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The Bouncy Castle Java APIs for the TLS, including a JSSE provider. The APIs are designed primarily to be used in conjunction with the BC FIPS provider. The APIs may also be used with other providers although if being used in a FIPS context it is the responsibility of the user to ensure that any other providers used are FIPS certified and used appropriately.

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package org.bouncycastle.tls;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import org.bouncycastle.tls.crypto.TlsCertificate;
import org.bouncycastle.tls.crypto.TlsSecret;

/**
 * (D)TLS DH key exchange.
 */
public class TlsDHKeyExchange
    extends AbstractTlsKeyExchange
{
    private static int checkKeyExchange(int keyExchange)
    {
        switch (keyExchange)
        {
        case KeyExchangeAlgorithm.DH_DSS:
        case KeyExchangeAlgorithm.DH_RSA:
            return keyExchange;
        default:
            throw new IllegalArgumentException("unsupported key exchange algorithm");
        }
    }

    protected TlsCredentialedAgreement agreementCredentials;
    protected TlsCertificate dhPeerCertificate;

    public TlsDHKeyExchange(int keyExchange)
    {
        super(checkKeyExchange(keyExchange));
    }

    public void skipServerCredentials() throws IOException
    {
        throw new TlsFatalAlert(AlertDescription.internal_error);
    }

    public void processServerCredentials(TlsCredentials serverCredentials) throws IOException
    {
        this.agreementCredentials = TlsUtils.requireAgreementCredentials(serverCredentials);
    }

    public void processServerCertificate(Certificate serverCertificate) throws IOException
    {
        this.dhPeerCertificate = serverCertificate.getCertificateAt(0).useInRole(ConnectionEnd.server, keyExchange);
    }

    public short[] getClientCertificateTypes()
    {
        return new short[]{ ClientCertificateType.dss_fixed_dh, ClientCertificateType.rsa_fixed_dh };
    }

    public void skipClientCredentials() throws IOException
    {
        throw new TlsFatalAlert(AlertDescription.unexpected_message);
    }

    public void processClientCredentials(TlsCredentials clientCredentials) throws IOException
    {
        this.agreementCredentials = TlsUtils.requireAgreementCredentials(clientCredentials);
    }

    public void generateClientKeyExchange(OutputStream output) throws IOException
    {
        /*
         * RFC 2246 7.4.7.2 If the client certificate already contains a suitable Diffie-Hellman
         * key, then Yc is implicit and does not need to be sent again. In this case, the Client Key
         * Exchange message will be sent, but will be empty.
         */
    }

    public void processClientCertificate(Certificate clientCertificate) throws IOException
    {
        this.dhPeerCertificate = clientCertificate.getCertificateAt(0)
            .useInRole(ConnectionEnd.client, keyExchange);
    }

    public void processClientKeyExchange(InputStream input) throws IOException
    {
        // For dss_fixed_dh and rsa_fixed_dh, the key arrived in the client certificate
    }

    public boolean requiresCertificateVerify()
    {
        return false;
    }

    public TlsSecret generatePreMasterSecret() throws IOException
    {
        return agreementCredentials.generateAgreement(dhPeerCertificate);
    }
}