Provide edoc documentation for the primitives.

src/enacl.erl

@@ -11,6 +11,8 @@
 %%% <p><b>Warning:</b> The cryptographic strength of your implementation is no stronger than
 %%% plaintext cryptography unless you take care in using these primitives correctly. Hence,
 %%% implementors should use these primitives with that in mind.</p>
+%%% <p><b>Note:</b>All functions will fail with a `badarg' error if given incorrect
+%%% parameters.</p>
 %%% @end.
 -module(enacl).
 
@@ -73,24 +75,58 @@ verify_32(X, Y) -> enacl_nif:crypto_verify_32(X, Y).
 
 %% Public Key Crypto
 %% ---------------------
+%% @doc box_keypair/0 creates a new Public/Secret keypair.
+%% Generates and returns a new key pair for the Box encryption scheme.
+%% @end.
+-spec box_keypair() -> {PublicKey, SecretKey}
+  when PublicKey :: binary(),
+       SecretKey :: binary().
 box_keypair() ->
 	enacl_nif:crypto_box_keypair().
 
+%% @doc box/4 encrypts+authenticates a message to another party.
+%% Encrypt a `Msg` to the party identified by public key `PK` using your own secret key `SK` to
+%% authenticate yourself. Requires a `Nonce` in addition. Returns the ciphered message.
+%% @end
+-spec box(Msg, Nonce, PK, SK) -> CipherText
+  when Msg :: binary(),
+       Nonce :: binary(),
+       PK :: binary(),
+       SK :: binary(),
+       CipherText :: binary().
 box(Msg, Nonce, PK, SK) ->
     enacl_nif:crypto_box([p_zerobytes(), Msg], Nonce, PK, SK).
     
+%% @doc box_open/4 decrypts+verifies a message from another party.
+%% Decrypt a `CipherText` into a `Msg` given the other partys public key `PK` and your secret
+%% key `SK`. Also requires the same nonce as was used by the other party. Returns the plaintext
+%% message.
+-spec box_open(CipherText, Nonce, PK, SK) -> Msg
+  when CipherText :: binary(),
+       Nonce :: binary(),
+       PK :: binary(),
+       SK :: binary(),
+       Msg :: binary().
 box_open(CipherText, Nonce, PK, SK) ->
     case enacl_nif:crypto_box_open([p_box_zerobytes(), CipherText], Nonce, PK, SK) of
         {error, Err} -> {error, Err};
         Bin when is_binary(Bin) -> {ok, Bin}
     end.
 
+%% @doc box_nonce_size/0 return the byte-size of the nonce
+%% Used to obtain the size of the nonce.
+%% @end.
+-spec box_nonce_size() -> pos_integer().
 box_nonce_size() ->
 	enacl_nif:crypto_box_NONCEBYTES().
 
+%% @private
+-spec box_public_key_bytes() -> pos_integer().
 box_public_key_bytes() ->
 	enacl_nif:crypto_box_PUBLICKEYBYTES().
 	
+%% @private
+-spec box_secret_key_bytes() -> pos_integer().
 box_secret_key_bytes() ->
 	enacl_nif:crypto_box_SECRETKEYBYTES().