src/java.base/share/classes/sun/security/ssl/CertificateVerify.java

/*
 * Copyright (c) 2015, 2025, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package sun.security.ssl;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.security.*;
import java.text.MessageFormat;
import java.util.Arrays;
import java.util.Locale;
import java.util.Map;

import sun.security.ssl.SSLHandshake.HandshakeMessage;
import sun.security.ssl.X509Authentication.X509Credentials;
import sun.security.ssl.X509Authentication.X509Possession;
import sun.security.util.HexDumpEncoder;

/**
 * Pack of the CertificateVerify handshake message.
 */
final class CertificateVerify {
    static final SSLConsumer s30HandshakeConsumer =
        new S30CertificateVerifyConsumer();
    static final HandshakeProducer s30HandshakeProducer =
        new S30CertificateVerifyProducer();

    static final SSLConsumer t10HandshakeConsumer =
        new T10CertificateVerifyConsumer();
    static final HandshakeProducer t10HandshakeProducer =
        new T10CertificateVerifyProducer();

    static final SSLConsumer t12HandshakeConsumer =
        new T12CertificateVerifyConsumer();
    static final HandshakeProducer t12HandshakeProducer =
        new T12CertificateVerifyProducer();

    static final SSLConsumer t13HandshakeConsumer =
        new T13CertificateVerifyConsumer();
    static final HandshakeProducer t13HandshakeProducer =
        new T13CertificateVerifyProducer();

    /**
     * The CertificateVerify handshake message (SSL 3.0).
     */
    static final class S30CertificateVerifyMessage extends HandshakeMessage {
        // signature bytes
        private final byte[] signature;

        S30CertificateVerifyMessage(HandshakeContext context,
                X509Possession x509Possession) throws IOException {
            super(context);

            // This happens in client side only.
            ClientHandshakeContext chc = (ClientHandshakeContext)context;
            byte[] temporary;
            String algorithm = x509Possession.popPrivateKey.getAlgorithm();
            try {
                Signature signer =
                        getSignature(algorithm, x509Possession.popPrivateKey);
                byte[] hashes = chc.handshakeHash.digest(algorithm,
                        chc.handshakeSession.getMasterSecret());
                signer.update(hashes);
                temporary = signer.sign();
            } catch (NoSuchAlgorithmException nsae) {
                throw chc.conContext.fatal(Alert.INTERNAL_ERROR,
                        "Unsupported signature algorithm (" + algorithm +
                        ") used in CertificateVerify handshake message", nsae);
            } catch (GeneralSecurityException gse) {
                throw chc.conContext.fatal(Alert.HANDSHAKE_FAILURE,
                        "Cannot produce CertificateVerify signature", gse);
            }

            this.signature = temporary;
        }

        S30CertificateVerifyMessage(HandshakeContext context,
                ByteBuffer m) throws IOException {
            super(context);

            // This happens in server side only.
            ServerHandshakeContext shc = (ServerHandshakeContext)context;

            //  digitally-signed struct {
            //    select(SignatureAlgorithm) {
            //        case anonymous: struct { };
            //        case rsa:
            //            opaque md5_hash[16];
            //            opaque sha_hash[20];
            //        case dsa:
            //            opaque sha_hash[20];
            //    };
            //  } Signature;
            if (m.remaining() < 2) {
                throw shc.conContext.fatal(Alert.ILLEGAL_PARAMETER,
                    "Invalid CertificateVerify message: no sufficient data");
            }

            // read and verify the signature
            this.signature = Record.getBytes16(m);
            X509Credentials x509Credentials = null;
            for (SSLCredentials cd : shc.handshakeCredentials) {
                if (cd instanceof X509Credentials) {
                    x509Credentials = (X509Credentials)cd;
                    break;
                }
            }

            if (x509Credentials == null ||
                    x509Credentials.popPublicKey == null) {
                throw shc.conContext.fatal(Alert.HANDSHAKE_FAILURE,
                    "No X509 credentials negotiated for CertificateVerify");
            }

            String algorithm = x509Credentials.popPublicKey.getAlgorithm();
            try {
                Signature signer =
                        getSignature(algorithm, x509Credentials.popPublicKey);
                byte[] hashes = shc.handshakeHash.digest(algorithm,
                        shc.handshakeSession.getMasterSecret());
                signer.update(hashes);
                if (!signer.verify(signature)) {
                    throw shc.conContext.fatal(Alert.HANDSHAKE_FAILURE,
                        "Invalid CertificateVerify message: invalid signature");
                }
            } catch (NoSuchAlgorithmException nsae) {
                throw shc.conContext.fatal(Alert.INTERNAL_ERROR,
                        "Unsupported signature algorithm (" + algorithm +
                        ") used in CertificateVerify handshake message", nsae);
            } catch (GeneralSecurityException gse) {
                throw shc.conContext.fatal(Alert.HANDSHAKE_FAILURE,
                        "Cannot verify CertificateVerify signature", gse);
            }
        }

