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Eclipse Ditto is a framework for creating and managing digital twins in the IoT.

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/*
 * Copyright (c) 2021 Contributors to the Eclipse Foundation
 *
 * See the NOTICE file(s) distributed with this work for additional
 * information regarding copyright ownership.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0
 *
 * SPDX-License-Identifier: EPL-2.0
 */

package org.eclipse.ditto.connectivity.service.messaging.signing;

import java.nio.charset.StandardCharsets;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;

import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;

import org.eclipse.ditto.connectivity.model.MessageSendingFailedException;

/**
 * Functional interface for signing a request before sending it.
 *
 * @since 2.1.0
 */
public interface Signing {

    /**
     * Compute HMAC using SHA256 hash function.
     *
     * @param key the key.
     * @param input the message.
     * @return the HMAC.
     */
    static byte[] hmacSha256(final byte[] key, final String input) {
        try {
            final String hmacSha256 = "HmacSHA256";
            final Mac mac = Mac.getInstance(hmacSha256);
            mac.init(new SecretKeySpec(key, hmacSha256));
            return mac.doFinal(input.getBytes(StandardCharsets.UTF_8));
        } catch (final NoSuchAlgorithmException | InvalidKeyException e) {
            throw MessageSendingFailedException.newBuilder()
                    .message("Failed to create a HMAC-SHA256 signature.")
                    .cause(e)
                    .build();
        }
    }

}