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Apache XML Security for Java supports XML-Signature Syntax and Processing, W3C Recommendation 12 February 2002, and XML Encryption Syntax and Processing, W3C Recommendation 10 December 2002. As of version 1.4, the library supports the standard Java API JSR-105: XML Digital Signature APIs.
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/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF licenses this file
 * to you 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 org.apache.xml.security.encryption.params;

import org.apache.xml.security.signature.XMLSignature;
import org.apache.xml.security.utils.EncryptionConstants;

/**
 * Class HKDFParams (HKDF parameter) is used to specify
 * parameters for the HMAC-based Extract-and-Expand Key Derivation Function.
 * @see HMAC-based
 * Extract-and-Expand Key Derivation Function (HKDF)
 */
public class HKDFParams extends KeyDerivationParameters {

    private String hmacHashAlgorithm;
    private byte[] salt;
    private byte[] info;

    /**
     * Constructor HKDFParams with specified digest algorithm.
     *
     * @param keyBitLength the length of the derived key in bits
     * @param hmacHashAlgorithm the HMAC hash algorithm to use for the key derivation
     */
    protected HKDFParams(int keyBitLength, String hmacHashAlgorithm) {
        super(EncryptionConstants.ALGO_ID_KEYDERIVATION_HKDF, keyBitLength);
        this.hmacHashAlgorithm = hmacHashAlgorithm;
    }

    /**
     * Method return the digest algorithm URI. In case of algorithm is not set, the
     * "default" algorithm http://www.w3.org/2001/04/xmldsig-more#hmac-sha256 URI
     * algorithm is returned.
     *
     * @return the hmac algorithm
     */
    public String getHmacHashAlgorithm() {
        return hmacHashAlgorithm == null? XMLSignature.ALGO_ID_MAC_HMAC_SHA256 : hmacHashAlgorithm;
    }

    /**
     * Method set the digest algorithm URI.
     *
     * @param hmacHashAlgorithm the hmac algorithm URI
     */
    public void setHmacHashAlgorithm(String hmacHashAlgorithm) {
        this.hmacHashAlgorithm = hmacHashAlgorithm;
    }

    /**
     * Method return the salt value which is used for the key derivation.
     *
     * @return the salt value
     */
    public byte[] getSalt() {
        return salt;
    }

    /**
     * Method set the salt value which is used for the key derivation.
     *
     * @param salt
     */
    public void setSalt(byte[] salt) {
        this.salt = salt;
    }

    /**
     * Method return the info value which is used for the key derivation.
     *
     * @return the info value
     */
    public byte[] getInfo() {
        return info;
    }

    /**
     * Method set the info value which is used for the key derivation.
     *
     * @param info
     */
    public void setInfo(byte[] info) {
        this.info = info;
    }

    /**
     * Method create a new builder for the HKDFParams.
     * @param keyBitLength the length of the derived key in bits
     * @param hmacHashAlgorithm the HMAC hash algorithm URI to use for the key derivation
     * @return a new builder instance
     */
    public static Builder createBuilder(int keyBitLength, String hmacHashAlgorithm) {
        return new Builder(keyBitLength, hmacHashAlgorithm);
    }

    /**
     * This class is used to create HKDF configuration parameters {@link HKDFParams}.
     * The key length and HMAC hash algorithm are required parameters.
     */
    public static class Builder {
        private final int keyBitLength;
        private final String hmacHashAlgorithm;
        private byte[] salt;
        private byte[] info;

        /**
         * Constructor for the HKDFParams builder. The key bit length and HMAC hash
         * algorithm are required parameters.
         *
         * @param keyBitLength the length of the derived key in bits
         * @param hmacHashAlgorithm the HMAC hash algorithm URI to use for the key derivation
         */
        protected Builder(int keyBitLength, String hmacHashAlgorithm) {
            this.keyBitLength = keyBitLength;
            this.hmacHashAlgorithm = hmacHashAlgorithm;
        }

        /**
         * Set the (optional) salt value which is used for the key derivation.
         * @param salt the hkdf salt value
         * @return the self updated builder instance
         */
        public Builder salt(byte[] salt) {
            this.salt = salt;
            return this;
        }

        /**
         * Set the (optional) info value which is used for the key derivation.
         * @param info the hkdf info value
         * @return the self updated builder instance
         */
        public Builder info(byte[] info) {
            this.info = info;
            return this;
        }

        /**
         * Build the HKDFParams instance with the configured parameters.
         * @return the configured HKDFParams instance
         */
        public HKDFParams build() {
            HKDFParams params = new HKDFParams(keyBitLength, hmacHashAlgorithm);
            params.setSalt(salt);
            params.setInfo(info);
            return params;
        }
    }
}