pdfencryption.java

非常有用的操作pdf文件的java源码

            //STEP 2
            matches = arraysEqual( u, computedValue, 16 );
        }
        return matches;
    }

    /**
     * This will compare two byte[] for equality for count number of bytes.
     *
     * @param first The first byte array.
     * @param second The second byte array.
     * @param count The number of bytes to compare.
     *
     * @return true If the arrays contain the exact same data.
     */
    private final boolean arraysEqual( byte[] first, byte[] second, int count )
    {
        boolean equal = first.length >= count && second.length >= count;
        for( int i=0; i<count && equal; i++ )
        {
            equal = first[i] == second[i];
        }
        return equal;
    }

    /**
     * This will compare two byte[] for equality.
     *
     * @param first The first byte array.
     * @param second The second byte array.
     *
     * @return true If the arrays contain the exact same data.
     */
    private final boolean arraysEqual( byte[] first, byte[] second )
    {
        boolean equal = first.length == second.length;
        for( int i=0; i<first.length && equal; i++ )
        {
            equal = first[i] == second[i];
        }
        return equal;
    }

    /**
     * This will compute the user password hash.
     *
     * @param password The plain text password.
     * @param o The owner password hash.
     * @param permissions The document permissions.
     * @param id The document id.
     * @param revision The revision of the encryption.
     * @param length The length of the encryption key.
     *
     * @return The user password.
     *
     * @throws CryptographyException If there is an error computing the user password.
     * @throws IOException If there is an IO error.
     */
    public final byte[] computeUserPassword(
        byte[] password,
        byte[] o,
        int permissions,
        byte[] id,
        int revision,
        int length )
        throws CryptographyException, IOException
    {
        ByteArrayOutputStream result = new ByteArrayOutputStream();
        //STEP 1
        byte[] encryptionKey = computeEncryptedKey( password, o, permissions, id, revision, length );

        if( revision == 2 )
        {
            //STEP 2
            rc4.setKey( encryptionKey );
            rc4.write( ENCRYPT_PADDING, result );
        }
        else if( revision == 3 || revision == 4 )
        {
            try
            {
                //STEP 2
                MessageDigest md = MessageDigest.getInstance("MD5");
                //md.update( truncateOrPad( password ) );
                md.update( ENCRYPT_PADDING );

                //STEP 3
                md.update( id );
                result.write( md.digest() );

                //STEP 4 and 5
                byte[] iterationKey = new byte[ encryptionKey.length ];
                for( int i=0; i<20; i++ )
                {
                    System.arraycopy( encryptionKey, 0, iterationKey, 0, iterationKey.length );
                    for( int j=0; j< iterationKey.length; j++ )
                    {
                        iterationKey[j] = (byte)(iterationKey[j] ^ i);
                    }
                    rc4.setKey( iterationKey );
                    ByteArrayInputStream input = new ByteArrayInputStream( result.toByteArray() );
                    result.reset();
                    rc4.write( input, result );
                }

                //step 6
                byte[] finalResult = new byte[32];
                System.arraycopy( result.toByteArray(), 0, finalResult, 0, 16 );
                System.arraycopy( ENCRYPT_PADDING, 0, finalResult, 16, 16 );
                result.reset();
                result.write( finalResult );
            }
            catch( NoSuchAlgorithmException e )
            {
                throw new CryptographyException( e );
            }
        }
        return result.toByteArray();
    }

    /**
     * This will compute the encrypted key.
     *
     * @param password The password used to compute the encrypted key.
     * @param o The owner password hash.
     * @param permissions The permissions for the document.
     * @param id The document id.
     * @param revision The security revision.
     * @param length The length of the encryption key.
     *
     * @return The encryption key.
     *
     * @throws CryptographyException If there is an error computing the key.
     */
    public final byte[] computeEncryptedKey(
        byte[] password,
        byte[] o,
        int permissions,
        byte[] id,
        int revision,
        int length )
        throws CryptographyException
    {
        byte[] result = new byte[ length ];
        try
        {
            //PDFReference 1.4 pg 78
            //step1
            byte[] padded = truncateOrPad( password );

