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/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the "Elastic License
 * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
 * Public License v 1"; you may not use this file except in compliance with, at
 * your election, the "Elastic License 2.0", the "GNU Affero General Public
 * License v3.0 only", or the "Server Side Public License, v 1".
 */

package org.elasticsearch.common.ssl;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.cert.CertificateEncodingException;
import java.security.cert.X509Certificate;
import java.util.Objects;

public final class SslUtil {

    private SslUtil() {
        // utility class
    }

    public static String calculateFingerprint(X509Certificate certificate, String algorithm) throws CertificateEncodingException {
        final MessageDigest sha1 = messageDigest(algorithm);
        sha1.update(certificate.getEncoded());
        return toHexString(sha1.digest());
    }

    static MessageDigest messageDigest(String digestAlgorithm) {
        try {
            return MessageDigest.getInstance(digestAlgorithm);
        } catch (NoSuchAlgorithmException e) {
            throw new SslConfigException("unexpected exception creating MessageDigest instance for [" + digestAlgorithm + "]", e);
        }
    }

    private static final char[] HEX_DIGITS = "0123456789abcdef".toCharArray();

    /**
     * Format a byte array as a hex string.
     *
     * @param bytes the input to be represented as hex.
     * @return a hex representation of the input as a String.
     */
    static String toHexString(byte[] bytes) {
        return new String(toHexCharArray(bytes));
    }

    /**
     * Encodes the byte array into a newly created hex char array, without allocating any other temporary variables.
     *
     * @param bytes the input to be encoded as hex.
     * @return the hex encoding of the input as a char array.
     */
    static char[] toHexCharArray(byte[] bytes) {
        Objects.requireNonNull(bytes);
        final char[] result = new char[2 * bytes.length];
        for (int i = 0; i < bytes.length; i++) {
            byte b = bytes[i];
            result[2 * i] = HEX_DIGITS[b >> 4 & 0xf];
            result[2 * i + 1] = HEX_DIGITS[b & 0xf];
        }
        return result;
    }

}