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Address bugs in BBA protocol's use of common coin (#11)
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* Add an extra CONF message round after the AUX round
* Track bval messages broadcasted in each round
* Add another test for ensuring that BBA terminates
* Allow peers to send both 0 and 1 in the same round and track it in the witness
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@vihu
vihu authored May 10, 2018
1 parent fc02ff7 commit 72253f3
Showing 1 changed file with 125 additions and 31 deletions.
156 changes: 125 additions & 31 deletions src/hbbft_bba.erl
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Original file line number Diff line number Diff line change
Expand Up @@ -13,8 +13,10 @@
n :: pos_integer(),
witness = maps:new() :: #{non_neg_integer() => 0 | 1},
aux_witness = maps:new() :: #{non_neg_integer() => 0 | 1},
conf_witness = maps:new() :: #{non_neg_integer() => 0 | 1},
aux_sent = false :: boolean(),
broadcasted = 2#0 :: 0 | 1,
conf_sent = false :: boolean(),
broadcasted = 2#0 :: 0 | 1 | 2 | 3,
bin_values = 2#00 :: 0 | 1 | 2 | 3
}).

Expand All @@ -28,8 +30,10 @@
n :: pos_integer(),
witness = maps:new() :: #{non_neg_integer() => 0 | 1},
aux_witness = maps:new() :: #{non_neg_integer() => 0 | 1},
conf_witness = maps:new() :: #{non_neg_integer() => 0 | 1},
aux_sent = false :: boolean(),
broadcasted = 2#0 :: 0 | 1,
conf_sent = false :: boolean(),
broadcasted = 2#0 :: 0 | 1 | 2 | 3,
bin_values = 2#00 :: 0 | 1 | 2 | 3
}).

Expand All @@ -38,10 +42,11 @@

-type bval_msg() :: {bval, non_neg_integer(), 0 | 1}.
-type aux_msg() :: {aux, non_neg_integer(), 0 | 1}.
-type conf_msg() :: {conf, non_neg_integer(), 0 | 1}.
-type coin_msg() :: {{coin, non_neg_integer()}, hbbft_cc:share_msg()}.
-type msgs() :: bval_msg() | aux_msg() | coin_msg().
-type msgs() :: bval_msg() | aux_msg() | conf_msg() | coin_msg().

-export_type([bba_data/0, bba_serialized_data/0, bval_msg/0, aux_msg/0, coin_msg/0, msgs/0]).
-export_type([bba_data/0, bba_serialized_data/0, bval_msg/0, aux_msg/0, coin_msg/0, msgs/0, conf_msg/0]).

-spec init(tpke_privkey:privkey(), pos_integer(), non_neg_integer()) -> bba_data().
init(SK, N, F) ->
Expand All @@ -53,22 +58,25 @@ init(SK, N, F) ->
%% – bin_values {}
-spec input(bba_data(), 0 | 1) -> {bba_data(), ok | {send, [hbbft_utils:multicast(bval_msg())]}}.
input(Data = #bba_data{state=init}, BInput) ->
{Data#bba_data{est = BInput}, {send, [{multicast, {bval, Data#bba_data.round, BInput}}]}};
{Data#bba_data{est = BInput, broadcasted=add(BInput, Data#bba_data.broadcasted)}, {send, [{multicast, {bval, Data#bba_data.round, BInput}}]}};
input(Data = #bba_data{state=done}, _BInput) ->
{Data, ok}.

-spec handle_msg(bba_data(), non_neg_integer(),
coin_msg() |
bval_msg() |
aux_msg()) -> {bba_data(), ok} |
{bba_data(), {send, [hbbft_utils:multicast(bval_msg() | aux_msg() | coin_msg())]}} |
{bba_data(), {result, 0 | 1}}.
aux_msg() |
conf_msg()) -> {bba_data(), ok} |
{bba_data(), {send, [hbbft_utils:multicast(bval_msg() | aux_msg() | conf_msg() | coin_msg())]}} |
{bba_data(), {result, 0 | 1}}.
handle_msg(Data = #bba_data{state=done}, _J, _BInput) ->
{Data, ok};
handle_msg(Data = #bba_data{round=R}, J, {bval, R, V}) ->
bval(Data, J, V);
handle_msg(Data = #bba_data{round=_R}, J, {aux, _R, V}) ->
aux(Data, J, V);
handle_msg(Data = #bba_data{round=_R}, J, {conf, _R, V}) ->
conf(Data, J, V);
handle_msg(Data = #bba_data{round=R, coin=Coin}, J, {{coin, R}, CMsg}) when Coin /= undefined ->
%% dispatch the message to the nested coin protocol
case hbbft_cc:handle_msg(Data#bba_data.coin, J, CMsg) of
Expand Down Expand Up @@ -111,8 +119,8 @@ handle_msg(Data, _J, _Msg) ->
-spec bval(bba_data(), non_neg_integer(), 0 | 1) -> {bba_data(), {send, [hbbft_utils:multicast(aux_msg() | coin_msg())]}}.
bval(Data=#bba_data{n=N, f=F}, Id, V) ->
%% add to witnesses
Witness = maps:put(Id, V, Data#bba_data.witness),
WitnessCount = lists:sum([ 1 || {_, Val} <- maps:to_list(Witness), V == Val ]),
Witness = add_witness(Id, V, Data#bba_data.witness),
WitnessCount = lists:sum([ 1 || {_, Val} <- maps:to_list(Witness), has(V, Val) ]),

