/*

 * Copyright (c) 2018, 2019, 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

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 */

package sun.security.ssl;

import java.io.IOException;

import java.math.BigInteger;

import java.security.GeneralSecurityException;

import java.security.InvalidKeyException;

import java.security.KeyFactory;

import java.security.KeyPair;

import java.security.KeyPairGenerator;

import java.security.NoSuchAlgorithmException;

import java.security.PrivateKey;

import java.security.PublicKey;

import java.security.SecureRandom;

import java.security.spec.InvalidKeySpecException;

import javax.crypto.interfaces.DHPublicKey;

import javax.crypto.spec.DHParameterSpec;

import javax.crypto.spec.DHPublicKeySpec;

import sun.security.action.GetPropertyAction;

import sun.security.ssl.NamedGroup.NamedGroupSpec;

import sun.security.ssl.SupportedGroupsExtension.SupportedGroups;

import sun.security.ssl.X509Authentication.X509Possession;

import sun.security.util.KeyUtil;

final class DHKeyExchange {

    static final SSLPossessionGenerator poGenerator =

            new DHEPossessionGenerator(false);

    static final SSLPossessionGenerator poExportableGenerator =

            new DHEPossessionGenerator(true);

    static final SSLKeyAgreementGenerator kaGenerator =

            new DHEKAGenerator();

    static final class DHECredentials implements NamedGroupCredentials {

        final DHPublicKey popPublicKey;

        final NamedGroup namedGroup;

        DHECredentials(DHPublicKey popPublicKey, NamedGroup namedGroup) {

            this.popPublicKey = popPublicKey;

            this.namedGroup = namedGroup;

        }

        @Override

        public PublicKey getPublicKey() {

            return popPublicKey;

        }

        @Override

        public NamedGroup getNamedGroup() {

            return namedGroup;

        }

        static DHECredentials valueOf(NamedGroup ng,

            byte[] encodedPublic) throws IOException, GeneralSecurityException {

            if (ng.spec != NamedGroupSpec.NAMED_GROUP_FFDHE) {

                throw new RuntimeException(

                        "Credentials decoding:  Not FFDHE named group");

            }

            if (encodedPublic == null || encodedPublic.length == 0) {

                return null;

            }

            DHParameterSpec params = (DHParameterSpec)ng.keAlgParamSpec;

            KeyFactory kf = KeyFactory.getInstance("DiffieHellman");

            DHPublicKeySpec spec = new DHPublicKeySpec(

                    new BigInteger(1, encodedPublic),

                    params.getP(), params.getG());

            DHPublicKey publicKey =

                    (DHPublicKey)kf.generatePublic(spec);

            return new DHECredentials(publicKey, ng);

        }

    }

    static final class DHEPossession implements NamedGroupPossession {

        final PrivateKey privateKey;

        final DHPublicKey publicKey;

        final NamedGroup namedGroup;

        DHEPossession(NamedGroup namedGroup, SecureRandom random) {

            try {

                KeyPairGenerator kpg =

                        KeyPairGenerator.getInstance("DiffieHellman");

                kpg.initialize(namedGroup.keAlgParamSpec, random);

                KeyPair kp = generateDHKeyPair(kpg);

                if (kp == null) {

                    throw new RuntimeException("Could not generate DH keypair");

                }

                privateKey = kp.getPrivate();

                publicKey = (DHPublicKey)kp.getPublic();

            } catch (GeneralSecurityException gse) {

                throw new RuntimeException(

                        "Could not generate DH keypair", gse);

            }

            this.namedGroup = namedGroup;

        }

        DHEPossession(int keyLength, SecureRandom random) {

            DHParameterSpec params =

                    PredefinedDHParameterSpecs.definedParams.get(keyLength);

            try {

                KeyPairGenerator kpg =

                    KeyPairGenerator.getInstance("DiffieHellman");

                if (params != null) {

                    kpg.initialize(params, random);

                } else {

                    kpg.initialize(keyLength, random);

