security: use EVP_DigestVerify* routines in VerifierFilter

Change-Id: I2f5323fee86dd08c16552c2310b3181a620013b5
diff --git a/src/security/transform/verifier-filter.hpp b/src/security/transform/verifier-filter.hpp
index e08cc7d..34e3c1d 100644
--- a/src/security/transform/verifier-filter.hpp
+++ b/src/security/transform/verifier-filter.hpp
@@ -35,6 +35,8 @@
  * @brief The module to verify signatures.
  *
  * The next module in the chain is usually BoolSink.
+ *
+ * @note This module cannot be used to verify HMACs.
  */
 class VerifierFilter : public Transform
 {