From 9849e7310af455a9dedd075f6c3cf1b43762892e Mon Sep 17 00:00:00 2001
From: Doug Huff <douglas_huff@apple.com>
Date: Wed, 28 Oct 2015 21:45:13 +0000
Subject: [PATCH] Add unsafe_memzero/1

---
 c_src/enacl_nif.c | 16 ++++++++++++++++
 src/enacl.erl     | 14 +++++++++++++-
 src/enacl_nif.erl |  4 +++-
 3 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/c_src/enacl_nif.c b/c_src/enacl_nif.c
index da54551..e759002 100644
--- a/c_src/enacl_nif.c
+++ b/c_src/enacl_nif.c
@@ -81,6 +81,21 @@ ERL_NIF_TERM enif_crypto_verify_32(ErlNifEnv *env, int argc, ERL_NIF_TERM const
 	}
 }
 
+/* This is very unsafe. It will not affect things that have been binary_copy()'ed
+  Use this for destroying key material from ram but nothing more. Be careful! */
+static
+ERL_NIF_TERM enif_sodium_memzero(ErlNifEnv *env, int argc, ERL_NIF_TERM const argv[]) {
+	ErlNifBinary x;
+
+	if ((argc != 1) || (!enif_inspect_binary(env, argv[0], &x))) {
+		return enif_make_badarg(env);
+	}
+
+	sodium_memzero(x.data,x.size);
+
+  return enif_make_atom(env, "ok");
+}
+
 /* Curve 25519 */
 static
 ERL_NIF_TERM enif_crypto_curve25519_scalarmult(ErlNifEnv *env, int argc, ERL_NIF_TERM const argv[]) {
@@ -1172,6 +1187,7 @@ static ErlNifFunc nif_funcs[] = {
 	{"crypto_hash", 1, enif_crypto_hash, ERL_NIF_DIRTY_JOB_CPU_BOUND},
 	{"crypto_verify_16", 2, enif_crypto_verify_16},
 	{"crypto_verify_32", 2, enif_crypto_verify_32},
+	{"sodium_memzero", 1, enif_sodium_memzero},
 
 	{"crypto_curve25519_scalarmult", 2, enif_crypto_curve25519_scalarmult, ERL_NIF_DIRTY_JOB_CPU_BOUND},
 
diff --git a/src/enacl.erl b/src/enacl.erl
index 5e06dc8..75e6ba9 100644
--- a/src/enacl.erl
+++ b/src/enacl.erl
@@ -92,7 +92,8 @@
 -export([
 	hash/1,
 	verify_16/2,
-	verify_32/2
+	verify_32/2,
+  unsafe_memzero/1
 ]).
 
 %% Libsodium specific functions (which are also part of the "undocumented" interface to NaCl
@@ -214,6 +215,17 @@ 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).
 
+%% @doc unsafe_memzero/1 ipmlements guaranteed zero'ing of binary data.
+%%
+%% <p><bold>WARNING:</bold> Take great care. This way be dragons.</p>
+%% <p>This is verify unsafe. If any copies of the binary have been made they are unaffected.
+%% This is intended for use with cryptographic keys where they are only shared within
+%% a running process without copies. This allows removing, eg, symmetric session keys. </p>
+%% @end
+-spec unsafe_memzero(binary()) -> atom().
+unsafe_memzero(X) when is_binary(X) -> enacl_nif:sodium_memzero(X);
+unsafe_memzero(_) -> error(badarg).
+
 %% Public Key Crypto
 %% ---------------------
 %% @doc box_keypair/0 creates a new Public/Secret keypair.
diff --git a/src/enacl_nif.erl b/src/enacl_nif.erl
index 36ab1d1..917e9d4 100644
--- a/src/enacl_nif.erl
+++ b/src/enacl_nif.erl
@@ -109,7 +109,8 @@
 	crypto_hash/1,
 	crypto_hash_b/1,
 	crypto_verify_16/2,
-	crypto_verify_32/2
+	crypto_verify_32/2,
+	sodium_memzero/1
 ]).
 
 %% Access to the RNG
@@ -220,6 +221,7 @@ 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).
 crypto_verify_32(_X, _Y) -> erlang:nif_error(nif_not_loaded).
+sodium_memzero(Input) when is_binary(Input) -> erlang:nif_error(nif_not_loaded).
 
 randombytes(_RequestedSize) -> erlang:nif_error(nif_not_loaded).