JAVA实现一个简易的图片防伪算法[课设]
图片防止篡改部分 第一步，获取图片的md5字符串，并转为字节数组 //将图片使用md5加密 private static byte[] img2Md5Bytes(File file,String salt) throws Exception{ FileInputStream inputStream=new FileInputStream(file); StringBuilder builder=new StringBuilder(); byte[] bytes=new byte[1024]; int bytesRead; while ((bytesRead=inputStream.read(bytes))!=-1){ builder.append(new String(bytes,0,bytesRead)); } inputStream.close(); builder.append(salt); String md5=md5(builder.toString()); return hexStringToBytes(md5); } //16进制转字节数组 private static byte[] hexStringToBytes(String hexString) { if (hexString == null || hexString.equals("")) { return null; } hexString = hexString.toUpperCase(); int length = hexString.length() / 2; char[] hexChars = hexString.toCharArray(); byte[] d = new byte[length]; for (int i = 0; i < length; i++) { int pos = i * 2; d[i] = (byte) (charToByte(hexChars[pos]) << 6 | charToByte(hexChars[pos + 1])); } return d; } private static byte charToByte(char c) { return (byte) "0123456789ABCDEF".indexOf(c); } //md5加密字符串 private static String md5(String str) { try { MessageDigest md = MessageDigest.getInstance("MD5"); md.update(str.getBytes()); return new BigInteger(1, md.digest()).toString(16); } catch (Exception e) { return ""; } } 第二步，图片末尾加md5字节数组 //图片末尾加md5字节数组 private static void imgAppendMd5Bytes(File file,byte[] md5Bytes) throws Exception{ RandomAccessFile accessFile=new RandomAccessFile(file,"rw"); long length=accessFile.length(); accessFile.seek(length); accessFile.write(md5Bytes); accessFile.close(); } 第三步，封装一下 //防止图片被篡改 private static void preventTamper(File file,String salt) throws Exception{ byte[] md5bytes=img2Md5Bytes(file,salt); imgAppendMd5Bytes(file,md5bytes); } 图片验证部分 第一步，获取图片的末尾存储的md5字节数组 //获取存储在图片末尾的16个md5字节 public static byte[] popMd5Bytes(File file) throws Exception{ RandomAccessFile accessFile=new RandomAccessFile(file,"rw"); byte[] bytes=new byte[16]; long length=accessFile.length(); accessFile.seek(length-16); for (int i=0;i<16;i++){ bytes[i]=accessFile.readByte(); } accessFile.close(); return bytes; } 第二步，去除图片末尾的16个md5字节后，重新计算图片的md5值 //去除图片末尾的16个md5字节 private static void imgDelEndMd5Bytes(File file) throws Exception{ RandomAccessFile accessFile=new RandomAccessFile(file,"rw"); FileChannel fc = accessFile.getChannel(); fc.truncate(accessFile.length()-16); fc.close(); accessFile.close(); } byte[] imgMd5=img2Md5Bytes(file,salt); 第三步，封装为方法 //验证图片是否被篡改 private static boolean notTamper(File file,String salt) throws Exception{ byte[] storageMd5=popMd5Bytes(file);//获取存储在图片末尾的16个md5字节 imgDelEndMd5Bytes(file);//删除末尾md5字节数组 byte[] imgMd5=img2Md5Bytes(file,salt); return Arrays.equals(storageMd5,imgMd5); } 简单实现，没有进行调优
