Implement crypto boxing/unboxing for public key cryptographic systems.

src/enacl.erl

@@ -1,8 +1,14 @@
 -module(enacl).
 
 -export([
-	hash/1,
-	box_keypair/0
+	box_keypair/0,
+	box/4,
+	box_open/4,
+	box_nonce_size/0
+]).
+
+-export([
+	hash/1
 ]).
 
 hash(Bin) ->
@@ -11,3 +17,21 @@ hash(Bin) ->
 box_keypair() ->
 	enacl_nif:crypto_box_keypair().
 
+box(Msg, Nonce, PK, SK) ->
+    enacl_nif:crypto_box([zerobytes(), Msg], Nonce, PK, SK).
+    
+box_open(CipherText, Nonce, PK, SK) ->
+    case enacl_nif:crypto_box_open([box_zerobytes(), CipherText], Nonce, PK, SK) of
+        {error, Err} -> {error, Err};
+        Bin when is_binary(Bin) -> {ok, Bin}
+    end.
+
+box_nonce_size() ->
+	enacl_nif:crypto_box_NONCEBYTES().
+
+%% Helpers
+zerobytes() ->
+	binary:copy(<<0>>, enacl_nif:crypto_box_ZEROBYTES()).
+	
+box_zerobytes() ->
+	binary:copy(<<0>>, enacl_nif:crypto_box_BOXZEROBYTES()).

src/enacl_nif.erl

@@ -1,9 +1,22 @@
+%%% @doc module enacl_nif provides the low-level interface to the NaCl/Sodium NIFs.
+%%% @end
 -module(enacl_nif).
 
+%% Public key auth
 -export([
-	crypto_hash/1,
-	crypto_box_keypair/0
+	crypto_box_keypair/0,
+	crypto_box/4,
+	crypto_box_open/4,
+	crypto_box_NONCEBYTES/0,
+	crypto_box_ZEROBYTES/0,
+	crypto_box_BOXZEROBYTES/0
 ]).
+
+%% Miscellaneous helper functions
+-export([
+	crypto_hash/1
+]).
+
 -on_load(init/0).
 
 init() ->
@@ -16,6 +29,16 @@ init() ->
 		end, atom_to_list(?MODULE)),
 	erlang:load_nif(SoName, 0).
 
-crypto_hash(Input) when is_binary(Input) -> error({nif_not_loaded, ?MODULE}).
-crypto_box_keypair() -> error({nif_not_loaded, ?MODULE}).
+not_loaded() ->
+    error({nif_not_loaded, ?MODULE}).
+
+crypto_box_NONCEBYTES() -> not_loaded().
+crypto_box_ZEROBYTES() -> not_loaded().
+crypto_box_BOXZEROBYTES() -> not_loaded().
+crypto_box_keypair() -> not_loaded().
+crypto_box(_PaddedMsg, _Nonce, _PK, _SK) -> not_loaded().
+crypto_box_open(_CipherText, _Nonce, _PK, _SK) -> not_loaded().
+
+crypto_hash(Input) when is_binary(Input) -> not_loaded().
+