From 2f50ba6289f2f2d9fef05d22a396c0bab4f64149 Mon Sep 17 00:00:00 2001
From: Hans Svensson <hans.svensson@quviq.com>
Date: Mon, 5 Mar 2018 15:19:00 +0100
Subject: [PATCH] Also expose crypto_curve25519_scalarmult_base

---
 c_src/enacl_nif.c | 29 +++++++++++++++++++++++++++++
 src/enacl.erl     | 10 +++++++++-
 src/enacl_nif.erl |  4 +++-
 3 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/c_src/enacl_nif.c b/c_src/enacl_nif.c
index a6d422b..e657bfb 100644
--- a/c_src/enacl_nif.c
+++ b/c_src/enacl_nif.c
@@ -153,6 +153,34 @@ ERL_NIF_TERM enif_crypto_curve25519_scalarmult(ErlNifEnv *env, int argc, ERL_NIF
 	return result;
 }
 
+static
+ERL_NIF_TERM enif_crypto_curve25519_scalarmult_base(ErlNifEnv *env, int argc, ERL_NIF_TERM const argv[]) {
+	ERL_NIF_TERM result;
+	ErlNifBinary secret, output;
+
+	if ((argc != 1) || (!enif_inspect_binary(env, argv[0], &secret))
+			|| (secret.size != crypto_scalarmult_curve25519_BYTES)) {
+		return enif_make_badarg(env);
+	}
+
+	do
+	{
+		if (!enif_alloc_binary(crypto_scalarmult_curve25519_BYTES, &output)) {
+			result = nacl_error_tuple(env, "alloc_failed");
+			continue;
+		}
+
+		if (crypto_scalarmult_curve25519_base(output.data, secret.data) < 0) {
+			result = nacl_error_tuple(env, "scalarmult_curve25519_base_failed");
+			continue;
+		}
+
+		result = enif_make_binary(env, &output);
+	} while (0);
+
+	return result;
+}
+
 /* Ed 25519 */
 static
 ERL_NIF_TERM enif_crypto_sign_ed25519_keypair(ErlNifEnv *env, int argc, ERL_NIF_TERM const argv[]) {
@@ -1698,6 +1726,7 @@ static ErlNifFunc nif_funcs[] = {
 	{"crypto_pwhash_str_verify", 2, enif_crypto_pwhash_str_verify},
 
 	erl_nif_dirty_job_cpu_bound_macro("crypto_curve25519_scalarmult", 2, enif_crypto_curve25519_scalarmult),
+	erl_nif_dirty_job_cpu_bound_macro("crypto_curve25519_scalarmult_base", 1, enif_crypto_curve25519_scalarmult_base),
 
 	erl_nif_dirty_job_cpu_bound_macro("crypto_sign_ed25519_keypair", 0, enif_crypto_sign_ed25519_keypair),
 	{"crypto_sign_ed25519_public_to_curve25519", 1, enif_crypto_sign_ed25519_public_to_curve25519},
diff --git a/src/enacl.erl b/src/enacl.erl
index 10ecc1c..02c4dcd 100644
--- a/src/enacl.erl
+++ b/src/enacl.erl
@@ -83,7 +83,8 @@
 
 %% Curve 25519.
 -export([
-         curve25519_scalarmult/1, curve25519_scalarmult/2
+         curve25519_scalarmult/1, curve25519_scalarmult/2,
+         curve25519_scalarmult_base/1
 ]).
 
 %% Ed 25519.
@@ -905,6 +906,13 @@ curve25519_scalarmult(Secret, BasePoint) ->
 curve25519_scalarmult(#{ secret := Secret, base_point := BasePoint }) ->
     curve25519_scalarmult(Secret, BasePoint).
 
+%% @doc curve25519_scalarmult_base/1 compute the corresponding public key for a
+%% given secret key.
+%% @end.
+-spec curve25519_scalarmult_base(Secret :: binary()) -> binary().
+curve25519_scalarmult_base(Secret) ->
+    enacl_nif:crypto_curve25519_scalarmult_base(Secret).
+
 %% Ed 25519 Crypto
 %% ---------------
 %% @doc crypto_sign_ed25519_keypair/0 creates a new Ed 25519 Public/Secret keypair.
diff --git a/src/enacl_nif.erl b/src/enacl_nif.erl
index 8e807b1..798ef53 100644
--- a/src/enacl_nif.erl
+++ b/src/enacl_nif.erl
@@ -98,7 +98,8 @@
 
 %% Curve25519
 -export([
-         crypto_curve25519_scalarmult/2
+         crypto_curve25519_scalarmult/2,
+         crypto_curve25519_scalarmult_base/1
         ]).
 
 %% Ed 25519
@@ -273,6 +274,7 @@ crypto_onetimeauth_verify(_Authenticator, _Msg, _Key) -> erlang:nif_error(nif_no
 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_curve25519_scalarmult_base(_Secret) -> erlang:nif_error(nif_not_loaded).
 
 crypto_sign_ed25519_keypair() -> erlang:nif_error(nif_not_loaded).
 crypto_sign_ed25519_public_to_curve25519(_PublicKey) -> erlang:nif_error(nif_not_loaded).