            //step 2
            MessageDigest md = MessageDigest.getInstance("MD5");
            md.update( padded );

            //step 3
            md.update( o );

            //step 4
            byte zero = (byte)(permissions >>> 0);
            byte one = (byte)(permissions >>> 8);
            byte two = (byte)(permissions >>> 16);
            byte three = (byte)(permissions >>> 24);

            md.update( zero );
            md.update( one );
            md.update( two );
            md.update( three );

            //step 5
            md.update( id );
            byte[] digest = md.digest();

            //step 6
            if( revision == 3 || revision == 4)
            {
                for( int i=0; i<50; i++ )
                {
                    md.reset();
                    md.update( digest, 0, length );
                    digest = md.digest();
                }
            }

            //step 7
            if( revision == 2 && length != 5 )
            {
                throw new CryptographyException(
                    "Error: length should be 5 when revision is two actual=" + length );
            }
            System.arraycopy( digest, 0, result, 0, length );
        }
        catch( NoSuchAlgorithmException e )
        {
            throw new CryptographyException( e );
        }
        return result;
    }

    /**
     * This algorithm is taked from PDF Reference 1.4 Algorithm 3.3 Page 79.
     *
     * @param ownerPassword The plain owner password.
     * @param userPassword The plain user password.
     * @param revision The version of the security.
     * @param length The length of the document.
     *
     * @return The computed owner password.
     *
     * @throws CryptographyException If there is an error computing O.
     * @throws IOException If there is an error computing O.
     */
    public final byte[] computeOwnerPassword(
        byte[] ownerPassword,
        byte[] userPassword,
        int revision,
        int length )
        throws CryptographyException, IOException
    {
        try
        {
            //STEP 1
            byte[] ownerPadded = truncateOrPad( ownerPassword );

            //STEP 2
            MessageDigest md = MessageDigest.getInstance( "MD5" );
            md.update( ownerPadded );
            byte[] digest = md.digest();

            //STEP 3
            if( revision == 3 || revision == 4)
            {
                for( int i=0; i<50; i++ )
                {
                    md.reset();
                    md.update( digest, 0, length );
                    digest = md.digest();
                }
            }
            if( revision == 2 && length != 5 )
            {
                throw new CryptographyException(
                    "Error: Expected length=5 actual=" + length );
            }

            //STEP 4
            byte[] rc4Key = new byte[ length ];
            System.arraycopy( digest, 0, rc4Key, 0, length );

            //STEP 5
            byte[] paddedUser = truncateOrPad( userPassword );


            //STEP 6
            rc4.setKey( rc4Key );
            ByteArrayOutputStream crypted = new ByteArrayOutputStream();
            rc4.write( new ByteArrayInputStream( paddedUser ), crypted );


            //STEP 7
            if( revision == 3 || revision == 4 )
            {
                byte[] iterationKey = new byte[ rc4Key.length ];
                for( int i=1; i<20; i++ )
                {
                    System.arraycopy( rc4Key, 0, iterationKey, 0, rc4Key.length );
                    for( int j=0; j< iterationKey.length; j++ )
                    {
                        iterationKey[j] = (byte)(iterationKey[j] ^ (byte)i);
                    }
                    rc4.setKey( iterationKey );
                    ByteArrayInputStream input = new ByteArrayInputStream( crypted.toByteArray() );
                    crypted.reset();
                    rc4.write( input, crypted );
                }
            }

            //STEP 8
            return crypted.toByteArray();
        }
        catch( NoSuchAlgorithmException e )
        {
            throw new CryptographyException( e.getMessage() );
        }
    }

    /**
     * This will take the password and truncate or pad it as necessary.
     *
     * @param password The password to pad or truncate.
     *
     * @return The padded or truncated password.
     */
    private final byte[] truncateOrPad( byte[] password )
    {
        byte[] padded = new byte[ ENCRYPT_PADDING.length ];
        int bytesBeforePad = Math.min( password.length, padded.length );
        System.arraycopy( password, 0, padded, 0, bytesBeforePad );
        System.arraycopy( ENCRYPT_PADDING, 0, padded, bytesBeforePad, ENCRYPT_PADDING.length-bytesBeforePad );
        return padded;
    }
}