EncodedFileUtil.java

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/*
 * SleuthKit Java Bindings
 * 
 * Copyright 2011-2016 Basis Technology Corp.
 * Contact: carrier <at> sleuthkit <dot> org
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *     http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.sleuthkit.datamodel;

import java.io.IOException;
import java.io.RandomAccessFile;
import java.util.Arrays;

class EncodedFileUtil {
        
        final static private int HEADER_LENGTH = 32;  // All headers must be this long
        final static private String XOR1_HEADER =  "TSK_CONTAINER_XOR1_xxxxxxxxxxxxx";
        
        static String getHeader(TskData.EncodingType type) throws IOException{
                switch (type){
                        case XOR1:
                                return XOR1_HEADER;
                        default:
                                throw new IOException("Can not get header for " + type.toString());
                }
        }
        
        static byte [] getEncodedHeader(TskData.EncodingType type) throws IOException{
                if(type.equals(TskData.EncodingType.NONE)){
                        throw new IOException("Can not get encoded header for " + type.toString());
                }
                byte [] encHeader = new byte[HEADER_LENGTH];
                byte [] plainHeader = getHeader(type).getBytes();

                for(int i = 0;i < HEADER_LENGTH;i++){
                        encHeader[i] = encodeByte(plainHeader[i], type);
                }
                return encHeader;
        }
        
        static int getHeaderLength(){
                return HEADER_LENGTH;
        }
        
        static byte encodeByte(byte b, TskData.EncodingType type) throws IOException{
                switch (type){
                        case XOR1:
                                return ((byte)(b ^ 0xca)); 
                        default:
                                throw new IOException("Can not encode byte with encoding type " + type.toString());
                }
    }
        
        static byte decodeByte(byte b, TskData.EncodingType type) throws IOException{
                switch (type){
                        case XOR1:
                                return ((byte)(b ^ 0xca)); 
                        default:
                                throw new IOException("Can not decode byte with encoding type " + type.toString());
                }
    }   
        
        static TskData.EncodingType getEncoding(RandomAccessFile fileHandle){
                try{
                        long curOffset = fileHandle.getFilePointer();
                        if (curOffset != 0) {
                                fileHandle.seek(0);
                        }
                        byte[] header = new byte[HEADER_LENGTH];
                        int bytesRead = fileHandle.read(header, 0, HEADER_LENGTH);
                        if(bytesRead != HEADER_LENGTH){
                                return TskData.EncodingType.NONE;
                        }

                        return(getTypeFromHeader(header));
                } catch (IOException ex){
                        return TskData.EncodingType.NONE;
                }
        }
        
        static private TskData.EncodingType getTypeFromHeader(byte[] header){
                if(header.length != HEADER_LENGTH){
                        return TskData.EncodingType.NONE;
                }
                
                if(Arrays.equals(header, XOR1_HEADER.getBytes())){
                        return TskData.EncodingType.XOR1;
                } else {
                        return TskData.EncodingType.NONE;
                }
                
        }
}