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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.math.BigInteger;
import java.security.AlgorithmParameters;
import java.security.spec.AlgorithmParameterSpec;
import java.security.spec.KeySpec;

import javax.crypto.spec.DHParameterSpec;

import org.bouncycastle.jcajce.spec.DHDomainParameterSpec;
import org.bouncycastle.jcajce.spec.DHExtendedPublicKeySpec;
import org.bouncycastle.tls.crypto.DHGroup;

class DHUtil
{
    static AlgorithmParameterSpec createInitSpec(DHGroup dhGroup)
    {
        // NOTE: A BC-specific spec, so other providers probably won't see Q 
        return new DHDomainParameterSpec(dhGroup.getP(), dhGroup.getQ(), dhGroup.getG(), dhGroup.getL());
    }

    static KeySpec createPublicKeySpec(BigInteger y, DHParameterSpec dhSpec)
    {
        // NOTE: A BC-specific spec, so other providers probably won't see Q 
        return new DHExtendedPublicKeySpec(y, dhSpec);
    }

    static AlgorithmParameters getAlgorithmParameters(JcaTlsCrypto crypto, DHGroup dhGroup)
    {
        return getAlgorithmParameters(crypto, createInitSpec(dhGroup));
    }

    static AlgorithmParameters getAlgorithmParameters(JcaTlsCrypto crypto, AlgorithmParameterSpec initSpec)
    {
        try
        {
            AlgorithmParameters dhAlgParams = crypto.getHelper().createAlgorithmParameters("DiffieHellman");
            dhAlgParams.init(initSpec);

            DHParameterSpec dhSpec = (DHParameterSpec)dhAlgParams.getParameterSpec(DHParameterSpec.class);
            if (null != dhSpec)
            {
                return dhAlgParams;
            }
        }
        catch (AssertionError e)
        {
        }
        catch (Exception e)
        {
        }

        return null;
    }

    static DHParameterSpec getDHParameterSpec(JcaTlsCrypto crypto, DHGroup dhGroup)
    {
        return getDHParameterSpec(crypto, createInitSpec(dhGroup));
    }

    static DHParameterSpec getDHParameterSpec(JcaTlsCrypto crypto, AlgorithmParameterSpec initSpec)
    {
        try
        {
            AlgorithmParameters dhAlgParams = crypto.getHelper().createAlgorithmParameters("DiffieHellman");
            dhAlgParams.init(initSpec);

            DHParameterSpec dhSpec = (DHParameterSpec)dhAlgParams.getParameterSpec(DHParameterSpec.class);
            if (null != dhSpec)
            {
                return dhSpec;
            }
        }
        catch (AssertionError e)
        {
        }
        catch (Exception e)
        {
        }

        return null;
    }

    static BigInteger getQ(DHParameterSpec dhSpec)
    {
        return dhSpec instanceof DHDomainParameterSpec ? ((DHDomainParameterSpec)dhSpec).getQ() : null;
    }

    static boolean isGroupSupported(JcaTlsCrypto crypto, DHGroup dhGroup)
    {
        return null != dhGroup && null != getDHParameterSpec(crypto, dhGroup);
    }
}