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The Bouncy Castle Java APIs for CMS, PKCS, EAC, TSP, CMP, CRMF, OCSP, and certificate generation. 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.

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package org.bouncycastle.operator;

import java.io.IOException;
import java.io.OutputStream;

import org.bouncycastle.util.Arrays;

/**
 * A generic class for capturing the mac data at the end of a encrypted data stream.
 * 
 * Note: this class will not close the underlying stream.
 * 
 */
public class MacCaptureStream
    extends OutputStream
{
    private final OutputStream cOut;
    private final byte[] mac;

    int macIndex = 0;

    public MacCaptureStream(OutputStream cOut, int macLength)
    {
        this.cOut = cOut;
        this.mac = new byte[macLength];
    }

    public void write(byte[] buf, int off, int len)
        throws IOException
    {
        if (len >= mac.length)
        {
            cOut.write(mac, 0, macIndex);
            macIndex = mac.length;
            System.arraycopy(buf, off + len - mac.length, mac, 0, mac.length);
            cOut.write(buf, off, len - mac.length);
        }
        else
        {
            for (int i = 0; i != len; i++)
            {
                write(buf[off + i]);
            }
        }
    }

    public void write(int b)
        throws IOException
    {
        if (macIndex == mac.length)
        {
             byte b1 = mac[0];
             System.arraycopy(mac, 1, mac, 0, mac.length - 1);
             mac[mac.length - 1] = (byte)b;
             cOut.write(b1);
        }
        else
        {
            mac[macIndex++] = (byte)b;
        }
    }

    public byte[] getMac()
    {
        return Arrays.clone(mac);
    }
}