Use the BouncyCastleProvider class directly (#84)

* 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: #68

* Add BouncyCastleConfiguration class for handling BC init

This moves the BouncyCastleProvider creation from CryptoAlgorithm to
BouncyCastleConfiguration, which also contains a static field for classes that
must use a pegged version of BouncyCastle. A newInstance reference is included
from CryptoAlgorithm to BouncyCastleConfiguration to force initialization, since
it depends on BouncyCastle being on the SecurityProvider chain.

* Add comments, and use static method to force class loading

This adds documentation for the purpose of the BouncyCastleConfiguration class,
and uses a static method call to force the BouncyCastleConfiguration class to be
loaded.

src/main/java/com/amazonaws/encryptionsdk/CryptoAlgorithm.java

@@ -16,7 +16,6 @@
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
 import java.security.InvalidKeyException;
-import java.security.Provider;
 import java.security.Security;
 import java.util.EnumSet;
 import java.util.HashMap;
@@ -25,6 +24,7 @@
 import javax.crypto.SecretKey;
 import javax.crypto.spec.SecretKeySpec;
 
+import com.amazonaws.encryptionsdk.internal.BouncyCastleConfiguration;
 import org.bouncycastle.crypto.Digest;
 import org.bouncycastle.crypto.digests.SHA256Digest;
 import org.bouncycastle.crypto.digests.SHA384Digest;
@@ -33,6 +33,7 @@
 
 import com.amazonaws.encryptionsdk.internal.Constants;
 import com.amazonaws.encryptionsdk.model.CiphertextHeaders;
+import org.bouncycastle.jce.provider.BouncyCastleProvider;
 
 /**
  * Describes the cryptographic algorithms available for use in this library.
@@ -103,14 +104,12 @@ public enum CryptoAlgorithm {
     private final int dataKeyLen_;
     private final boolean safeToCache_;
 
+    /**
+     * This block is used to ensure static blocks of BouncyCastleConfiguration are evaluated as a dependency of
+     * the CryptoAlgorithm class
+     */
     static {
-        try {
-            Security.addProvider((Provider)
-                    Class.forName("org.bouncycastle.jce.provider.BouncyCastleProvider").newInstance());
-        } catch (final Throwable ex) {
-            // Swallow this error. We'll either succeed or fail later with reasonable
-            // stacktraces.
-        }
+        BouncyCastleConfiguration.init();
     }
 
     /*

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

@@ -0,0 +1,37 @@
+package com.amazonaws.encryptionsdk.internal;
+
+import org.bouncycastle.jce.provider.BouncyCastleProvider;
+
+import java.security.Security;
+
+/**
+ * This API is internal and subject to change. It is used to add BouncyCastleProvider to the
+ * java.security.Provider list, and to provide a static reference to BouncyCastleProvider for internal
+ * classes.
+ */
+public class BouncyCastleConfiguration {
+    static final BouncyCastleProvider INTERNAL_BOUNCY_CASTLE_PROVIDER;
+    static {
+        BouncyCastleProvider bouncyCastleProvider;
+        try {
+            bouncyCastleProvider = new BouncyCastleProvider();
+            Security.addProvider(bouncyCastleProvider);
+        } catch (final Throwable ex) {
+            bouncyCastleProvider = null;
+            // Swallow this error. We'll either succeed or fail later with reasonable
+            // stacktraces.
+        }
+        INTERNAL_BOUNCY_CASTLE_PROVIDER = bouncyCastleProvider;
+    }
+
+    /**
+     * Prevent instantiation
+     */
+    private BouncyCastleConfiguration() {
+    }
+
+    /**
+     * No-op used to force class loading on first call, which will cause the static blocks to be executed
+     */
+    public static void init() {}
+}

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

@@ -18,12 +18,15 @@
 
 import com.amazonaws.encryptionsdk.CryptoAlgorithm;
 
+import static com.amazonaws.encryptionsdk.internal.BouncyCastleConfiguration.INTERNAL_BOUNCY_CASTLE_PROVIDER;
+
 /**
  * Provides a consistent interface across various trailing signature algorithms.
  *
  * NOTE: This is not a stable API and may undergo breaking changes in the future.
  */
 public abstract class TrailingSignatureAlgorithm {
+
     private TrailingSignatureAlgorithm() {
         /* Do not allow arbitrary subclasses */
     }
@@ -84,7 +87,7 @@ public String serializePublicKey(PublicKey key) {
 
         @Override
         public KeyPair generateKey() throws GeneralSecurityException {
-            KeyPairGenerator keyGen = KeyPairGenerator.getInstance("ECDSA", "BC");
+            KeyPairGenerator keyGen = KeyPairGenerator.getInstance("ECDSA", INTERNAL_BOUNCY_CASTLE_PROVIDER);
             keyGen.initialize(ecSpec, Utils.getSecureRandom());
 
             return keyGen.generateKeyPair();