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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.security.KeyFactory;
import java.security.PublicKey;
import java.security.spec.EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;

import org.bouncycastle.asn1.ASN1Encoding;
import org.bouncycastle.asn1.ASN1ObjectIdentifier;
import org.bouncycastle.asn1.x509.AlgorithmIdentifier;
import org.bouncycastle.asn1.x509.SubjectPublicKeyInfo;
import org.bouncycastle.tls.AlertDescription;
import org.bouncycastle.tls.TlsFatalAlert;

class XDHUtil
{
    static PublicKey decodePublicKey(JcaTlsCrypto crypto, String keyFactoryAlgorithm,
        ASN1ObjectIdentifier algorithmOID, byte[] encoding) throws TlsFatalAlert
    {
        try
        {
            KeyFactory kf = crypto.getHelper().createKeyFactory(keyFactoryAlgorithm);

            // More efficient BC-specific method
//            if (kf.getProvider() instanceof BouncyCastleProvider)
//            {
//                try
//                {
//                    EncodedKeySpec keySpec = new RawEncodedKeySpec(encoding);
//                    return kf.generatePublic(keySpec);
//                }
//                catch (Exception e)
//                {
//                    // Fallback to X.509
//                }
//            }

            EncodedKeySpec keySpec = createX509EncodedKeySpec(algorithmOID, encoding);
            return kf.generatePublic(keySpec);
        }
        catch (Exception e)
        {
            throw new TlsFatalAlert(AlertDescription.illegal_parameter, e);
        }
    }

    static byte[] encodePublicKey(PublicKey publicKey) throws TlsFatalAlert
    {
        // More efficient BC-specific method
//        if (publicKey instanceof XDHPublicKey)
//        {
//            return ((XDHPublicKey)publicKey).getUEncoding();
//        }

        if (!"X.509".equals(publicKey.getFormat()))
        {
            throw new TlsFatalAlert(AlertDescription.internal_error, "Public key format unrecognized");
        }

        try
        {
            SubjectPublicKeyInfo spki = SubjectPublicKeyInfo.getInstance(publicKey.getEncoded());
            return spki.getPublicKeyData().getOctets();
        }
        catch (Exception e)
        {
            throw new TlsFatalAlert(AlertDescription.internal_error, e);
        }
    }

    private static X509EncodedKeySpec createX509EncodedKeySpec(ASN1ObjectIdentifier oid, byte[] encoding)
        throws IOException
    {
        AlgorithmIdentifier algID = new AlgorithmIdentifier(oid);
        SubjectPublicKeyInfo spki = new SubjectPublicKeyInfo(algID, encoding);
        return new X509EncodedKeySpec(spki.getEncoded(ASN1Encoding.DER));
    }
}