        @Override
        public SSLHandshake handshakeType() {
            return SSLHandshake.CERTIFICATE_VERIFY;
        }

        @Override
        public int messageLength() {
            return 2 + signature.length;    //  2: length of signature
        }

        @Override
        public void send(HandshakeOutStream hos) throws IOException {
            hos.putBytes16(signature);
        }

        @Override
        public String toString() {
            MessageFormat messageFormat = new MessageFormat(
                    """
                            "CertificateVerify": '{'
                              "signature": '{'
                            {0}
                              '}'
                            '}'""",
                    Locale.ENGLISH);

            HexDumpEncoder hexEncoder = new HexDumpEncoder();
            Object[] messageFields = {
                Utilities.indent(
                        hexEncoder.encodeBuffer(signature), "    ")
            };

            return messageFormat.format(messageFields);
        }

        /*
         * Get the Signature object appropriate for verification using the
         * given signature algorithm.
         */
        private static Signature getSignature(String algorithm,
                Key key) throws GeneralSecurityException {
            Signature signer;
            switch (algorithm) {
                case "RSA":
                    signer = Signature.getInstance(JsseJce.SIGNATURE_RAWRSA);
                    break;
                case "DSA":
                    signer = Signature.getInstance(JsseJce.SIGNATURE_RAWDSA);
                    break;
                case "EC":
                    signer = Signature.getInstance(JsseJce.SIGNATURE_RAWECDSA);
                    break;
                default:
                    throw new SignatureException("Unrecognized algorithm: "
                        + algorithm);
            }

            if (key instanceof PublicKey) {
                signer.initVerify((PublicKey)(key));
            } else {
                signer.initSign((PrivateKey)key);
            }

            return signer;
        }
    }

    /**
     * The "CertificateVerify" handshake message producer.
     */
    private static final
            class S30CertificateVerifyProducer implements HandshakeProducer {
        // Prevent instantiation of this class.
        private S30CertificateVerifyProducer() {
            // blank
        }

        @Override
        public byte[] produce(ConnectionContext context,
                HandshakeMessage message) throws IOException {
            // The producing happens in client side only.
            ClientHandshakeContext chc = (ClientHandshakeContext)context;

            X509Possession x509Possession = null;
            for (SSLPossession possession : chc.handshakePossessions) {
                if (possession instanceof X509Possession) {
                    x509Possession = (X509Possession)possession;
                    break;
                }
            }

            if (x509Possession == null ||
                    x509Possession.popPrivateKey == null) {
                if (SSLLogger.isOn && SSLLogger.isOn("ssl,handshake")) {
                    SSLLogger.fine(
                        "No X.509 credentials negotiated for CertificateVerify");
                }

                return null;
            }

            S30CertificateVerifyMessage cvm =
                    new S30CertificateVerifyMessage(chc, x509Possession);
            if (SSLLogger.isOn && SSLLogger.isOn("ssl,handshake")) {
                SSLLogger.fine(
                        "Produced CertificateVerify handshake message", cvm);
            }

            // Output the handshake message.
            cvm.write(chc.handshakeOutput);
            chc.handshakeOutput.flush();

            // The handshake message has been delivered.
            return null;
        }
    }

    /**
     * The "CertificateVerify" handshake message consumer.
     */
    private static final
            class S30CertificateVerifyConsumer implements SSLConsumer {
        // Prevent instantiation of this class.
        private S30CertificateVerifyConsumer() {
            // blank
        }

        @Override
        public void consume(ConnectionContext context,
                ByteBuffer message) throws IOException {
            // The consuming happens in server side only.
            ServerHandshakeContext shc = (ServerHandshakeContext)context;

            // Clean up this consumer
            shc.handshakeConsumers.remove(SSLHandshake.CERTIFICATE_VERIFY.id);

            // Ensure that the CV message follows the CKE
            if (shc.handshakeConsumers.containsKey(
                    SSLHandshake.CLIENT_KEY_EXCHANGE.id)) {
                throw shc.conContext.fatal(Alert.UNEXPECTED_MESSAGE,
                        "Unexpected CertificateVerify handshake message");
            }

            S30CertificateVerifyMessage cvm =
                    new S30CertificateVerifyMessage(shc, message);
            if (SSLLogger.isOn && SSLLogger.isOn("ssl,handshake")) {
                SSLLogger.fine(
                    "Consuming CertificateVerify handshake message", cvm);
            }

            //
            // update
            //
            // Need no additional validation.

