Android Open Source - RadaeePDF-B4A P D F A E S Stream

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License

The source code is released under:
Apache License
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Java Source Code

package com.radaee.util;
/*from www .  j a va 2 s  .com*/
import java.io.RandomAccessFile;

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

import android.util.Log;

import com.radaee.pdf.Document.PDFStream;

/**
 * a class to decrypt PDF file that encrypted by PDFAESEnc class<br/>
 * this is read-only for encrypted PDF file.
 * @author radaee
 */
public class PDFAESStream implements PDFStream
{
  private class BlockEntry
  {
    int off;
    int len;
  }
  private RandomAccessFile m_impl = null;
  private BlockEntry[] m_entries = null;
  private Cipher m_cipher = null;
  private int m_total = 0;
  private int m_pos = 0;
  private int m_block_pos = 0;
  private byte[] m_block = null;
  /**
   * open file, that encrypted by PDFAESEnc class
   * @param filepath absolute file path
   * @param key must be 16 bytes, 24 bytes, or 32 bytes.
   * @return true or false.
   */
  public boolean open(String filepath, byte[] key)
  {
    try
    {
      m_impl = new RandomAccessFile( filepath, "r" );
      //check header first
      byte[] header = new byte[8];
      m_impl.read(header);
      if( header[0] != 'R' || header[1] != 'D' || header[2] != 'A' || header[3] != 'E' || header[4] != 'S' )
      {
        m_impl.close();
        return false;
      }
      
      //load all sections.
      int secs_cnt = m_impl.readInt();
      m_total = m_impl.readInt();
      m_entries = new BlockEntry[secs_cnt];
      int cur = 0;
      while( cur < secs_cnt )
      {
        m_entries[cur] = new BlockEntry();
        m_entries[cur].off = m_impl.readInt();
        m_entries[cur].len = m_impl.readInt();
        cur++;
      }

      //init key and Cipher object
      SecretKeySpec skey = new SecretKeySpec(key, "AES");  
      m_cipher = Cipher.getInstance("AES/CBC/PKCS7Padding");
      byte[] ivbytes = new byte[]{0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15};
      IvParameterSpec iv = new IvParameterSpec(ivbytes);//need IV in CBC mode
            m_cipher.init(Cipher.DECRYPT_MODE, skey, iv);
            
            //decrypt first blocks.
      m_block = dec_block(0);
      return true;
    }
    catch(Exception e)
    {
      Log.d("error", e.getMessage());
      return false;
    }
  }
  /**
   * free resources.<br/>
   * this method is needed when APP close the PDF.
   */
  public void close()
  {
    try
    {
      m_impl.close();
    }
    catch(Exception e)
    {
      Log.d("error", e.getMessage());
    }
  }
  private byte[] dec_block(int block)
  {
    if( block >= m_entries.length )
      return null;
    try
    {
      m_impl.seek(m_entries[block].off);
      byte[] src = new byte[m_entries[block].len];
      m_impl.read(src);
      return m_cipher.doFinal(src);
    }
    catch( Exception e )
    {
      Log.d("error", e.getMessage());
      return null;
    }
  }
  public boolean writeable()
  {
    return false;
  }

  public int get_size()
  {
    return m_total;
  }

  public int read(byte[] data)
  {
    if( m_block == null ) return 0;
    int dst_off = 0;
    int pos_old = m_pos;
    while( dst_off < data.length && m_pos < m_total )
    {
      int off = m_pos & 4095;
      while( off < m_block.length && dst_off < data.length )
      {
        data[dst_off] = m_block[off];
        dst_off++;
        off++;
      }
      seek(pos_old + dst_off);
    }
    return dst_off;
  }

  public int write(byte[] data)
  {
    return 0;
  }

  public void seek(int pos)
  {
    if( pos < 0 )
      pos = 0;
    if( pos > m_total )
      pos = m_total;
    int new_pos = pos;
    if( new_pos == m_pos ) return;
    int new_block_pos = new_pos/4096;
    if( new_block_pos == m_block_pos )
    {
      m_pos = new_pos;
    }
    else
    {
      m_block = dec_block(new_block_pos);
      m_pos = new_pos;
      m_block_pos = new_block_pos;
    }
  }

  public int tell()
  {
    return m_pos;
  }
}
Java Source Code List
