convenience method for sole 256, 384, 512 bit key

Author: overheadhunter

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

@@ -100,6 +100,33 @@ interface CtrComputer {
 		byte[] computeCtr(byte[] input, byte[] key, final byte[] iv);
 	}
 
+	/**
+	 * Convenience method using a single 256, 384, or 512 bits key. This is just a wrapper for {@link #encrypt(byte[], byte[], byte[], byte[]...)}.
+	 * @param key Combined key, which is split in half.
+	 * @param plaintext Your plaintext, which shall be encrypted.
+	 * @param associatedData Optional associated data, which gets authenticated but not encrypted.
+	 * @return IV + Ciphertext as a concatenated byte array.
+	 */
+	public byte[] encrypt(SecretKey key, byte[] plaintext, byte[]... associatedData) {
+		final byte[] keyBytes = key.getEncoded();
+		if (keyBytes.length != 64 && keyBytes.length != 48 && keyBytes.length != 32) {
+			throw new IllegalArgumentException("Key length must be 256, 384, or 512 bits.");
+		}
+		final int subkeyLen = keyBytes.length / 2;
+		assert subkeyLen == 32 || subkeyLen == 24 || subkeyLen == 16;
+		final byte[] macKey = new byte[subkeyLen];
+		final byte[] ctrKey = new byte[subkeyLen];
+		try {
+			System.arraycopy(keyBytes, 0, macKey, 0, macKey.length); // K1 = leftmost(K, len(K)/2);
+			System.arraycopy(keyBytes, macKey.length, ctrKey, 0, ctrKey.length); // K2 = rightmost(K, len(K)/2);
+			return encrypt(ctrKey, macKey, plaintext, associatedData);
+		} finally {
+			Arrays.fill(macKey, (byte) 0);
+			Arrays.fill(ctrKey, (byte) 0);
+			Arrays.fill(keyBytes, (byte) 0);
+		}
+	}
+
 	/**
 	 * Convenience method, if you are using the javax.crypto API. This is just a wrapper for {@link #encrypt(byte[], byte[], byte[], byte[]...)}.
 	 *
@@ -150,6 +177,36 @@ public byte[] encrypt(byte[] ctrKey, byte[] macKey, byte[] plaintext, byte[]...
 		return result;
 	}
 
+	/**
+	 * Convenience method using a single 256, 384, or 512 bits key. This is just a wrapper for {@link #decrypt(byte[], byte[], byte[], byte[]...)}.
+	 * @param key Combined key, which is split in half.
+	 * @param ciphertext Your cipehrtext, which shall be decrypted.
+	 * @param associatedData Optional associated data, which gets authenticated but not encrypted.
+	 * @return Plaintext byte array.
+	 * @throws IllegalArgumentException       If keys are invalid.
+	 * @throws UnauthenticCiphertextException If the authentication failed, e.g. because ciphertext and/or associatedData are corrupted.
+	 * @throws IllegalBlockSizeException      If the provided ciphertext is of invalid length.
+	 */
+	public byte[] decrypt(SecretKey key, byte[] ciphertext, byte[]... associatedData) throws UnauthenticCiphertextException, IllegalBlockSizeException {
+		final byte[] keyBytes = key.getEncoded();
+		if (keyBytes.length != 64 && keyBytes.length != 48 && keyBytes.length != 32) {
+			throw new IllegalArgumentException("Key length must be 256, 384, or 512 bits.");
+		}
+		final int subkeyLen = keyBytes.length / 2;
+		assert subkeyLen == 32 || subkeyLen == 24 || subkeyLen == 16;
+		final byte[] macKey = new byte[subkeyLen];
+		final byte[] ctrKey = new byte[subkeyLen];
+		try {
+			System.arraycopy(keyBytes, 0, macKey, 0, macKey.length); // K1 = leftmost(K, len(K)/2);
+			System.arraycopy(keyBytes, macKey.length, ctrKey, 0, ctrKey.length); // K2 = rightmost(K, len(K)/2);
+			return decrypt(ctrKey, macKey, ciphertext, associatedData);
+		} finally {
+			Arrays.fill(macKey, (byte) 0);
+			Arrays.fill(ctrKey, (byte) 0);
+			Arrays.fill(keyBytes, (byte) 0);
+		}
+	}
+
 	/**
 	 * Convenience method, if you are using the javax.crypto API. This is just a wrapper for {@link #decrypt(byte[], byte[], byte[], byte[]...)}.
 	 *