            //
            // produce
            //
            // Need no new handshake message producers here.
        }
    }

    /**
     * The CertificateVerify handshake message (TLS 1.0/1.1).
     */
    static final class T10CertificateVerifyMessage extends HandshakeMessage {
        // signature bytes
        private final byte[] signature;

        T10CertificateVerifyMessage(HandshakeContext context,
                X509Possession x509Possession) throws IOException {
            super(context);

            // This happens in client side only.
            ClientHandshakeContext chc = (ClientHandshakeContext)context;
            byte[] temporary;
            String algorithm = x509Possession.popPrivateKey.getAlgorithm();
            try {
                Signature signer =
                        getSignature(algorithm, x509Possession.popPrivateKey);
                byte[] hashes = chc.handshakeHash.digest(algorithm);
                signer.update(hashes);
                temporary = signer.sign();
            } catch (NoSuchAlgorithmException nsae) {
                throw chc.conContext.fatal(Alert.INTERNAL_ERROR,
                        "Unsupported signature algorithm (" + algorithm +
                        ") used in CertificateVerify handshake message", nsae);
            } catch (GeneralSecurityException gse) {
                throw chc.conContext.fatal(Alert.HANDSHAKE_FAILURE,
                    "Cannot produce CertificateVerify signature", gse);
            }

            this.signature = temporary;
        }

        T10CertificateVerifyMessage(HandshakeContext context,
                ByteBuffer m) throws IOException {
            super(context);

            // This happens in server side only.
            ServerHandshakeContext shc = (ServerHandshakeContext)context;

            //  digitally-signed struct {
            //    select(SignatureAlgorithm) {
            //        case anonymous: struct { };
            //        case rsa:
            //            opaque md5_hash[16];
            //            opaque sha_hash[20];
            //        case dsa:
            //            opaque sha_hash[20];
            //    };
            //  } Signature;
            if (m.remaining() < 2) {
                throw shc.conContext.fatal(Alert.ILLEGAL_PARAMETER,
                    "Invalid CertificateVerify message: no sufficient data");
            }

            // read and verify the signature
            this.signature = Record.getBytes16(m);
            X509Credentials x509Credentials = null;
            for (SSLCredentials cd : shc.handshakeCredentials) {
                if (cd instanceof X509Credentials) {
                    x509Credentials = (X509Credentials)cd;
                    break;
                }
            }

            if (x509Credentials == null ||
                    x509Credentials.popPublicKey == null) {
                throw shc.conContext.fatal(Alert.HANDSHAKE_FAILURE,
                    "No X509 credentials negotiated for CertificateVerify");
            }

            String algorithm = x509Credentials.popPublicKey.getAlgorithm();
            try {
                Signature signer =
                        getSignature(algorithm, x509Credentials.popPublicKey);
                byte[] hashes = shc.handshakeHash.digest(algorithm);
                signer.update(hashes);
                if (!signer.verify(signature)) {
                    throw shc.conContext.fatal(Alert.HANDSHAKE_FAILURE,
                        "Invalid CertificateVerify message: invalid signature");
                }
            } catch (NoSuchAlgorithmException nsae) {
                throw shc.conContext.fatal(Alert.INTERNAL_ERROR,
                        "Unsupported signature algorithm (" + algorithm +
                        ") used in CertificateVerify handshake message", nsae);
            } catch (GeneralSecurityException gse) {
                throw shc.conContext.fatal(Alert.HANDSHAKE_FAILURE,
                        "Cannot verify CertificateVerify signature", gse);
            }
        }

        @Override
        public SSLHandshake handshakeType() {
            return SSLHandshake.CERTIFICATE_VERIFY;
        }

        @Override
        public int messageLength() {
            return 2 + signature.length;    //  2: length of signature
        }

        @Override
        public void send(HandshakeOutStream hos) throws IOException {
            hos.putBytes16(signature);
        }

        @Override
        public String toString() {
            MessageFormat messageFormat = new MessageFormat(
                    """
                            "CertificateVerify": '{'
                              "signature": '{'
                            {0}
                              '}'
                            '}'""",
                    Locale.ENGLISH);

