以不可见水印作为电子印花税票的附加取证特征

摘要

电子印花税票（e-meterai）是印度尼西亚政府由税务总局（DGT）发行的官方数字产品。随着传统文书日益转为数字形式，其使用范围不断扩大，作用与纸质印花税票相同。该产品以嵌有印尼专属编码的快速响应码为特征，并具备显性、隐性与取证三类特征。本研究旨在试验为其增加一项以不可见水印形式呈现的取证特征。本文采用离散傅里叶变换（DFT）与尺度不变特征变换（SIFT）两种水印嵌入技术，以判定何者更适合该应用。嵌入水印后，本文还模拟了高斯噪声、椒盐噪声、均值滤波、旋转、平移与斑点噪声等多种攻击。对每种攻击均计算归一化互相关（NCC）值：在DFT与SIFT技术下，高斯噪声攻击分别为0.863与0.976，椒盐噪声攻击分别为0.929与0.984，均值滤波攻击分别为0.975与0.984，旋转攻击分别为0.173与0.097，平移攻击分别为0.172与0.032，斑点噪声攻击分别为0.972与0.996。

Abstract

The e-meterai is an official digital product of the Indonesian government issued by the Directorate General of Taxation (DGT). Its usage has become increasingly widespread as conventional documentation transitions to digital formats, serving the same function as its printed counterpart. This product features a quick-response code embedded with unique Indonesian codes and offers overt, covert, and forensic features. This study aims to experiment with adding a forensic feature in the form of an invisible watermark. We employed two watermark embedding techniques, discrete Fourier transform (DFT) and scale-invariant feature transform (SIFT), to determine which is more suitable for this application. After embedding the watermark, we also simulate various attacks including gaussian noise, salt and pepper noise, averaging filter, rotation, translation, and speckle noise. For each attack, we calculated with normalized cross-correlation (NCC) values, obtaining 0.863 and 0.976 for the gaussian noise attack, 0.929 and 0.984 for the salt and pepper attack, 0.975 and 0.984 for the averaging filter attack, 0.173 and 0.097 for rotation attacks, 0.172 and 0.032 for translation attack, and 0.972 and 0.996 for speckle noise attack, using DFT and SIFT techniques, respectively.