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The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.5 to JDK 1.8. Note: this package includes the NTRU encryption algorithms.
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package org.bouncycastle.crypto.tls;

import java.io.IOException;
import java.io.InputStream;
import java.util.Vector;

import org.bouncycastle.crypto.Digest;
import org.bouncycastle.crypto.Signer;
import org.bouncycastle.crypto.params.ECDomainParameters;
import org.bouncycastle.util.io.TeeInputStream;

/**
 * (D)TLS ECDHE key exchange (see RFC 4492).
 */
public class TlsECDHEKeyExchange
    extends TlsECDHKeyExchange
{
    protected TlsSignerCredentials serverCredentials = null;

    public TlsECDHEKeyExchange(int keyExchange, Vector supportedSignatureAlgorithms, int[] namedCurves,
        short[] clientECPointFormats, short[] serverECPointFormats)
    {
        super(keyExchange, supportedSignatureAlgorithms, namedCurves, clientECPointFormats, serverECPointFormats);
    }

    public void processServerCredentials(TlsCredentials serverCredentials)
        throws IOException
    {
        if (!(serverCredentials instanceof TlsSignerCredentials))
        {
            throw new TlsFatalAlert(AlertDescription.internal_error);
        }

        processServerCertificate(serverCredentials.getCertificate());

        this.serverCredentials = (TlsSignerCredentials)serverCredentials;
    }

    public byte[] generateServerKeyExchange()
        throws IOException
    {
        DigestInputBuffer buf = new DigestInputBuffer();

        this.ecAgreePrivateKey = TlsECCUtils.generateEphemeralServerKeyExchange(context.getSecureRandom(), namedCurves,
            clientECPointFormats, buf);

        /*
         * RFC 5246 4.7. digitally-signed element needs SignatureAndHashAlgorithm from TLS 1.2
         */
        SignatureAndHashAlgorithm signatureAndHashAlgorithm = TlsUtils.getSignatureAndHashAlgorithm(
            context, serverCredentials);

        Digest d = TlsUtils.createHash(signatureAndHashAlgorithm);

        SecurityParameters securityParameters = context.getSecurityParameters();
        d.update(securityParameters.clientRandom, 0, securityParameters.clientRandom.length);
        d.update(securityParameters.serverRandom, 0, securityParameters.serverRandom.length);
        buf.updateDigest(d);

        byte[] hash = new byte[d.getDigestSize()];
        d.doFinal(hash, 0);

        byte[] signature = serverCredentials.generateCertificateSignature(hash);

        DigitallySigned signed_params = new DigitallySigned(signatureAndHashAlgorithm, signature);
        signed_params.encode(buf);

        return buf.toByteArray();
    }

    public void processServerKeyExchange(InputStream input)
        throws IOException
    {
        SecurityParameters securityParameters = context.getSecurityParameters();

        SignerInputBuffer buf = new SignerInputBuffer();
        InputStream teeIn = new TeeInputStream(input, buf);

        ECDomainParameters curve_params = TlsECCUtils.readECParameters(namedCurves, clientECPointFormats, teeIn);

        byte[] point = TlsUtils.readOpaque8(teeIn);

        DigitallySigned signed_params = parseSignature(input);

        Signer signer = initVerifyer(tlsSigner, signed_params.getAlgorithm(), securityParameters);
        buf.updateSigner(signer);
        if (!signer.verifySignature(signed_params.getSignature()))
        {
            throw new TlsFatalAlert(AlertDescription.decrypt_error);
        }

        this.ecAgreePublicKey = TlsECCUtils.validateECPublicKey(TlsECCUtils.deserializeECPublicKey(
            clientECPointFormats, curve_params, point));
    }

    public void validateCertificateRequest(CertificateRequest certificateRequest)
        throws IOException
    {
        /*
         * RFC 4492 3. [...] The ECDSA_fixed_ECDH and RSA_fixed_ECDH mechanisms are usable with
         * ECDH_ECDSA and ECDH_RSA. Their use with ECDHE_ECDSA and ECDHE_RSA is prohibited because
         * the use of a long-term ECDH client key would jeopardize the forward secrecy property of
         * these algorithms.
         */
        short[] types = certificateRequest.getCertificateTypes();
        for (int i = 0; i < types.length; ++i)
        {
            switch (types[i])
            {
            case ClientCertificateType.rsa_sign:
            case ClientCertificateType.dss_sign:
            case ClientCertificateType.ecdsa_sign:
                break;
            default:
                throw new TlsFatalAlert(AlertDescription.illegal_parameter);
            }
        }
    }

    public void processClientCredentials(TlsCredentials clientCredentials)
        throws IOException
    {
        if (clientCredentials instanceof TlsSignerCredentials)
        {
            // OK
        }
        else
        {
            throw new TlsFatalAlert(AlertDescription.internal_error);
        }
    }

    protected Signer initVerifyer(TlsSigner tlsSigner, SignatureAndHashAlgorithm algorithm, SecurityParameters securityParameters)
    {
        Signer signer = tlsSigner.createVerifyer(algorithm, this.serverPublicKey);
        signer.update(securityParameters.clientRandom, 0, securityParameters.clientRandom.length);
        signer.update(securityParameters.serverRandom, 0, securityParameters.serverRandom.length);
        return signer;
    }
}