            HexDumpEncoder hexEncoder = new HexDumpEncoder();
            Object[] messageFields = {
                Utilities.indent(
                        hexEncoder.encodeBuffer(signature), "    ")
            };

            return messageFormat.format(messageFields);
        }

        /*
         * Get the Signature object appropriate for verification using the
         * given signature algorithm.
         */
        private static Signature getSignature(String algorithm,
                Key key) throws GeneralSecurityException {
            Signature signer;
            switch (algorithm) {
                case "RSA":
                    signer = Signature.getInstance(JsseJce.SIGNATURE_RAWRSA);
                    break;
                case "DSA":
                    signer = Signature.getInstance(JsseJce.SIGNATURE_RAWDSA);
                    break;
                case "EC":
                    signer = Signature.getInstance(JsseJce.SIGNATURE_RAWECDSA);
                    break;
                case "EdDSA":
                    signer = Signature.getInstance(JsseJce.SIGNATURE_EDDSA);
                    break;
                default:
                    throw new SignatureException("Unrecognized algorithm: "
                        + algorithm);
            }

            if (key instanceof PublicKey) {
                signer.initVerify((PublicKey)(key));
            } else {
                signer.initSign((PrivateKey)key);
            }

            return signer;
        }
    }

    /**
     * The "CertificateVerify" handshake message producer.
     */
    private static final
            class T10CertificateVerifyProducer implements HandshakeProducer {
        // Prevent instantiation of this class.
        private T10CertificateVerifyProducer() {
            // blank
        }

        @Override
        public byte[] produce(ConnectionContext context,
                HandshakeMessage message) throws IOException {
            // The producing happens in client side only.
            ClientHandshakeContext chc = (ClientHandshakeContext)context;
            X509Possession x509Possession = null;
            for (SSLPossession possession : chc.handshakePossessions) {
                if (possession instanceof X509Possession) {
                    x509Possession = (X509Possession)possession;
                    break;
                }
            }

            if (x509Possession == null ||
                    x509Possession.popPrivateKey == null) {
                if (SSLLogger.isOn && SSLLogger.isOn("ssl,handshake")) {
                    SSLLogger.fine(
                        "No X.509 credentials negotiated for CertificateVerify");
                }

                return null;
            }

            T10CertificateVerifyMessage cvm =
                    new T10CertificateVerifyMessage(chc, x509Possession);
            if (SSLLogger.isOn && SSLLogger.isOn("ssl,handshake")) {
                SSLLogger.fine(
                        "Produced CertificateVerify handshake message", cvm);
            }

            // Output the handshake message.
            cvm.write(chc.handshakeOutput);
            chc.handshakeOutput.flush();

            // The handshake message has been delivered.
            return null;
        }
    }

    /**
     * The "CertificateVerify" handshake message consumer.
     */
    private static final
            class T10CertificateVerifyConsumer implements SSLConsumer {
        // Prevent instantiation of this class.
        private T10CertificateVerifyConsumer() {
            // blank
        }

        @Override
        public void consume(ConnectionContext context,
                ByteBuffer message) throws IOException {
            // The consuming happens in server side only.
            ServerHandshakeContext shc = (ServerHandshakeContext)context;

            // Clean up this consumer
            shc.handshakeConsumers.remove(SSLHandshake.CERTIFICATE_VERIFY.id);

            // Ensure that the CV message follows the CKE
            if (shc.handshakeConsumers.containsKey(
                    SSLHandshake.CLIENT_KEY_EXCHANGE.id)) {
                throw shc.conContext.fatal(Alert.UNEXPECTED_MESSAGE,
                        "Unexpected CertificateVerify handshake message");
            }

            T10CertificateVerifyMessage cvm =
                    new T10CertificateVerifyMessage(shc, message);
            if (SSLLogger.isOn && SSLLogger.isOn("ssl,handshake")) {
                SSLLogger.fine(
                        "Consuming CertificateVerify handshake message", cvm);
            }

            //
            // update
            //
            // Need no additional validation.

            //
            // produce
            //
            // Need no new handshake message producers here.        }
        }
    }

    /**
     * The CertificateVerify handshake message (TLS 1.2).
     */
    static final class T12CertificateVerifyMessage extends HandshakeMessage {
        // the signature algorithm
        private final SignatureScheme signatureScheme;

        // signature bytes
        private final byte[] signature;

        T12CertificateVerifyMessage(HandshakeContext context,
                X509Possession x509Possession) throws IOException {
            super(context);

            // This happens in client side only.
            ClientHandshakeContext chc = (ClientHandshakeContext)context;
            Map.Entry<SignatureScheme, Signature> schemeAndSigner =
                    SignatureScheme.getSignerOfPreferableAlgorithm(
                    chc.sslConfig,
                    chc.algorithmConstraints,
                    chc.peerRequestedSignatureSchemes,
                    x509Possession,
                    chc.negotiatedProtocol);
            if (schemeAndSigner == null) {
                // Unlikely, the credential's generator should have
                // selected the preferable signature algorithm properly.
                throw chc.conContext.fatal(Alert.INTERNAL_ERROR,
                    "No supported CertificateVerify signature algorithm for " +
                    x509Possession.popPrivateKey.getAlgorithm() +
                    "  key");
            }

            this.signatureScheme = schemeAndSigner.getKey();
            byte[] temporary;
            try {
                Signature signer = schemeAndSigner.getValue();
                signer.update(chc.handshakeHash.archived());
                temporary = signer.sign();
            } catch (SignatureException ikse) {
                throw chc.conContext.fatal(Alert.HANDSHAKE_FAILURE,
                        "Cannot produce CertificateVerify signature", ikse);
            }

            this.signature = temporary;
        }

        T12CertificateVerifyMessage(HandshakeContext handshakeContext,
                ByteBuffer m) throws IOException {
            super(handshakeContext);

