Use constant time memcmp() when comparing packet HMACs.

[oweals/tinc.git] / src / utils.c

diff --git a/src/utils.c b/src/utils.c
index 3b221f59f0ef731f62b0369314de5964bdf855fd..c629ae0b50cd94a5b0169ca868e6f2c55357a525 100644 (file)
--- a/src/utils.c
+++ b/src/utils.c
@@ -78,3 +78,18 @@ unsigned int bitfield_to_int(const void *bitfield, size_t size) {
        memcpy(&value, bitfield, size);
        return value;
 }
+
+/**
+ * As memcmp(), but constant-time.
+ * Returns 0 when data is equal, non-zero otherwise.
+ */
+int memcmp_constant_time (const void *a, const void *b, size_t size) {
+  const uint8_t *a1 = a, *b1 = b;
+  int ret = 0;
+  size_t i;
+
+  for (i = 0; i < size; i++)
+      ret |= *a1++ ^ *b1++;
+
+  return ret;
+}