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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;

public class KeyShareEntry
{
    private static boolean checkKeyExchangeLength(int length)
    {
        return 0 < length && length < (1 << 16);
    }

    protected final int namedGroup;
    protected final byte[] keyExchange;

    /**
     * @param namedGroup
     *            {@link NamedGroup}
     * @param keyExchange
     */
    public KeyShareEntry(int namedGroup, byte[] keyExchange)
    {
        if (!TlsUtils.isValidUint16(namedGroup))
        {
            throw new IllegalArgumentException("'namedGroup' should be a uint16");
        }
        if (null == keyExchange)
        {
            throw new NullPointerException("'keyExchange' cannot be null");
        }
        if (!checkKeyExchangeLength(keyExchange.length))
        {
            throw new IllegalArgumentException("'keyExchange' must have length from 1 to (2^16 - 1)");
        }

        this.namedGroup = namedGroup;
        this.keyExchange = keyExchange;
    }

    /**
     * @return {@link NamedGroup}
     */
    public int getNamedGroup()
    {
        return namedGroup;
    }

    public byte[] getKeyExchange()
    {
        return keyExchange;
    }

    /**
     * Encode this {@link KeyShareEntry} to an {@link OutputStream}.
     *
     * @param output the {@link OutputStream} to encode to.
     * @throws IOException
     */
    public void encode(OutputStream output)
        throws IOException
    {
        TlsUtils.writeUint16(getNamedGroup(), output);
        TlsUtils.writeOpaque16(getKeyExchange(), output);
    }

    /**
     * Parse a {@link KeyShareEntry} from an {@link InputStream}.
     *
     * @param input the {@link InputStream} to parse from.
     * @return a {@link KeyShareEntry} object.
     * @throws IOException
     */
    public static KeyShareEntry parse(InputStream input)
        throws IOException
    {
        int namedGroup = TlsUtils.readUint16(input);
        byte[] keyExchange = TlsUtils.readOpaque16(input, 1);
        return new KeyShareEntry(namedGroup, keyExchange);
    }
}