            // This happens in server side only.
            ServerHandshakeContext shc =
                    (ServerHandshakeContext)handshakeContext;

            // struct {
            //     SignatureAndHashAlgorithm algorithm;
            //     opaque signature<0..2^16-1>;
            // } DigitallySigned;
            if (m.remaining() < 4) {
                throw shc.conContext.fatal(Alert.ILLEGAL_PARAMETER,
                    "Invalid CertificateVerify message: no sufficient data");
            }

            // SignatureAndHashAlgorithm algorithm
            int ssid = Record.getInt16(m);
            this.signatureScheme = SignatureScheme.valueOf(ssid);
            if (signatureScheme == null) {
                throw shc.conContext.fatal(Alert.HANDSHAKE_FAILURE,
                        "Invalid signature algorithm (" + ssid +
                        ") used in CertificateVerify handshake message");
            }

            if (!shc.localSupportedSignAlgs.contains(signatureScheme)) {
                throw shc.conContext.fatal(Alert.HANDSHAKE_FAILURE,
                        "Unsupported signature algorithm (" +
                        signatureScheme.name +
                        ") used in CertificateVerify handshake message");
            }

            // read and verify the signature
            X509Credentials x509Credentials = null;
            for (SSLCredentials cd : shc.handshakeCredentials) {
                if (cd instanceof X509Credentials) {
                    x509Credentials = (X509Credentials)cd;
                    break;
                }
            }

            if (x509Credentials == null ||
                    x509Credentials.popPublicKey == null) {
                throw shc.conContext.fatal(Alert.HANDSHAKE_FAILURE,
                    "No X509 credentials negotiated for CertificateVerify");
            }

            // opaque signature<0..2^16-1>;
            this.signature = Record.getBytes16(m);
            try {
                Signature signer =
                    signatureScheme.getVerifier(x509Credentials.popPublicKey);
                signer.update(shc.handshakeHash.archived());
                if (!signer.verify(signature)) {
                    throw shc.conContext.fatal(Alert.HANDSHAKE_FAILURE,
                        "Invalid CertificateVerify signature");
                }
            } catch (NoSuchAlgorithmException |
                    InvalidAlgorithmParameterException nsae) {
                throw shc.conContext.fatal(Alert.INTERNAL_ERROR,
                        "Unsupported signature algorithm (" +
                        signatureScheme.name +
                        ") used in CertificateVerify handshake message", nsae);
            } catch (InvalidKeyException | SignatureException ikse) {
                throw shc.conContext.fatal(Alert.HANDSHAKE_FAILURE,
                        "Cannot verify CertificateVerify signature", ikse);
            }
        }

        @Override
        public SSLHandshake handshakeType() {
            return SSLHandshake.CERTIFICATE_VERIFY;
        }

        @Override
        public int messageLength() {
            return 4 + signature.length;    //  2: signature algorithm
                                            // +2: length of signature
        }

        @Override
        public void send(HandshakeOutStream hos) throws IOException {
            hos.putInt16(signatureScheme.id);
            hos.putBytes16(signature);
        }

        @Override
        public String toString() {
            MessageFormat messageFormat = new MessageFormat(
                    """
                            "CertificateVerify": '{'
                              "signature algorithm": {0}
                              "signature": '{'
                            {1}
                              '}'
                            '}'""",
                    Locale.ENGLISH);

            HexDumpEncoder hexEncoder = new HexDumpEncoder();
            Object[] messageFields = {
                signatureScheme.name,
                Utilities.indent(
                        hexEncoder.encodeBuffer(signature), "    ")
            };

            return messageFormat.format(messageFields);
        }
    }

    /**
     * The "CertificateVerify" handshake message producer.
     */
    private static final
            class T12CertificateVerifyProducer implements HandshakeProducer {
        // Prevent instantiation of this class.
        private T12CertificateVerifyProducer() {
            // blank
        }

        @Override
        public byte[] produce(ConnectionContext context,
                HandshakeMessage message) throws IOException {
            // The producing happens in client side only.
            ClientHandshakeContext chc = (ClientHandshakeContext)context;