{NewData, ToSend} = case WitnessCount >= F+1 andalso not has(V, Data#bba_data.broadcasted) of
true ->
Expand Down Expand Up @@ -140,29 +148,59 @@ bval(Data=#bba_data{n=N, f=F}, Id, V) ->
{NewData2, ToSend}
end,

case check_n_minus_f_aux_messages(N, F, NewData3) of
true when NewData3#bba_data.coin == undefined ->
%% instantiate the common coin
%% TODO need more entropy for the SID
{CoinData, {send, CoinSend}} = hbbft_cc:get_coin(hbbft_cc:init(NewData3#bba_data.secret_key, term_to_binary({NewData3#bba_data.round}), N, F)),
{NewData3#bba_data{coin=CoinData}, {send, hbbft_utils:wrap({coin, Data#bba_data.round}, CoinSend) ++ ToSend2}};
_ ->
%% check if we have n-f aux messages
case threshold(N, F, NewData3, aux) of
true ->
%% check if we have n-f conf messages
case threshold(N, F, NewData3, conf) of
%% instantiate the common coin
true when NewData3#bba_data.coin == undefined ->
%% TODO need more entropy for the SID
{CoinData, {send, CoinSend}} = hbbft_cc:get_coin(hbbft_cc:init(NewData3#bba_data.secret_key, term_to_binary({NewData3#bba_data.round}), N, F)),
{NewData3#bba_data{coin=CoinData}, {send, hbbft_utils:wrap({coin, Data#bba_data.round}, CoinSend) ++ ToSend2}};
_ ->
{NewData3, {send, ToSend2}}
end;
false ->
{NewData3, {send, ToSend2}}
end;
false ->
{NewData, {send, ToSend}}
end.

-spec aux(bba_data(), non_neg_integer(), 0 | 1) -> {bba_data(), ok | {send, [hbbft_utils:multicast(coin_msg())]}}.
-spec aux(bba_data(), non_neg_integer(), 0 | 1) -> {bba_data(), ok | {send, [hbbft_utils:multicast(conf_msg())]}}.
aux(Data = #bba_data{n=N, f=F}, Id, V) ->
Witness = maps:put(Id, V, Data#bba_data.aux_witness),
Witness = add_witness(Id, V, Data#bba_data.aux_witness),
NewData = Data#bba_data{aux_witness = Witness},
case check_n_minus_f_aux_messages(N, F, NewData) of
true when NewData#bba_data.coin == undefined ->
%% instantiate the common coin
%% TODO need more entropy for the SID
{CoinData, {send, ToSend}} = hbbft_cc:get_coin(hbbft_cc:init(NewData#bba_data.secret_key, term_to_binary({NewData#bba_data.round}), N, F)),
{NewData#bba_data{coin=CoinData}, {send, hbbft_utils:wrap({coin, Data#bba_data.round}, ToSend)}};
case threshold(N, F, NewData, aux) of
true->
%% only send conf after n-f aux messages
case NewData#bba_data.conf_sent of
false ->
{NewData#bba_data{conf_sent=true}, {send, [{multicast, {conf, NewData#bba_data.round, NewData#bba_data.bin_values}}]}};
true ->
%% conf was already sent
{NewData, ok}
end;
_ ->
{NewData, ok}
end.

-spec conf(bba_data(), non_neg_integer(), 0 | 1) -> {bba_data(), ok | {send, [hbbft_utils:multicast(coin_msg())]}}.
conf(Data = #bba_data{n=N, f=F}, Id, V) ->
Witness = maps:put(Id, V, Data#bba_data.conf_witness),
NewData = Data#bba_data{conf_witness = Witness},
case threshold(N, F, NewData, aux) of
true->
case threshold(N, F, NewData, conf) of
true when NewData#bba_data.coin == undefined ->
%% instantiate the common coin
%% TODO need more entropy for the SID
{CoinData, {send, ToSend}} = hbbft_cc:get_coin(hbbft_cc:init(NewData#bba_data.secret_key, term_to_binary({NewData#bba_data.round}), N, F)),
{NewData#bba_data{coin=CoinData}, {send, hbbft_utils:wrap({coin, NewData#bba_data.round}, ToSend)}};
_ ->
{NewData, ok}
end;
_ ->
{NewData, ok}
end.
Expand All @@ -177,7 +215,9 @@ serialize(#bba_data{state=State,
n=N,
witness=Witness,
aux_witness=AuxWitness,
conf_witness=ConfWitness,
aux_sent=AuxSent,
conf_sent=ConfSent,
broadcasted=Broadcasted,
bin_values=BinValues}) ->
NewCoin = case Coin of
Expand All @@ -193,11 +233,12 @@ serialize(#bba_data{state=State,
n=N,
witness=Witness,
aux_witness=AuxWitness,
conf_witness=ConfWitness,
aux_sent=AuxSent,
conf_sent=ConfSent,
broadcasted=Broadcasted,
bin_values=BinValues}.


