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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;

import java.io.IOException;

import org.bouncycastle.tls.AlertDescription;
import org.bouncycastle.tls.TlsFatalAlert;
import org.bouncycastle.tls.crypto.TlsCipher;
import org.bouncycastle.tls.crypto.TlsCryptoParameters;
import org.bouncycastle.tls.crypto.TlsHMAC;
import org.bouncycastle.util.Arrays;

/**
 * The NULL cipher.
 */
public class TlsNullCipher
    implements TlsCipher
{
    protected final TlsCryptoParameters cryptoParameters;
    protected final TlsSuiteHMac readMac, writeMac;

    public TlsNullCipher(TlsCryptoParameters cryptoParameters, TlsHMAC clientMac, TlsHMAC serverMac)
        throws IOException
    {
        this.cryptoParameters = cryptoParameters;

        int key_block_size = clientMac.getMacLength() + serverMac.getMacLength();
        byte[] key_block = TlsImplUtils.calculateKeyBlock(cryptoParameters, key_block_size);

        int offset = 0;

        clientMac.setKey(key_block, offset, clientMac.getMacLength());
        offset += clientMac.getMacLength();
        serverMac.setKey(key_block, offset, serverMac.getMacLength());
        offset += serverMac.getMacLength();

        if (offset != key_block_size)
        {
            throw new TlsFatalAlert(AlertDescription.internal_error);
        }

        if (cryptoParameters.isServer())
        {
            writeMac = new TlsSuiteHMac(cryptoParameters, serverMac);
            readMac = new TlsSuiteHMac(cryptoParameters, clientMac);
        }
        else
        {
            writeMac = new TlsSuiteHMac(cryptoParameters, clientMac);
            readMac = new TlsSuiteHMac(cryptoParameters, serverMac);
        }
    }

    public int getCiphertextLimit(int plaintextLimit)
    {
        return plaintextLimit + writeMac.getSize();
    }

    public int getPlaintextLimit(int ciphertextLimit)
    {
        return ciphertextLimit - writeMac.getSize();
    }

    public byte[] encodePlaintext(long seqNo, short type, byte[] plaintext, int offset, int len)
        throws IOException
    {
        byte[] mac = writeMac.calculateMac(seqNo, type, plaintext, offset, len);
        byte[] ciphertext = new byte[len + mac.length];
        System.arraycopy(plaintext, offset, ciphertext, 0, len);
        System.arraycopy(mac, 0, ciphertext, len, mac.length);
        return ciphertext;
    }

    public byte[] decodeCiphertext(long seqNo, short type, byte[] ciphertext, int offset, int len)
        throws IOException
    {
        int macSize = readMac.getSize();
        if (len < macSize)
        {
            throw new TlsFatalAlert(AlertDescription.decode_error);
        }

        int macInputLen = len - macSize;

        byte[] receivedMac = Arrays.copyOfRange(ciphertext, offset + macInputLen, offset + len);
        byte[] computedMac = readMac.calculateMac(seqNo, type, ciphertext, offset, macInputLen);

        if (!Arrays.constantTimeAreEqual(receivedMac, computedMac))
        {
            throw new TlsFatalAlert(AlertDescription.bad_record_mac);
        }

        return Arrays.copyOfRange(ciphertext, offset, offset + macInputLen);
    }
}