            X509Possession x509Possession = null;
            for (SSLPossession possession : chc.handshakePossessions) {
                if (possession instanceof X509Possession) {
                    x509Possession = (X509Possession)possession;
                    break;
                }
            }

            if (x509Possession == null ||
                    x509Possession.popPrivateKey == null) {
                if (SSLLogger.isOn && SSLLogger.isOn("ssl,handshake")) {
                    SSLLogger.fine(
                        "No X.509 credentials negotiated for CertificateVerify");
                }

                return null;
            }

            T12CertificateVerifyMessage cvm =
                    new T12CertificateVerifyMessage(chc, x509Possession);
            if (SSLLogger.isOn && SSLLogger.isOn("ssl,handshake")) {
                SSLLogger.fine(
                        "Produced CertificateVerify handshake message", cvm);
            }

            // Output the handshake message.
            cvm.write(chc.handshakeOutput);
            chc.handshakeOutput.flush();

            // The handshake message has been delivered.
            return null;
        }
    }

    /**
     * The "CertificateVerify" handshake message consumer.
     */
    private static final
            class T12CertificateVerifyConsumer implements SSLConsumer {
        // Prevent instantiation of this class.
        private T12CertificateVerifyConsumer() {
            // blank
        }

        @Override
        public void consume(ConnectionContext context,
                ByteBuffer message) throws IOException {
            // The consuming happens in server side only.
            ServerHandshakeContext shc = (ServerHandshakeContext)context;

            // Clean up this consumer
            shc.handshakeConsumers.remove(SSLHandshake.CERTIFICATE_VERIFY.id);

            // Ensure that the CV message follows the CKE
            if (shc.handshakeConsumers.containsKey(
                    SSLHandshake.CLIENT_KEY_EXCHANGE.id)) {
                throw shc.conContext.fatal(Alert.UNEXPECTED_MESSAGE,
                        "Unexpected CertificateVerify handshake message");
            }

            T12CertificateVerifyMessage cvm =
                    new T12CertificateVerifyMessage(shc, message);
            if (SSLLogger.isOn && SSLLogger.isOn("ssl,handshake")) {
                SSLLogger.fine(
                        "Consuming CertificateVerify handshake message", cvm);
            }

            //
            // update
            //
            // Need no additional validation.

            //
            // produce
            //
            // Need no new handshake message producers here.
        }
    }

    /**
     * The CertificateVerify handshake message (TLS 1.3).
     */
    static final class T13CertificateVerifyMessage extends HandshakeMessage {
        private static final byte[] serverSignHead = new byte[] {
            // repeated 0x20 for 64 times
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,

            // "TLS 1.3, server CertificateVerify" + 0x00
            (byte)0x54, (byte)0x4c, (byte)0x53, (byte)0x20,
            (byte)0x31, (byte)0x2e, (byte)0x33, (byte)0x2c,
            (byte)0x20, (byte)0x73, (byte)0x65, (byte)0x72,
            (byte)0x76, (byte)0x65, (byte)0x72, (byte)0x20,
            (byte)0x43, (byte)0x65, (byte)0x72, (byte)0x74,
            (byte)0x69, (byte)0x66, (byte)0x69, (byte)0x63,
            (byte)0x61, (byte)0x74, (byte)0x65, (byte)0x56,
            (byte)0x65, (byte)0x72, (byte)0x69, (byte)0x66,
            (byte)0x79, (byte)0x00
        };

        private static final byte[] clientSignHead = new byte[] {
            // repeated 0x20 for 64 times
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,
            (byte)0x20, (byte)0x20, (byte)0x20, (byte)0x20,

            // "TLS 1.3, client CertificateVerify" + 0x00
            (byte)0x54, (byte)0x4c, (byte)0x53, (byte)0x20,
            (byte)0x31, (byte)0x2e, (byte)0x33, (byte)0x2c,
            (byte)0x20, (byte)0x63, (byte)0x6c, (byte)0x69,
            (byte)0x65, (byte)0x6e, (byte)0x74, (byte)0x20,
            (byte)0x43, (byte)0x65, (byte)0x72, (byte)0x74,
            (byte)0x69, (byte)0x66, (byte)0x69, (byte)0x63,
            (byte)0x61, (byte)0x74, (byte)0x65, (byte)0x56,
            (byte)0x65, (byte)0x72, (byte)0x69, (byte)0x66,
            (byte)0x79, (byte)0x00
        };


        // the signature algorithm
        private final SignatureScheme signatureScheme;

        // signature bytes
        private final byte[] signature;

        T13CertificateVerifyMessage(HandshakeContext context,
                X509Possession x509Possession) throws IOException {
            super(context);