                }

                KeyPair kp = generateDHKeyPair(kpg);

                if (kp == null) {

                    throw new RuntimeException(

                            "Could not generate DH keypair of " +

                            keyLength + " bits");

                }

                privateKey = kp.getPrivate();

                publicKey = (DHPublicKey)kp.getPublic();

            } catch (GeneralSecurityException gse) {

                throw new RuntimeException(

                        "Could not generate DH keypair", gse);

            }

            this.namedGroup = NamedGroup.valueOf(publicKey.getParams());

        }

        DHEPossession(DHECredentials credentials, SecureRandom random) {

            try {

                KeyPairGenerator kpg =

                        KeyPairGenerator.getInstance("DiffieHellman");

                kpg.initialize(credentials.popPublicKey.getParams(), random);

                KeyPair kp = generateDHKeyPair(kpg);

                if (kp == null) {

                    throw new RuntimeException("Could not generate DH keypair");

                }

                privateKey = kp.getPrivate();

                publicKey = (DHPublicKey)kp.getPublic();

            } catch (GeneralSecurityException gse) {

                throw new RuntimeException(

                        "Could not generate DH keypair", gse);

            }

            this.namedGroup = credentials.namedGroup;

        }

        // Generate and validate DHPublicKeySpec

        private KeyPair generateDHKeyPair(

                KeyPairGenerator kpg) throws GeneralSecurityException {

            boolean doExtraValidation =

                    (!KeyUtil.isOracleJCEProvider(kpg.getProvider().getName()));

            boolean isRecovering = false;

            for (int i = 0; i <= 2; i++) {      // Try to recover from failure.

                KeyPair kp = kpg.generateKeyPair();

                // validate the Diffie-Hellman public key

                if (doExtraValidation) {

                    DHPublicKeySpec spec = getDHPublicKeySpec(kp.getPublic());

                    try {

                        KeyUtil.validate(spec);

                    } catch (InvalidKeyException ivke) {

                        if (isRecovering) {

                            throw ivke;

                        }

                        // otherwise, ignore the exception and try again

                        isRecovering = true;

                        continue;

                    }

                }

                return kp;

            }

            return null;

        }

        private static DHPublicKeySpec getDHPublicKeySpec(PublicKey key) {

            if (key instanceof DHPublicKey) {

                DHPublicKey dhKey = (DHPublicKey)key;

                DHParameterSpec params = dhKey.getParams();

                return new DHPublicKeySpec(dhKey.getY(),

                                        params.getP(), params.getG());

            }

            try {

                KeyFactory factory = KeyFactory.getInstance("DiffieHellman");

                return factory.getKeySpec(key, DHPublicKeySpec.class);

            } catch (NoSuchAlgorithmException | InvalidKeySpecException e) {

                // unlikely

                throw new RuntimeException("Unable to get DHPublicKeySpec", e);

            }

        }

        @Override

        public byte[] encode() {

            // Note: the DH public value is encoded as a big-endian integer

            // and padded to the left with zeros to the size of p in bytes.

            byte[] encoded = Utilities.toByteArray(publicKey.getY());

            int pSize = (KeyUtil.getKeySize(publicKey) + 7) >>> 3;

            if (pSize > 0 && encoded.length < pSize) {

                byte[] buffer = new byte[pSize];

                System.arraycopy(encoded, 0,

                        buffer, pSize - encoded.length, encoded.length);

                encoded = buffer;

            }

            return encoded;

        }

        @Override

        public PublicKey getPublicKey() {

            return publicKey;

        }

        @Override

        public NamedGroup getNamedGroup() {

            return namedGroup;

        }

        @Override

        public PrivateKey getPrivateKey() {

            return privateKey;

        }

    }

    private static final class

            DHEPossessionGenerator implements SSLPossessionGenerator {

        // Flag to use smart ephemeral DH key which size matches the

        // corresponding authentication key

        private static final boolean useSmartEphemeralDHKeys;

        // Flag to use legacy ephemeral DH key which size is 512 bits for

        // exportable cipher suites, and 768 bits for others

        private static final boolean useLegacyEphemeralDHKeys;

