diff --git a/eqc_test/enacl_eqc.erl b/eqc_test/enacl_eqc.erl
index b1aa1d6..bb6eae3 100644
--- a/eqc_test/enacl_eqc.erl
+++ b/eqc_test/enacl_eqc.erl
@@ -115,6 +115,73 @@ prop_box_failure_integrity() ->
             end
         end).
 
+%% SIGNATURES
+%% ----------
+
+prop_sign_keypair() ->
+    ?FORALL(_D, return(dummy),
+      begin
+        #{ public := _, secret := _ } = enacl:sign_keypair(),
+        true
+      end).
+
+sign_keypair_bad() ->
+  ?LET(X, elements([pk, sk]),
+    begin
+      KP = enacl:sign_keypair(),
+      case X of
+        pk ->
+          Sz = enacl:sign_keypair_public_size(),
+          ?LET(Wrong, oneof([a, int(), ?SUCHTHAT(B, binary(), byte_size(B) /= Sz)]),
+            KP#{ public := Wrong });
+        sk ->
+          Sz = enacl:sign_keypair_secret_size(),
+          ?LET(Wrong, oneof([a, int(), ?SUCHTHAT(B, binary(), byte_size(B) /= Sz)]),
+            KP#{ secret := Wrong })
+      end
+    end).
+
+sign_keypair_good() ->
+  return(enacl:sign_keypair()).
+
+sign_keypair() ->
+  fault(sign_keypair_bad(), sign_keypair_good()).
+
+sign_keypair_public_valid(#{ public := Public })
+  when is_binary(Public) ->
+    byte_size(Public) == enacl:sign_keypair_public_size();
+sign_keypair_public_valid(_) -> false.
+    
+sign_keypair_secret_valid(#{ secret := Secret })
+  when is_binary(Secret) ->
+    byte_size(Secret) == enacl:sign_keypair_secret_size();
+sign_keypair_secret_valid(_) -> false.
+    
+sign_keypair_valid(KP) ->
+  sign_keypair_public_valid(KP) andalso sign_keypair_secret_valid(KP).
+
+prop_sign() ->
+    ?FORALL({Msg, KeyPair}, {binary(), fault_rate(1, 40, sign_keypair())},
+      begin
+        case sign_keypair_secret_valid(KeyPair) of
+          true ->
+            #{ secret := Secret } = KeyPair,
+            enacl:sign(Msg, Secret),
+            true;
+          false ->
+            #{ secret := Secret } = KeyPair,
+            badargs(fun() -> enacl:sign(Msg, Secret) end)
+        end
+      end).
+
+prop_sign_open() ->
+    ?FORALL({Msg, KeyPair}, {binary(), sign_keypair()},
+      begin
+        #{ public := Public, secret := Secret } = KeyPair,
+        SM = enacl:sign(Msg, Secret),
+        equals({ok, Msg}, enacl:sign_open(SM, Public))
+      end).
+      
 %% CRYPTO SECRET BOX
 %% -------------------------------
 
diff --git a/src/enacl.erl b/src/enacl.erl
index 64c785e..58c778c 100644
--- a/src/enacl.erl
+++ b/src/enacl.erl
@@ -25,6 +25,8 @@
 	box_public_key_bytes/0,
 	box_secret_key_bytes/0,
 	
+	sign_keypair_public_size/0,
+	sign_keypair_secret_size/0,
 	sign_keypair/0,
 	sign/2,
 	sign_open/2
@@ -147,13 +149,21 @@ box_public_key_bytes() ->
 
 %% Signatures
 
+%% @private
+sign_keypair_public_size() ->
+    enacl_nif:crypto_sign_PUBLICKEYBYTES().
+    
+%% @private
+sign_keypair_secret_size() ->
+    enacl_nif:crypto_sign_SECRETKEYBYTES().
+
 %% @doc sign_keypair/0 returns a signature keypair for signing
 %% The returned value is a map in order to make it harder to misuse keys.
 %% @end
 -spec sign_keypair() -> KeyMap
   when KeyMap :: maps:map(atom(), binary()).
 sign_keypair() ->
-    {PK, SK} = enacl_nif:sign_keypair(),
+    {PK, SK} = enacl_nif:crypto_sign_keypair(),
     #{ public => PK, secret => SK}.
 
 %% @doc sign/2 signs a message with a digital signature identified by a secret key.
@@ -164,7 +174,7 @@ sign_keypair() ->
     M :: binary(),
     SK :: binary(),
     SM :: binary().
-sign(M, SK) -> enacl_nif:sign(M, SK).
+sign(M, SK) -> enacl_nif:crypto_sign(M, SK).
 
 %% @doc sign_open/2 opens a digital signature
 %% Given a signed message `SM' and a public key `PK', verify that the message has the right signature. Returns either
@@ -175,7 +185,11 @@ sign(M, SK) -> enacl_nif:sign(M, SK).
     SM :: binary(),
     PK :: binary(),
     M :: binary().
-sign_open(SM, PK) -> enacl_nif:sign_open(SM, PK).
+sign_open(SM, PK) ->
+    case enacl_nif:crypto_sign_open(SM, PK) of
+        M when is_binary(M) -> {ok, M};
+        {error, Err} -> {error, Err}
+    end.
 
 %% @private
 -spec box_secret_key_bytes() -> pos_integer().