-spec deserialize(bba_serialized_data(), tpke_privkey:privkey()) -> bba_data().
deserialize(#bba_serialized_data{state=State,
round=Round,
Expand All @@ -208,7 +249,9 @@ deserialize(#bba_serialized_data{state=State,
n=N,
witness=Witness,
aux_witness=AuxWitness,
conf_witness=ConfWitness,
aux_sent=AuxSent,
conf_sent=ConfSent,
broadcasted=Broadcasted,
bin_values=BinValues}, SK) ->
NewCoin = case Coin of
Expand All @@ -225,22 +268,31 @@ deserialize(#bba_serialized_data{state=State,
n=N,
witness=Witness,
aux_witness=AuxWitness,
conf_witness=ConfWitness,
aux_sent=AuxSent,
conf_sent=ConfSent,
broadcasted=Broadcasted,
bin_values=BinValues}.


%% helper functions
-spec check_n_minus_f_aux_messages(pos_integer(), non_neg_integer(), bba_data()) -> boolean().
check_n_minus_f_aux_messages(N, F, Data) ->
%% check if we've received at least N - F AUX messages where the values in the AUX messages are member of bin_values

-spec threshold(pos_integer(), non_neg_integer(), bba_data(), aux | conf) -> boolean().
threshold(N, F, Data, Msg) ->
case Msg of
aux -> check(N, F, Data#bba_data.bin_values, Data#bba_data.aux_witness, fun subset/2);
conf -> check(N, F, Data#bba_data.bin_values, Data#bba_data.conf_witness, fun subset/2)
end.

-spec check(pos_integer(), non_neg_integer(), 0 | 1 | 2 | 3, #{non_neg_integer() => 0 | 1}, fun((0|1|2|3, 0|1|2|3) -> boolean())) -> boolean().
check(N, F, ToCheck, Map, Fun) ->
maps:fold(fun(_, V, Acc) ->
case has(V, Data#bba_data.bin_values) of
case Fun(V, ToCheck) of
true ->
Acc + 1;
false -> Acc
end
end, 0, Data#bba_data.aux_witness) >= N - F.
end, 0, Map) >= N - F.

%% add X to set Y
add(X, Y) ->
Expand All @@ -250,6 +302,10 @@ add(X, Y) ->
has(X, Y) ->
((1 bsl X) band Y) /= 0.

%% is X a subset of Y?
subset(X, Y) ->
(X band Y) == X.

%% count elements of set
count(2#0) -> 0;
count(2#1) -> 1;
Expand All @@ -265,6 +321,10 @@ rand_val(2#11) -> hd(hbbft_utils:random_n(1, [0, 1])).
val(2#1) -> 0;
val(2#10) -> 1.

add_witness(Id, Value, Witness) ->
Old = maps:get(Id, Witness, 0),
maps:put(Id, add(Value, Old), Witness).

-ifdef(TEST).
-include_lib("eunit/include/eunit.hrl").

Expand Down Expand Up @@ -352,6 +412,40 @@ init_with_mixed_zeros_and_ones_test_() ->
ok
end}.

termination_test_() ->
Fun = fun(Vals) ->
fun() ->
N = 7,
F = 2,
dealer:start_link(N, F+1, 'SS512'),
{ok, _PubKey, PrivateKeys} = dealer:deal(),
gen_server:stop(dealer),
States = [hbbft_bba:init(Sk, N, F) || Sk <- PrivateKeys],
StatesWithId = lists:zip(lists:seq(0, length(States) - 1), States),
MixedList = lists:zip(Vals, StatesWithId),
%% all valid members should call get_coin
Res = lists:map(fun({I, {J, State}}) ->
{NewState, Result} = input(State, I),
{{J, NewState}, {J, Result}}
end, MixedList),
{NewStates, Results} = lists:unzip(Res),
{_FinalStates, ConvergedResults} = hbbft_test_utils:do_send_outer(?MODULE, Results, NewStates, sets:new()),
DistinctResults = sets:from_list([BVal || {result, {_, BVal}} <- sets:to_list(ConvergedResults)]),
?assertEqual(N, sets:size(ConvergedResults)),
?assertEqual(1, sets:size(DistinctResults)),
ok
end
end,
[
Fun([1, 0, 0, 0, 0, 0, 0]),
Fun([1, 1, 0, 0, 0, 0, 0]),
Fun([1, 1, 1, 0, 0, 0, 0]),
Fun([1, 1, 1, 1, 0, 0, 0]),
Fun([1, 1, 1, 1, 1, 0, 0]),
Fun([1, 1, 1, 1, 1, 1, 0]),
Fun([1, 1, 1, 1, 1, 1, 1])
].

one_dead_test() ->
N = 5,
F = 1,
Expand Down

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