Add curve25519_keypair/0 and curve25519_shared/2.

src/enacl.erl

@@ -67,6 +67,12 @@
 	verify_32/2
 ]).
 
+%% Curve25519
+-export([
+	curve25519_keypair/0,
+	curve25519_shared/2
+]).
+
 %% Libsodium specific functions (which are also part of the "undocumented" interface to NaCl
 -export([
 	randombytes/1
@@ -168,6 +174,26 @@ verify_16(_, _) -> error(badarg).
 verify_32(X, Y) when is_binary(X), is_binary(Y) -> enacl_nif:crypto_verify_32(X, Y);
 verify_32(_, _) -> error(badarg).
 
+%% Curve 25519 Crypto
+%% ------------------
+%% @doc curve25519_keypair/0 creates a new Public/Secret keypair.
+%%
+%% Generates and returns a new key pair for the Curve 25519 encryption scheme. The return value is a
+%% map in order to avoid using the public key as a secret key and vice versa.
+%% @end.
+-spec curve25519_keypair() -> #{ atom() => binary() }.
+curve25519_keypair() ->
+	<<B0:8/integer, B1:30/binary, B2:8/integer>> = randombytes(32),
+	SK = <<(B0 band 248), B1/binary, (64 bor (B2 band 127))>>,
+	PK = enacl_nif:crypto_curve25519_scalarmult(SK, <<9, 0:248>>),
+	#{ public => PK, secret => SK }.
+
+%% @doc curve25519_shared/2 creates a new shared secret from a given SecretKey and PublicKey.
+%% @end.
+-spec curve25519_shared(SecretKey :: binary(), PublicKey :: binary()) -> binary().
+curve25519_shared(SecretKey, PublicKey) ->
+	enacl_nif:crypto_curve25519_scalarmult(SecretKey, PublicKey).
+
 %% Public Key Crypto
 %% ---------------------
 %% @doc box_keypair/0 creates a new Public/Secret keypair.

src/enacl_nif.erl

@@ -71,6 +71,11 @@
 	crypto_onetimeauth_verify_b/3
 ]).
 
+%% Curve25519
+-export([
+	crypto_curve25519_scalarmult/2
+]).
+
 %% Miscellaneous helper functions
 -export([
 	crypto_hash/1,
@@ -161,6 +166,8 @@ crypto_onetimeauth_b(_Msg, _Key) -> erlang:nif_error(nif_not_loaded).
 crypto_onetimeauth_verify(_Authenticator, _Msg, _Key) -> erlang:nif_error(nif_not_loaded).
 crypto_onetimeauth_verify_b(_Authenticator, _Msg, _Key) -> erlang:nif_error(nif_not_loaded).
 
+crypto_curve25519_scalarmult(_Secret, _BasePoint) -> erlang:nif_error(nif_not_loaded).
+
 crypto_hash(Input) when is_binary(Input) -> erlang:nif_error(nif_not_loaded).
 crypto_hash_b(Input) when is_binary(Input) -> erlang:nif_error(nif_not_loaded).
 crypto_verify_16(_X, _Y) -> erlang:nif_error(nif_not_loaded).