Use the BouncyCastleProvider class directly

This avoids issues where a shaded version of BCProvider is installed in the
system JCE provider list, which can result in problems when we pass an
ECNamedCurveParameterSpec from a different shaded version of BC.

Fixes: aws#68

src/main/java/com/amazonaws/encryptionsdk/internal/TrailingSignatureAlgorithm.java

@@ -24,6 +24,8 @@
  * NOTE: This is not a stable API and may undergo breaking changes in the future.
  */
 public abstract class TrailingSignatureAlgorithm {
+    private static final BouncyCastleProvider BC_PROVIDER = new BouncyCastleProvider();
+
     private TrailingSignatureAlgorithm() {
         /* Do not allow arbitrary subclasses */
     }
@@ -84,7 +86,7 @@ public String serializePublicKey(PublicKey key) {
 
         @Override
         public KeyPair generateKey() throws GeneralSecurityException {
-            KeyPairGenerator keyGen = KeyPairGenerator.getInstance("ECDSA", "BC");
+            KeyPairGenerator keyGen = KeyPairGenerator.getInstance("ECDSA", BC_PROVIDER);
             keyGen.initialize(ecSpec, Utils.getSecureRandom());
 
             return keyGen.generateKeyPair();