security: use EVP_DigestSign* routines in SignerFilter

Change-Id: Ib87c4681084bf0389de527450a2248fe2161e6ee
diff --git a/tests/unit-tests/security/transform/public-key.t.cpp b/tests/unit-tests/security/transform/public-key.t.cpp
index 41b0582..fee246f 100644
--- a/tests/unit-tests/security/transform/public-key.t.cpp
+++ b/tests/unit-tests/security/transform/public-key.t.cpp
@@ -114,6 +114,7 @@
   PublicKey pKey;
   pKey.loadPkcs8Base64(reinterpret_cast<const uint8_t*>(dataSet.publicKeyPkcs8.c_str()),
                        dataSet.publicKeyPkcs8.size());
+  BOOST_CHECK_EQUAL(pKey.getKeyType(), KeyType::EC);
 
   OBufferStream os;
   bufferSource("Y2lhbyFob2xhIWhlbGxvIQ==") >> base64Decode() >> streamSink(os);