
+                    %% target challenge rate
+                    %% we also have to consider that key proposals are
+                    %% submitted by validators as part of their heartbeats
+                    %% which are only submitted periodically
+                    %% so we need to ensure we have sufficient count of
+                    %% key proposals submitted per HB
+                    %% to help with this we reduce the number of val count
+                    %% by 20% so that we have surplus keys being submitted
                     EphemeralKeyCount =
-                        case blockchain:config(?poc_validator_ephemeral_key_count, Ledger) of
-                            {ok, N} -> N;
-                            _ -> 1
+                        case sibyl_mgr:validator_count() of
+                            NumVals when NumVals > 0 ->
+                                {ok, ChallengeRate} = blockchain_ledger_v1:config(?poc_challenge_rate, Ledger),
+                                {ok, HBInterval} = blockchain_ledger_v1:config(?validator_liveness_interval, Ledger),
+                                round((ChallengeRate / (NumVals * 0.8 )) * HBInterval);
+                            _ ->
+                                0
                         end,
-                    lager:debug("heartbeat ephemeral key count ~p", [EphemeralKeyCount]),
+                    lager:info("heartbeat ephemeral key count ~p", [EphemeralKeyCount]),
                     generate_ephemeral_keys(EphemeralKeyCount);
                 false ->
                     {[], []}