            Map.Entry<SignatureScheme, Signature> schemeAndSigner =
                    SignatureScheme.getSignerOfPreferableAlgorithm(
                    context.sslConfig,
                    context.algorithmConstraints,
                    context.peerRequestedSignatureSchemes,
                    x509Possession,
                    context.negotiatedProtocol);
            if (schemeAndSigner == null) {
                // Unlikely, the credential's generator should have
                // selected the preferable signature algorithm properly.
                throw context.conContext.fatal(Alert.INTERNAL_ERROR,
                    "No supported CertificateVerify signature algorithm for " +
                    x509Possession.popPrivateKey.getAlgorithm() +
                    "  key");
            }

            this.signatureScheme = schemeAndSigner.getKey();

            byte[] hashValue = context.handshakeHash.digest();
            byte[] contentCovered;
            if (context.sslConfig.isClientMode) {
                contentCovered = Arrays.copyOf(clientSignHead,
                        clientSignHead.length + hashValue.length);
                System.arraycopy(hashValue, 0, contentCovered,
                        clientSignHead.length, hashValue.length);
            } else {
                contentCovered = Arrays.copyOf(serverSignHead,
                        serverSignHead.length + hashValue.length);
                System.arraycopy(hashValue, 0, contentCovered,
                        serverSignHead.length, hashValue.length);
            }

            byte[] temporary;
            try {
                Signature signer = schemeAndSigner.getValue();
                signer.update(contentCovered);
                temporary = signer.sign();
            } catch (SignatureException ikse) {
                throw context.conContext.fatal(Alert.HANDSHAKE_FAILURE,
                        "Cannot produce CertificateVerify signature", ikse);
            }

            this.signature = temporary;
        }

        T13CertificateVerifyMessage(HandshakeContext context,
                ByteBuffer m) throws IOException {
             super(context);

            // struct {
            //     SignatureAndHashAlgorithm algorithm;
            //     opaque signature<0..2^16-1>;
            // } DigitallySigned;
            if (m.remaining() < 4) {
                throw context.conContext.fatal(Alert.ILLEGAL_PARAMETER,
                    "Invalid CertificateVerify message: no sufficient data");
            }

            // SignatureAndHashAlgorithm algorithm
            int ssid = Record.getInt16(m);
            this.signatureScheme = SignatureScheme.valueOf(ssid);
            if (signatureScheme == null) {
                throw context.conContext.fatal(Alert.HANDSHAKE_FAILURE,
                        "Invalid signature algorithm (" + ssid +
                        ") used in CertificateVerify handshake message");
            }

            if (!context.localSupportedSignAlgs.contains(signatureScheme)) {
                throw context.conContext.fatal(Alert.HANDSHAKE_FAILURE,
                        "Unsupported signature algorithm (" +
                        signatureScheme.name +
                        ") used in CertificateVerify handshake message");
            }

            // read and verify the signature
            X509Credentials x509Credentials = null;
            for (SSLCredentials cd : context.handshakeCredentials) {
                if (cd instanceof X509Credentials) {
                    x509Credentials = (X509Credentials)cd;
                    break;
                }
            }

            if (x509Credentials == null ||
                    x509Credentials.popPublicKey == null) {
                throw context.conContext.fatal(Alert.HANDSHAKE_FAILURE,
                    "No X509 credentials negotiated for CertificateVerify");
            }

            // opaque signature<0..2^16-1>;
            this.signature = Record.getBytes16(m);

            byte[] hashValue = context.handshakeHash.digest();
            byte[] contentCovered;
            if (context.sslConfig.isClientMode) {
                contentCovered = Arrays.copyOf(serverSignHead,
                        serverSignHead.length + hashValue.length);
                System.arraycopy(hashValue, 0, contentCovered,
                        serverSignHead.length, hashValue.length);
            } else {
                contentCovered = Arrays.copyOf(clientSignHead,
                        clientSignHead.length + hashValue.length);
                System.arraycopy(hashValue, 0, contentCovered,
                        clientSignHead.length, hashValue.length);
            }

            try {
                Signature signer =
                    signatureScheme.getVerifier(x509Credentials.popPublicKey);
                signer.update(contentCovered);
                if (!signer.verify(signature)) {
                    throw context.conContext.fatal(Alert.HANDSHAKE_FAILURE,
                        "Invalid CertificateVerify signature");
                }
            } catch (NoSuchAlgorithmException |
                    InvalidAlgorithmParameterException nsae) {
                throw context.conContext.fatal(Alert.INTERNAL_ERROR,
                        "Unsupported signature algorithm (" +
                        signatureScheme.name +
                        ") used in CertificateVerify handshake message", nsae);
            } catch (InvalidKeyException | SignatureException ikse) {
                throw context.conContext.fatal(Alert.HANDSHAKE_FAILURE,
                        "Cannot verify CertificateVerify signature", ikse);
            }
        }

        @Override
        public SSLHandshake handshakeType() {
            return SSLHandshake.CERTIFICATE_VERIFY;
        }