        // The customized ephemeral DH key size for non-exportable

        // cipher suites.

        private static final int customizedDHKeySize;

        // Is it for exportable cipher suite?

        private final boolean exportable;

        static {

            String property = GetPropertyAction.privilegedGetProperty(

                    "jdk.tls.ephemeralDHKeySize");

            if (property == null || property.isEmpty()) {

                useLegacyEphemeralDHKeys = false;

                useSmartEphemeralDHKeys = false;

                customizedDHKeySize = -1;

            } else if ("matched".equals(property)) {

                useLegacyEphemeralDHKeys = false;

                useSmartEphemeralDHKeys = true;

                customizedDHKeySize = -1;

            } else if ("legacy".equals(property)) {

                useLegacyEphemeralDHKeys = true;

                useSmartEphemeralDHKeys = false;

                customizedDHKeySize = -1;

            } else {

                useLegacyEphemeralDHKeys = false;

                useSmartEphemeralDHKeys = false;

                try {

                    // DH parameter generation can be extremely slow, best to

                    // use one of the supported pre-computed DH parameters

                    // (see DHCrypt class).

                    customizedDHKeySize = Integer.parseUnsignedInt(property);

                    if (customizedDHKeySize < 1024 ||

                            customizedDHKeySize > 8192 ||

                            (customizedDHKeySize & 0x3f) != 0) {

                        throw new IllegalArgumentException(

                            "Unsupported customized DH key size: " +

                            customizedDHKeySize + ". " +

                            "The key size must be multiple of 64, " +

                            "and range from 1024 to 8192 (inclusive)");

                    }

                } catch (NumberFormatException nfe) {

                    throw new IllegalArgumentException(

                        "Invalid system property jdk.tls.ephemeralDHKeySize");

                }

            }

        }

        // Prevent instantiation of this class.

        private DHEPossessionGenerator(boolean exportable) {

            this.exportable = exportable;

        }

        // Used for ServerKeyExchange, TLS 1.2 and prior versions.

        @Override

        public SSLPossession createPossession(HandshakeContext context) {

            NamedGroup preferableNamedGroup;

            if (!useLegacyEphemeralDHKeys &&

                    (context.clientRequestedNamedGroups != null) &&

                    (!context.clientRequestedNamedGroups.isEmpty())) {

                preferableNamedGroup =

                        SupportedGroups.getPreferredGroup(context.negotiatedProtocol,

                                context.algorithmConstraints,

                                new NamedGroupSpec [] {

                                    NamedGroupSpec.NAMED_GROUP_FFDHE },

                                context.clientRequestedNamedGroups);

                if (preferableNamedGroup != null) {

                    return new DHEPossession(preferableNamedGroup,

                                context.sslContext.getSecureRandom());

                }

            }

            /*

             * 768 bits ephemeral DH private keys were used to be used in

             * ServerKeyExchange except that exportable ciphers max out at 512

             * bits modulus values. We still adhere to this behavior in legacy

             * mode (system property "jdk.tls.ephemeralDHKeySize" is defined

             * as "legacy").

             *

             * Old JDK (JDK 7 and previous) releases don't support DH keys

             * bigger than 1024 bits. We have to consider the compatibility

             * requirement. 1024 bits DH key is always used for non-exportable

             * cipher suites in default mode (system property

             * "jdk.tls.ephemeralDHKeySize" is not defined).

             *

             * However, if applications want more stronger strength, setting

             * system property "jdk.tls.ephemeralDHKeySize" to "matched"

             * is a workaround to use ephemeral DH key which size matches the

             * corresponding authentication key. For example, if the public key

             * size of an authentication certificate is 2048 bits, then the

             * ephemeral DH key size should be 2048 bits accordingly unless

             * the cipher suite is exportable.  This key sizing scheme keeps

             * the cryptographic strength consistent between authentication

             * keys and key-exchange keys.

