Support M-of-N multisig

rebar.config

@@ -12,6 +12,7 @@
 ]}.
 
 {deps, [
+    {multihash, {git, "https://github.com/helium/erlang-multihash.git", {tag, "v2.0.2"}}},
     {ecc_compact, "1.0.5"},
     {enacl, "1.1.1"},
     {erl_base58, "0.0.1"},

rebar.lock

@@ -4,6 +4,10 @@
  {<<"enacl">>,{pkg,<<"enacl">>,<<"1.1.1">>},0},
  {<<"erl_base58">>,{pkg,<<"erl_base58">>,<<"0.0.1">>},0},
  {<<"multiaddr">>,{pkg,<<"multiaddr">>,<<"1.1.3">>},0},
+ {<<"multihash">>,
+  {git,"https://github.com/helium/erlang-multihash.git",
+       {ref,"d2057bf37d580d840dbd64918c768ef210f7d298"}},
+  0},
  {<<"small_ints">>,{pkg,<<"small_ints">>,<<"0.1.0">>},1}]}.
 [
 {pkg_hash,[

src/libp2p_crypto.app.src

@@ -23,6 +23,7 @@
                   enacl,
                   ecc_compact,
                   multiaddr,
+                  multihash,
                   erl_base58
                  ]},
   {env,[]},

src/libp2p_crypto.erl

@@ -11,6 +11,7 @@
 %% the type of keythat follows in the binary (KEYTYPE).
 -define(KEYTYPE_ECC_COMPACT, 0).
 -define(KEYTYPE_ED25519, 1).
+-define(KEYTYPE_MULTISIG, 2).
 -define(NETTYPE_MAIN, 0).
 -define(NETTYPE_TEST, 1).
 
@@ -22,7 +23,8 @@
 
 -type pubkey() ::
     {ecc_compact, ecc_compact:public_key()}
-    | {ed25519, enacl_pubkey()}.
+    | {ed25519, enacl_pubkey()}
+    | {multisig_m_of_n, pos_integer(), pos_integer(), binary()}.
 
 -type pubkey_bin() :: <<_:8, _:_*8>>.
 -type sig_fun() :: fun((binary()) -> binary()).
@@ -240,7 +242,9 @@ pubkey_to_bin(Network, {ecc_compact, PubKey}) ->
             erlang:error(not_compact)
     end;
 pubkey_to_bin(Network, {ed25519, PubKey}) ->
-    <<(from_network(Network)):4, ?KEYTYPE_ED25519:4, PubKey/binary>>.
+    <<(from_network(Network)):4, ?KEYTYPE_ED25519:4, PubKey/binary>>;
+pubkey_to_bin(Network, {multisig_m_of_n, M, N, KeysDigest}) ->
+    <<(from_network(Network)):4, ?KEYTYPE_MULTISIG:4, M/integer, N/integer, KeysDigest/binary>>.
 
 %% @doc Convertsa a given binary encoded public key to a tagged public
 %% key. The key is asserted to be on the current active network.
@@ -260,6 +264,11 @@ bin_to_pubkey(Network, <<NetType:4, ?KEYTYPE_ED25519:4, PubKey:32/binary>>) ->
     case NetType == from_network(Network) of
         true -> {ed25519, PubKey};
         false -> erlang:error({bad_network, NetType})
+    end;
+bin_to_pubkey(Network, <<NetType:4, ?KEYTYPE_MULTISIG:4, M/integer, N/integer, KeysDigest/binary>>) ->
+    case NetType == from_network(Network) of
+        true -> {multisig_m_of_n, M, N, KeysDigest};
+        false -> erlang:error({bad_network, NetType})
     end.
 
 %% @doc Converts a public key to base58 check encoded string
@@ -299,6 +308,34 @@ to_network(?NETTYPE_TEST) -> testnet.
 %% @doc Verifies a binary against a given digital signature over the
 %% sha256 of the binary.
 -spec verify(binary(), binary(), pubkey()) -> boolean().
+verify(Bin, Signature, {multisig_m_of_n, M, N, KeysDigest}) ->
+    KeySize = 32, % TODO Macro?
+    KeysLen = N * KeySize,
+    <<KeysBin:KeysLen/binary, ISigsBin/binary>> = Signature,
+    {ok, HashType} = multihash:hash(KeysDigest),
+    case multihash:digest(KeysBin, HashType) of
+        {ok, KeysDigest} ->
+            % TODO Sort keys before or after decoding?
+            Keys =
+                lists:map(
+                    fun bin_to_pubkey/1,
+                    lists:sort(fun pubkey_bin_cmp/2, bin_split(KeysBin, KeySize))
+                ),
+            KeySigs =
+                bin_fold(
+                    fun (<<I:8/integer, Rest0/binary>>, KeySigs) ->
+                        Key = lists:nth(I, Keys),
+                        Size = sig_size(Key),
+                        <<Sig:Size, Rest1/binary>> = Rest0,
+                        {Rest1, [{Key, Sig} | KeySigs]}
+                    end,
+                    [],
+                    ISigsBin
+                ),
+            M =< length([{} || {K, S} <- KeySigs, verify(Bin, S, K)]);
+        _ ->
+            false
+    end;
 verify(Bin, Signature, {ecc_compact, PubKey}) ->
     public_key:verify(Bin, sha256, Signature, PubKey);
 verify(Bin, Signature, {ed25519, PubKey}) ->
@@ -335,6 +372,11 @@ b58_to_version_bin(Str) ->
         {error, Reason} -> error(Reason)
     end.
 
+-spec pubkey_bin_cmp(binary(), binary()) -> boolean().
+pubkey_bin_cmp(<<A/binary>>, <<B/binary>>) ->
+    % TODO Something smarter?
+    A > B.
+
 %% @doc Converts a given binary public key to a P2P address.
 %%
 %% @see p2p_to_pubkey_bin/1
@@ -370,6 +412,24 @@ base58check_decode(B58) ->
             {error, bad_checksum}
     end.
 
+-spec sig_size(pubkey()) -> pos_integer().
+sig_size({ecc_compact, _}) -> 560;
+sig_size({ed25519    , _}) -> 512.
+
+-spec bin_fold(fun((binary(), A) -> {binary(), A}), A, binary()) -> A.
+bin_fold(_, Acc, <<>>) ->
+    Acc;
+bin_fold(F, Acc0, <<Bin0/binary>>) ->
+    {<<Bin1/binary>>, Acc1} = F(Bin0, Acc0),
+    bin_fold(F, Acc1, Bin1).
+
+-spec bin_split(B, pos_integer()) -> [B] when B :: binary().
+bin_split(<<>>, _) ->
+    [];
+bin_split(<<Bin/binary>>, ChunkSize) ->
+    <<Chunk:ChunkSize/binary, Rest/binary>> = Bin,
+    [Chunk | bin_split(Rest, ChunkSize)].
+
 -ifdef(TEST).
 
 -include_lib("eunit/include/eunit.hrl").