        @Override
        public int messageLength() {
            return 4 + signature.length;    //  2: signature algorithm
                                            // +2: length of signature
        }

        @Override
        public void send(HandshakeOutStream hos) throws IOException {
            hos.putInt16(signatureScheme.id);
            hos.putBytes16(signature);
        }

        @Override
        public String toString() {
            MessageFormat messageFormat = new MessageFormat(
                    """
                            "CertificateVerify": '{'
                              "signature algorithm": {0}
                              "signature": '{'
                            {1}
                              '}'
                            '}'""",
                    Locale.ENGLISH);

            HexDumpEncoder hexEncoder = new HexDumpEncoder();
            Object[] messageFields = {
                signatureScheme.name,
                Utilities.indent(
                        hexEncoder.encodeBuffer(signature), "    ")
            };

            return messageFormat.format(messageFields);
        }
    }

    /**
     * The "CertificateVerify" handshake message producer.
     */
    private static final
            class T13CertificateVerifyProducer implements HandshakeProducer {
        // Prevent instantiation of this class.
        private T13CertificateVerifyProducer() {
            // blank
        }

        @Override
        public byte[] produce(ConnectionContext context,
                HandshakeMessage message) throws IOException {
            // The producing happens in handshake context only.
            HandshakeContext hc = (HandshakeContext)context;

            X509Possession x509Possession = null;
            for (SSLPossession possession : hc.handshakePossessions) {
                if (possession instanceof X509Possession) {
                    x509Possession = (X509Possession)possession;
                    break;
                }
            }

            if (x509Possession == null ||
                    x509Possession.popPrivateKey == null) {
                if (SSLLogger.isOn && SSLLogger.isOn("ssl,handshake")) {
                    SSLLogger.fine(
                        "No X.509 credentials negotiated for CertificateVerify");
                }

                return null;
            }

            if (hc.sslConfig.isClientMode) {
                return onProduceCertificateVerify(
                        (ClientHandshakeContext)context, x509Possession);
            } else {
                return onProduceCertificateVerify(
                        (ServerHandshakeContext)context, x509Possession);
            }
        }

        private byte[] onProduceCertificateVerify(ServerHandshakeContext shc,
                X509Possession x509Possession) throws IOException {
            T13CertificateVerifyMessage cvm =
                    new T13CertificateVerifyMessage(shc, x509Possession);
            if (SSLLogger.isOn && SSLLogger.isOn("ssl,handshake")) {
                SSLLogger.fine(
                    "Produced server CertificateVerify handshake message", cvm);
            }

            // Output the handshake message.
            cvm.write(shc.handshakeOutput);
            shc.handshakeOutput.flush();

            // The handshake message has been delivered.
            return null;
        }

        private byte[] onProduceCertificateVerify(ClientHandshakeContext chc,
                X509Possession x509Possession) throws IOException {
            T13CertificateVerifyMessage cvm =
                    new T13CertificateVerifyMessage(chc, x509Possession);
            if (SSLLogger.isOn && SSLLogger.isOn("ssl,handshake")) {
                SSLLogger.fine(
                    "Produced client CertificateVerify handshake message", cvm);
            }

            // Output the handshake message.
            cvm.write(chc.handshakeOutput);
            chc.handshakeOutput.flush();

            // The handshake message has been delivered.
            return null;
        }
    }

    /**
     * The "CertificateVerify" handshake message consumer.
     */
    private static final
            class T13CertificateVerifyConsumer implements SSLConsumer {
        // Prevent instantiation of this class.
        private T13CertificateVerifyConsumer() {
            // blank
        }

        @Override
        public void consume(ConnectionContext context,
                ByteBuffer message) throws IOException {
            // The producing happens in handshake context only.
            HandshakeContext hc = (HandshakeContext)context;

            // Clean up this consumer
            hc.handshakeConsumers.remove(SSLHandshake.CERTIFICATE_VERIFY.id);

            // Ensure that the Certificate Verify message has not been sent w/o
            // a Certificate message preceding
            if (hc.handshakeConsumers.containsKey(
                    SSLHandshake.CERTIFICATE.id)) {
                throw hc.conContext.fatal(Alert.UNEXPECTED_MESSAGE,
                                  "Unexpected Certificate Verify handshake message");
            }

            T13CertificateVerifyMessage cvm =
                    new T13CertificateVerifyMessage(hc, message);
            if (SSLLogger.isOn && SSLLogger.isOn("ssl,handshake")) {
                SSLLogger.fine(
                        "Consuming CertificateVerify handshake message", cvm);
            }

            //
            // update
            //
            // Need no additional validation.

            //
            // produce
            //
            // Need no new handshake message producers here.
        }
    }
}