fe25519: Fix integer types of fe25519_iszero()

Fixes T188

Signed-off-by: Andreas Schneider <asn@cryptomilk.org>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>

include/libssh/fe25519.h

@@ -39,7 +39,7 @@ void fe25519_unpack(fe25519 *r, const unsigned char x[32]);
 
 void fe25519_pack(unsigned char r[32], const fe25519 *x);
 
-int fe25519_iszero(const fe25519 *x);
+uint32_t fe25519_iszero(const fe25519 *x);
 
 int fe25519_iseq_vartime(const fe25519 *x, const fe25519 *y);
 

src/external/fe25519.c

@@ -120,10 +120,10 @@ void fe25519_pack(unsigned char r[32], const fe25519 *x)
     }
 }
 
-int fe25519_iszero(const fe25519 *x)
+uint32_t fe25519_iszero(const fe25519 *x)
 {
     int i;
-    int r;
+    uint32_t r;
 
     fe25519 t = *x;
     fe25519_freeze(&t);