Added alternative CTR mode from JCE for faster computation.

Author: overheadhunter

src/main/java/org/cryptomator/siv/JceAesCtrComputer.java

@@ -0,0 +1,52 @@
+package org.cryptomator.siv;
+
+import javax.crypto.BadPaddingException;
+import javax.crypto.Cipher;
+import javax.crypto.IllegalBlockSizeException;
+import javax.crypto.NoSuchPaddingException;
+import javax.crypto.spec.IvParameterSpec;
+import javax.crypto.spec.SecretKeySpec;
+import java.security.InvalidAlgorithmParameterException;
+import java.security.InvalidKeyException;
+import java.security.NoSuchAlgorithmException;
+import java.security.Provider;
+
+/**
+ * Performs CTR Mode computations facilitating a cipher returned by JCE's <code>Cipher.getInstance("AES/CTR/NoPadding")</code>.
+ */
+final class JceAesCtrComputer implements SivMode.CtrComputer {
+
+	private final ThreadLocal<Cipher> threadLocalCipher;
+	
+	public JceAesCtrComputer(final Provider jceSecurityProvider) {
+		this.threadLocalCipher = new ThreadLocal<Cipher>(){
+			@Override
+			protected Cipher initialValue() {
+				try {
+					if (jceSecurityProvider == null) {
+						return Cipher.getInstance("AES/CTR/NoPadding");
+					} else {
+						return Cipher.getInstance("AES/CTR/NoPadding", jceSecurityProvider);
+					}
+				} catch (NoSuchAlgorithmException | NoSuchPaddingException e) {
+					throw new IllegalStateException("AES/CTR/NoPadding not available on this platform.", e);
+				}
+			}
+		};
+	}
+
+	@Override
+	public byte[] computeCtr(byte[] input, byte[] key, final byte[] iv) {
+		try {
+			Cipher cipher = threadLocalCipher.get();
+			cipher.init(Cipher.ENCRYPT_MODE, new SecretKeySpec(key, "AES"), new IvParameterSpec(iv));
+			return cipher.doFinal(input);
+		} catch (InvalidKeyException | InvalidAlgorithmParameterException e) {
+			throw new IllegalArgumentException("Key or IV invalid.");
+		} catch (BadPaddingException e) {
+			throw new IllegalStateException("Cipher doesn't require padding.", e);
+		} catch (IllegalBlockSizeException e) {
+			throw new IllegalStateException("Block size irrelevant for stream ciphers.", e);
+		}
+	}
+}

src/main/java/org/cryptomator/siv/SivMode.java

@@ -52,14 +52,7 @@ public SivMode() {
 	 * @see #SivMode(BlockCipherFactory)
 	 */
 	public SivMode(final Provider jceSecurityProvider) {
-		this(new BlockCipherFactory() {
-
-			@Override
-			public BlockCipher create() {
-				return new JceAesBlockCipher(jceSecurityProvider);
-			}
-
-		});
+		this(ThreadLocal.withInitial(() -> new JceAesBlockCipher(jceSecurityProvider)), new JceAesCtrComputer(jceSecurityProvider));
 	}
 
 	/**