src/test/java/org/cryptomator/siv/SivModeTest.java

@@ -18,6 +18,8 @@
 import org.junit.jupiter.api.DynamicTest;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.TestFactory;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
 import org.mockito.Mockito;
 
 import javax.crypto.IllegalBlockSizeException;
@@ -66,6 +68,17 @@ public void testEncryptWithInvalidKey2() {
 		});
 	}
 
+	@Test
+	public void testEncryptWithInvalidKey3() {
+		SecretKey key = Mockito.mock(SecretKey.class);
+		Mockito.when(key.getEncoded()).thenReturn(new byte[13]);
+
+		SivMode sivMode = new SivMode();
+		Assertions.assertThrows(IllegalArgumentException.class, () -> {
+			sivMode.encrypt(key, new byte[10]);
+		});
+	}
+
 	@Test
 	public void testInvalidCipher1() {
 		BlockCipherFactory factory = () -> null;
@@ -111,6 +124,17 @@ public void testDecryptWithInvalidKey2() {
 		});
 	}
 
+	@Test
+	public void testDecryptWithInvalidKey3() {
+		SecretKey key = Mockito.mock(SecretKey.class);
+		Mockito.when(key.getEncoded()).thenReturn(new byte[13]);
+
+		SivMode sivMode = new SivMode();
+		Assertions.assertThrows(IllegalArgumentException.class, () -> {
+			sivMode.decrypt(key, new byte[10]);
+		});
+	}
+
 	@Test
 	public void testDecryptWithInvalidBlockSize() {
 		final byte[] dummyKey = new byte[16];
@@ -437,9 +461,10 @@ public void testNonceBasedAuthenticatedEncryption() {
 		Assertions.assertArrayEquals(expected, result);
 	}
 
-	@Test
-	public void testEncryptionAndDecryptionUsingJavaxCryptoApi() throws UnauthenticCiphertextException, IllegalBlockSizeException {
-		final byte[] dummyKey = new byte[16];
+	@ParameterizedTest
+	@ValueSource(ints = {16, 24, 32})
+	public void testEncryptionAndDecryptionUsingJavaxCryptoApi(int keylen) throws UnauthenticCiphertextException, IllegalBlockSizeException {
+		final byte[] dummyKey = new byte[keylen];
 		final SecretKey ctrKey = new SecretKeySpec(dummyKey, "AES");
 		final SecretKey macKey = new SecretKeySpec(dummyKey, "AES");
 		final SivMode sivMode = new SivMode();
@@ -449,6 +474,18 @@ public void testEncryptionAndDecryptionUsingJavaxCryptoApi() throws UnauthenticC
 		Assertions.assertArrayEquals(cleartext, decrypted);
 	}
 
+	@ParameterizedTest
+	@ValueSource(ints = {32, 48, 64})
+	public void testEncryptionAndDecryptionUsingSingleJavaxCryptoApi(int keylen) throws UnauthenticCiphertextException, IllegalBlockSizeException {
+		final byte[] dummyKey = new byte[keylen];
+		final SecretKey key = new SecretKeySpec(dummyKey, "AES");
+		final SivMode sivMode = new SivMode();
+		final byte[] cleartext = "hello world".getBytes();
+		final byte[] ciphertext = sivMode.encrypt(key, cleartext);
+		final byte[] decrypted = sivMode.decrypt(key, ciphertext);
+		Assertions.assertArrayEquals(cleartext, decrypted);
+	}
+
 	@Test
 	public void testShiftLeft() {
 		final byte[] output = new byte[4];