Introduce common IKey interface

CHANGELOG.md

@@ -21,6 +21,7 @@ _Code:_
   - JNI libraries are now available as `libthemis-jni` packages for supported Linux systems ([#552](https://github.com/cossacklabs/themis/pull/552), [#553](https://github.com/cossacklabs/themis/pull/553)).
   - Fixed a NullPointerException bug in `SecureSocket` initialisation ([#557](https://github.com/cossacklabs/themis/pull/557)).
   - Some Themis exceptions have been converted from checked `Exception` to _unchecked_ `RuntimeException`, relaxing requirements for `throws` specifiers ([#563](https://github.com/cossacklabs/themis/pull/563)).
+  - Introduced `IKey` interface with accessors to raw key data ([#564](https://github.com/cossacklabs/themis/pull/564)).
 
 - **Python**
 

src/wrappers/themis/java/com/cossacklabs/themis/AsymmetricKey.java

@@ -19,26 +19,20 @@
 /**
  * Base class for Themis asymmetric keys
  */
-public abstract class AsymmetricKey {
-	
+public abstract class AsymmetricKey extends KeyBytes {
+
 	public static final int KEYTYPE_EC = 0;
 	public static final int KEYTYPE_RSA = 1;
-
-	byte[] key;
 
 	/**
-	 * Creates asymmetric key from byte array
-	 * @param [in] key
+	 * Creates asymmetric key from byte array.
+	 *
+	 * @param key byte array
+	 *
+	 * @throws NullArgumentException if `key` is null.
+	 * @throws InvalidArgumentException if `key` is empty.
 	 */
 	public AsymmetricKey(byte[] key) {
-		this.key = key;
-	}
-
-	/**
-	 * Serializes this key to a byte array
-	 * @return key as byte array
-	 */
-	public byte[] toByteArray() {
-		return key.clone();
+		super(key);
 	}
 }

src/wrappers/themis/java/com/cossacklabs/themis/IKey.java

@@ -0,0 +1,30 @@
+/*
+ * Copyright (c) 2019 Cossack Labs Limited
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.cossacklabs.themis;
+
+/**
+ * Cryptographic key.
+ */
+public interface IKey {
+
+    /**
+     * Serializes this key to a byte array.
+     *
+     * @return key as byte array.
+     */
+    public byte[] toByteArray();
+}

src/wrappers/themis/java/com/cossacklabs/themis/KeyBytes.java

@@ -0,0 +1,50 @@
+/*
+ * Copyright (c) 2019 Cossack Labs Limited
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.cossacklabs.themis;
+
+/**
+ * Key byte storage.
+ */
+abstract class KeyBytes implements IKey {
+
+    final byte[] key;
+
+    /**
+     * Creates a new key from byte array.
+     *
+     * @param key byte array
+     *
+     * @throws NullArgumentException if `key` is null.
+     * @throws InvalidArgumentException if `key` is empty.
+     */
+    public KeyBytes(byte[] key) {
+        if (key == null) {
+            throw new NullArgumentException("key cannot be null");
+        }
+        if (key.length == 0) {
+            throw new InvalidArgumentException("key cannot be empty");
+        }
+        this.key = key;
+    }
+
+    @Override
+    public byte[] toByteArray() {
+        // Java arrays are always mutable. Return a copy to the caller
+        // so that their modifications do not affect the actual key.
+        return this.key.clone();
+    }
+}

src/wrappers/themis/java/com/cossacklabs/themis/PrivateKey.java

@@ -22,13 +22,15 @@
 public class PrivateKey extends AsymmetricKey {
 
 	/**
-	 * Creates new private key from byte array
+	 * Creates private key from byte array.
+	 *
 	 * @param key byte array
+	 *
+	 * @throws NullArgumentException if `key` is null.
+	 * @throws InvalidArgumentException if `key` is empty.
 	 */
 	public PrivateKey(byte[] key) {
-
 		super(key);
-
 	}
 
 }

src/wrappers/themis/java/com/cossacklabs/themis/PublicKey.java

@@ -22,13 +22,15 @@
 public class PublicKey extends AsymmetricKey {
 
 	/**
-	 * Creates new public key from byte array
+	 * Creates public key from byte array.
+	 *
 	 * @param key byte array
+	 *
+	 * @throws NullArgumentException if `key` is null.
+	 * @throws InvalidArgumentException if `key` is empty.
 	 */
 	public PublicKey(byte[] key) {
-
 		super(key);
-
 	}
 
 }