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The Bouncy Castle Java API for handling the OpenPGP protocol. This jar contains the OpenPGP API for JDK 1.5 to JDK 1.7. The APIs can be used in conjunction with a JCE/JCA provider such as the one provided with the Bouncy Castle Cryptography APIs.

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package org.bouncycastle.bcpg.attr;

import org.bouncycastle.bcpg.UserAttributeSubpacket;
import org.bouncycastle.bcpg.UserAttributeSubpacketTags;

import java.io.ByteArrayOutputStream;
import java.io.IOException;

/**
 * Basic type for a image attribute packet.
 */
public class ImageAttribute 
    extends UserAttributeSubpacket
{
    public static final int JPEG = 1;

    private static final byte[] ZEROES = new byte[12];

    private int     hdrLength;
    private int     version;
    private int     encoding;
    private byte[]  imageData;
    
    public ImageAttribute(
        byte[]    data)
    {
        super(UserAttributeSubpacketTags.IMAGE_ATTRIBUTE, data);
        
        hdrLength = ((data[1] & 0xff) << 8) | (data[0] & 0xff);
        version = data[2] & 0xff;
        encoding = data[3] & 0xff;
        
        imageData = new byte[data.length - hdrLength];
        System.arraycopy(data, hdrLength, imageData, 0, imageData.length);
    }

    public ImageAttribute(
        int imageType,
        byte[] imageData)
    {
        this(toByteArray(imageType, imageData));
    }

    private static byte[] toByteArray(int imageType, byte[] imageData)
    {
        ByteArrayOutputStream bOut = new ByteArrayOutputStream();

        try
        {
            bOut.write(0x10); bOut.write(0x00); bOut.write(0x01);
            bOut.write(imageType);
            bOut.write(ZEROES);
            bOut.write(imageData);
        }
        catch (IOException e)
        {
            throw new RuntimeException("unable to encode to byte array!");
        }

        return bOut.toByteArray();
    }

    public int version()
    {
        return version;
    }
    
    public int getEncoding()
    {
        return encoding;
    }
    
    public byte[] getImageData()
    {
        return imageData;
    }
}