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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.crypto.impl.jcajce;

import java.io.IOException;
import java.math.BigInteger;
import java.security.GeneralSecurityException;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.util.Arrays;

import javax.crypto.interfaces.DHPrivateKey;
import javax.crypto.interfaces.DHPublicKey;
import javax.crypto.spec.DHParameterSpec;
import javax.crypto.spec.DHPublicKeySpec;

import org.bouncycastle.tls.AlertDescription;
import org.bouncycastle.tls.TlsDHUtils;
import org.bouncycastle.tls.TlsFatalAlert;
import org.bouncycastle.tls.crypto.DHGroup;
import org.bouncycastle.tls.crypto.TlsAgreement;
import org.bouncycastle.tls.crypto.TlsCryptoException;
import org.bouncycastle.tls.crypto.TlsDHConfig;
import org.bouncycastle.tls.crypto.TlsDHDomain;
import org.bouncycastle.util.BigIntegers;

/**
 * JCE support class for Diffie-Hellman key pair generation and key agreement over a specified Diffie-Hellman configuration.
 */
public class JceTlsDHDomain
    implements TlsDHDomain
{
    private static byte[] encodeValue(DHParameterSpec dh, boolean padded, BigInteger x)
    {
        return padded
            ?   BigIntegers.asUnsignedByteArray(getValueLength(dh), x)
            :   BigIntegers.asUnsignedByteArray(x);
    }

    private static int getValueLength(DHParameterSpec dh)
    {
        return (dh.getP().bitLength() + 7) / 8;
    }

    public static JceTlsSecret calculateDHAgreement(JcaTlsCrypto crypto, DHPrivateKey privateKey, DHPublicKey publicKey,
        boolean padded) throws IOException
    {
        try
        {
            /*
             * RFC 5246 8.1.2. Leading bytes of Z that contain all zero bits are stripped before it
             * is used as the pre_master_secret. We use the convention established by the JSSE to
             * signal this by asking for "TlsPremasterSecret".
             */
            byte[] secret = crypto.calculateKeyAgreement("DH", privateKey, publicKey, "TlsPremasterSecret");

            if (padded)
            {
                int length = getValueLength(privateKey.getParams());
                byte[] tmp = new byte[length];
                System.arraycopy(secret, 0, tmp, length - secret.length, secret.length);
                Arrays.fill(secret, (byte)0);
                secret = tmp;
            }

            return crypto.adoptLocalSecret(secret);
        }
        catch (GeneralSecurityException e)
        {
            throw new TlsCryptoException("cannot calculate secret", e);
        }
    }

    public static DHParameterSpec getParameters(TlsDHConfig dhConfig)
    {
        DHGroup dhGroup = TlsDHUtils.getDHGroup(dhConfig);
        if (dhGroup == null)
        {
            throw new IllegalArgumentException("No DH configuration provided");
        }

        // NOTE: dhGroup.getQ() is ignored here
        return new DHParameterSpec(dhGroup.getP(), dhGroup.getG(), dhGroup.getL());
    }

    protected final JcaTlsCrypto crypto;
    protected final TlsDHConfig dhConfig;
    protected final DHParameterSpec dhParameterSpec;

    public JceTlsDHDomain(JcaTlsCrypto crypto, TlsDHConfig dhConfig)
    {
        this.crypto = crypto;
        this.dhConfig = dhConfig;
        this.dhParameterSpec = getParameters(dhConfig);
    }

    public JceTlsSecret calculateDHAgreement(DHPrivateKey privateKey, DHPublicKey publicKey)
        throws IOException
    {
        return calculateDHAgreement(crypto, privateKey, publicKey, dhConfig.isPadded());
    }

    public TlsAgreement createDH()
    {
        return new JceTlsDH(this);
    }

    public BigInteger decodeParameter(byte[] encoding) throws IOException
    {
        if (dhConfig.isPadded() && getValueLength(dhParameterSpec) != encoding.length)
        {
            throw new TlsFatalAlert(AlertDescription.illegal_parameter);
        }

        return new BigInteger(1, encoding);
    }

    public DHPublicKey decodePublicKey(byte[] encoding) throws IOException
    {
        /*
         * RFC 7919 3. [..] the client MUST verify that dh_Ys is in the range 1 < dh_Ys < dh_p - 1.
         * If dh_Ys is not in this range, the client MUST terminate the connection with a fatal
         * handshake_failure(40) alert.
         */
        try
        {
            BigInteger y = decodeParameter(encoding);

            KeyFactory keyFactory = crypto.getHelper().createKeyFactory("DH");

            return (DHPublicKey)keyFactory.generatePublic(new DHPublicKeySpec(y, dhParameterSpec.getP(), dhParameterSpec.getG()));
        }
        catch (IOException e)
        {
            throw e;
        }
        catch (Exception e)
        {
            throw new TlsFatalAlert(AlertDescription.handshake_failure, e);
        }
    }

    public byte[] encodeParameter(BigInteger x) throws IOException
    {
        return encodeValue(dhParameterSpec, dhConfig.isPadded(), x);
    }

    public byte[] encodePublicKey(DHPublicKey publicKey) throws IOException
    {
        return encodeValue(dhParameterSpec, true, publicKey.getY());
    }

    public KeyPair generateKeyPair() throws IOException
    {
        try
        {
            KeyPairGenerator keyPairGenerator = crypto.getHelper().createKeyPairGenerator("DH");
            keyPairGenerator.initialize(dhParameterSpec, crypto.getSecureRandom());
            return keyPairGenerator.generateKeyPair();
        }
        catch (GeneralSecurityException e)
        {
            throw new TlsCryptoException("unable to create key pair", e);
        }
    }
}