1 files changed, 39 insertions, 0 deletions
diff --git a/test-noncanon.c b/test-noncanon.c
new file mode 100644
index 0000000..6de4e8d
--- /dev/null
+++ b/test-noncanon.c
@@ -0,0 +1,39 @@
+/* This file can be used to test whether the code handles non-canonical curve
+ * points (i.e. points with the 256th bit set) in the same way as the reference
+ * implementation. */
+
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+
+extern void curve25519_donna(unsigned char *output, const unsigned char *a,
+                             const unsigned char *b);
+int
+main()
+{
+  static const uint8_t point1[32] = {
+    0x25,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
+    0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
+    0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
+    0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
+  };
+  static const uint8_t point2[32] = {
+    0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
+    0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
+    0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
+    0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
+  };
+  static const uint8_t scalar[32] = { 1 };
+  uint8_t out1[32], out2[32];
+
+  curve25519_donna(out1, scalar, point1);
+  curve25519_donna(out2, scalar, point2);
+
+  if (0 == memcmp(out1, out2, sizeof(out1))) {
+    fprintf(stderr, "Top bit not ignored.\n");
+    return 1;
+  }
+
+  fprintf(stderr, "Top bit correctly ignored.\n");
+  return 0;
+}