             *

             * Applications may also want to customize the ephemeral DH key

             * size to a fixed length for non-exportable cipher suites. This

             * can be approached by setting system property

             * "jdk.tls.ephemeralDHKeySize" to a valid positive integer between

             * 1024 and 8192 bits, inclusive.

             *

             * Note that the minimum acceptable key size is 1024 bits except

             * exportable cipher suites or legacy mode.

             *

             * Note that per RFC 2246, the key size limit of DH is 512 bits for

             * exportable cipher suites.  Because of the weakness, exportable

             * cipher suites are deprecated since TLS v1.1 and they are not

             * enabled by default in Oracle provider. The legacy behavior is

             * reserved and 512 bits DH key is always used for exportable

             * cipher suites.

             */

            int keySize = exportable ? 512 : 1024;           // default mode

            if (!exportable) {

                if (useLegacyEphemeralDHKeys) {          // legacy mode

                    keySize = 768;

                } else if (useSmartEphemeralDHKeys) {    // matched mode

                    PrivateKey key = null;

                    ServerHandshakeContext shc =

                            (ServerHandshakeContext)context;

                    if (shc.interimAuthn instanceof X509Possession) {

                        key = ((X509Possession)shc.interimAuthn).popPrivateKey;

                    }

                    if (key != null) {

                        int ks = KeyUtil.getKeySize(key);

                        // DH parameter generation can be extremely slow, make

                        // sure to use one of the supported pre-computed DH

                        // parameters.

                        //

                        // Old deployed applications may not be ready to

                        // support DH key sizes bigger than 2048 bits.  Please

                        // DON'T use value other than 1024 and 2048 at present.

                        // May improve the underlying providers and key size

                        // limit in the future when the compatibility and

                        // interoperability impact is limited.

                        keySize = ks <= 1024 ? 1024 : 2048;

                    } // Otherwise, anonymous cipher suites, 1024-bit is used.

                } else if (customizedDHKeySize > 0) {    // customized mode

                    keySize = customizedDHKeySize;

                }

            }

            return new DHEPossession(

                    keySize, context.sslContext.getSecureRandom());

        }

    }

    private static final

            class DHEKAGenerator implements SSLKeyAgreementGenerator {

        private static final DHEKAGenerator instance = new DHEKAGenerator();

        // Prevent instantiation of this class.

        private DHEKAGenerator() {

            // blank

        }

        @Override

        public SSLKeyDerivation createKeyDerivation(

                HandshakeContext context) throws IOException {

            DHEPossession dhePossession = null;

            DHECredentials dheCredentials = null;

            for (SSLPossession poss : context.handshakePossessions) {

                if (!(poss instanceof DHEPossession)) {

                    continue;

                }

                DHEPossession dhep = (DHEPossession)poss;

                for (SSLCredentials cred : context.handshakeCredentials) {

                    if (!(cred instanceof DHECredentials)) {

                        continue;

                    }

                    DHECredentials dhec = (DHECredentials)cred;

                    if (dhep.namedGroup != null && dhec.namedGroup != null) {

                        if (dhep.namedGroup.equals(dhec.namedGroup)) {

                            dheCredentials = (DHECredentials)cred;

                            break;

                        }

                    } else {

                        DHParameterSpec pps = dhep.publicKey.getParams();

                        DHParameterSpec cps = dhec.popPublicKey.getParams();

                        if (pps.getP().equals(cps.getP()) &&

                                pps.getG().equals(cps.getG())) {

                            dheCredentials = (DHECredentials)cred;

                            break;

                        }

                    }

                }

                if (dheCredentials != null) {

                    dhePossession = (DHEPossession)poss;

                    break;

                }

            }

            if (dhePossession == null || dheCredentials == null) {

                throw context.conContext.fatal(Alert.HANDSHAKE_FAILURE,

                    "No sufficient DHE key agreement parameters negotiated");

            }

            return new KAKeyDerivation("DiffieHellman", context,

                    dhePossession.privateKey, dheCredentials.popPublicKey);

        }

    }

}