/*
 * Copyright 2014 The Netty Project
 *
 * The Netty Project 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 io.netty.handler.ssl.util;

import io.netty.buffer.ByteBufUtil;
import io.netty.buffer.Unpooled;
import io.netty.util.internal.EmptyArrays;
import io.netty.util.concurrent.FastThreadLocal;
import io.netty.util.internal.StringUtil;

import javax.net.ssl.ManagerFactoryParameters;
import javax.net.ssl.TrustManager;
import javax.net.ssl.TrustManagerFactory;
import javax.net.ssl.X509TrustManager;
import java.security.KeyStore;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.cert.CertificateEncodingException;
import java.security.cert.CertificateException;
import java.security.cert.X509Certificate;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.regex.Pattern;

An TrustManagerFactory that trusts an X.509 certificate whose SHA1 checksum matches. 

NOTE: It is recommended to verify certificates and their chain to prevent
Man-in-the-middle attacks. This TrustManagerFactory will only verify that the fingerprint of certificates match one
of the given fingerprints. This procedure is called
certificate pinning and
is an effective protection. For maximum security one should verify that the whole certificate chain is as expected.
It is worth mentioning that certain firewalls, proxies or other appliances found in corporate environments,
actually perform Man-in-the-middle attacks and thus present a different certificate fingerprint.

 The SHA1 checksum of an X.509 certificate is calculated from its DER encoded format. You can get the fingerprint of an X.509 certificate using the openssl command. For example: 
$ openssl x509 -fingerprint -sha1 -in my_certificate.crt
SHA1 Fingerprint=4E:85:10:55:BC:7B:12:08:D1:EA:0A:12:C9:72:EE:F3:AA:B2:C7:CB
-----BEGIN CERTIFICATE-----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==
-----END CERTIFICATE-----


/**
 * An {@link TrustManagerFactory} that trusts an X.509 certificate whose SHA1 checksum matches.
 * <p>
 * <strong>NOTE:</strong> It is recommended to verify certificates and their chain to prevent
 * <a href="https://en.wikipedia.org/wiki/Man-in-the-middle_attack">Man-in-the-middle attacks</a>.
 * This {@link TrustManagerFactory} will <strong>only</strong> verify that the fingerprint of certificates match one
 * of the given fingerprints. This procedure is called
 * <a href="https://en.wikipedia.org/wiki/Transport_Layer_Security#Certificate_pinning">certificate pinning</a> and
 * is an effective protection. For maximum security one should verify that the whole certificate chain is as expected.
 * It is worth mentioning that certain firewalls, proxies or other appliances found in corporate environments,
 * actually perform Man-in-the-middle attacks and thus present a different certificate fingerprint.
 * </p>
 * <p>
 * The SHA1 checksum of an X.509 certificate is calculated from its DER encoded format.  You can get the fingerprint of
 * an X.509 certificate using the {@code openssl} command.  For example:
 *
 * <pre>
 * $ openssl x509 -fingerprint -sha1 -in my_certificate.crt
 * SHA1 Fingerprint=4E:85:10:55:BC:7B:12:08:D1:EA:0A:12:C9:72:EE:F3:AA:B2:C7:CB
 * -----BEGIN CERTIFICATE-----
 * MIIBqjCCAROgAwIBAgIJALiT3Nvp0kvmMA0GCSqGSIb3DQEBBQUAMBYxFDASBgNV
 * BAMTC2V4YW1wbGUuY29tMCAXDTcwMDEwMTAwMDAwMFoYDzk5OTkxMjMxMjM1OTU5
 * WjAWMRQwEgYDVQQDEwtleGFtcGxlLmNvbTCBnzANBgkqhkiG9w0BAQEFAAOBjQAw
 * gYkCgYEAnadvODG0QCiHhaFZlLHtr5gLIkDQS8ErZ//KfqeCHTC/KJsl3xYFk0zG
 * aCv2FcmkOlokm77qV8qOW2DZdND7WuYzX6nLVuLb+GYxZ7b45iMAbAajvGh8jc9U
 * o07fUIahGqTDAIAGCWsoLUOQ9nMzO/8GRHcXJAeQ2MGY2VpCcv0CAwEAATANBgkq
 * hkiG9w0BAQUFAAOBgQBpRCnmjmNM0D7yrpkUJpBTNiqinhKLbeOvPWm+YmdInUUs
 * LoMu0mZ1IANemLwqbwJJ76fknngeB+YuVAj46SurvVCV6ekwHcbgpW1u063IRwKk
 * tQhOBO0HQxldUS4+4MYv/kuvnKkbjfgh5qfWw89Kx4kD+cycpP4yPtgDGk8ZMA==
 * -----END CERTIFICATE-----
 * </pre>
 * </p>
 */
public final class FingerprintTrustManagerFactory extends SimpleTrustManagerFactory {

    private static final Pattern FINGERPRINT_PATTERN = Pattern.compile("^[0-9a-fA-F:]+$");
    private static final Pattern FINGERPRINT_STRIP_PATTERN = Pattern.compile(":");
    private static final int SHA1_BYTE_LEN = 20;
    private static final int SHA1_HEX_LEN = SHA1_BYTE_LEN * 2;

    private static final FastThreadLocal<MessageDigest> tlmd = new FastThreadLocal<MessageDigest>() {
        @Override
        protected MessageDigest initialValue() {
            try {
                return MessageDigest.getInstance("SHA1");
            } catch (NoSuchAlgorithmException e) {
                // All Java implementation must have SHA1 digest algorithm.
                throw new Error(e);
            }
        }
    };

    private final TrustManager tm = new X509TrustManager() {

        @Override
        public void checkClientTrusted(X509Certificate[] chain, String s) throws CertificateException {
            checkTrusted("client", chain);
        }

        @Override
        public void checkServerTrusted(X509Certificate[] chain, String s) throws CertificateException {
            checkTrusted("server", chain);
        }

        private void checkTrusted(String type, X509Certificate[] chain) throws CertificateException {
            X509Certificate cert = chain[0];
            byte[] fingerprint = fingerprint(cert);
            boolean found = false;
            for (byte[] allowedFingerprint: fingerprints) {
                if (Arrays.equals(fingerprint, allowedFingerprint)) {
                    found = true;
                    break;
                }
            }

            if (!found) {
                throw new CertificateException(
                        type + " certificate with unknown fingerprint: " + cert.getSubjectDN());
            }
        }

        private byte[] fingerprint(X509Certificate cert) throws CertificateEncodingException {
            MessageDigest md = tlmd.get();
            md.reset();
            return md.digest(cert.getEncoded());
        }

        @Override
        public X509Certificate[] getAcceptedIssuers() {
            return EmptyArrays.EMPTY_X509_CERTIFICATES;
        }
    };

    private final byte[][] fingerprints;

    
Creates a new instance.
Params:
fingerprints – a list of SHA1 fingerprints in hexadecimal form/**
     * Creates a new instance.
     *
     * @param fingerprints a list of SHA1 fingerprints in hexadecimal form
     */
    public FingerprintTrustManagerFactory(Iterable<String> fingerprints) {
        this(toFingerprintArray(fingerprints));
    }

    
Creates a new instance.
Params:
fingerprints – a list of SHA1 fingerprints in hexadecimal form/**
     * Creates a new instance.
     *
     * @param fingerprints a list of SHA1 fingerprints in hexadecimal form
     */
    public FingerprintTrustManagerFactory(String... fingerprints) {
        this(toFingerprintArray(Arrays.asList(fingerprints)));
    }

    
Creates a new instance.
Params:
fingerprints – a list of SHA1 fingerprints/**
     * Creates a new instance.
     *
     * @param fingerprints a list of SHA1 fingerprints
     */
    public FingerprintTrustManagerFactory(byte[]... fingerprints) {
        if (fingerprints == null) {
            throw new NullPointerException("fingerprints");
        }

        List<byte[]> list = new ArrayList<byte[]>(fingerprints.length);
        for (byte[] f: fingerprints) {
            if (f == null) {
                break;
            }
            if (f.length != SHA1_BYTE_LEN) {
                throw new IllegalArgumentException("malformed fingerprint: " +
                        ByteBufUtil.hexDump(Unpooled.wrappedBuffer(f)) + " (expected: SHA1)");
            }
            list.add(f.clone());
        }

        this.fingerprints = list.toArray(new byte[list.size()][]);
    }

    private static byte[][] toFingerprintArray(Iterable<String> fingerprints) {
        if (fingerprints == null) {
            throw new NullPointerException("fingerprints");
        }

        List<byte[]> list = new ArrayList<byte[]>();
        for (String f: fingerprints) {
            if (f == null) {
                break;
            }

            if (!FINGERPRINT_PATTERN.matcher(f).matches()) {
                throw new IllegalArgumentException("malformed fingerprint: " + f);
            }
            f = FINGERPRINT_STRIP_PATTERN.matcher(f).replaceAll("");
            if (f.length() != SHA1_HEX_LEN) {
                throw new IllegalArgumentException("malformed fingerprint: " + f + " (expected: SHA1)");
            }

            list.add(StringUtil.decodeHexDump(f));
        }

        return list.toArray(new byte[list.size()][]);
    }

    @Override
    protected void engineInit(KeyStore keyStore) throws Exception { }

    @Override
    protected void engineInit(ManagerFactoryParameters managerFactoryParameters) throws Exception { }

    @Override
    protected TrustManager[] engineGetTrustManagers() {
        return new TrustManager[] { tm };
    }
}