Robust steganography is a technique of hiding secret messages in images so that the message can be recovered after additional image processing. One of the most popular processing operations is JPEG recompression. Unfortunately, most of today's steganographic methods addressing this issue only provide a probabilistic guarantee of recovering the secret and are consequently not errorless. That is unacceptable since even a single unexpected change can make the whole message unreadable if it is encrypted. We propose to create a robust set of DCT coefficients by inspecting their behavior during recompression, which requires access to the targeted JPEG compressor. This is done by dividing the DCT coefficients into 64 non-overlapping lattices because one embedding change can potentially affect many other coefficients from the same DCT block during recompression. The robustness is then combined with standard steganographic costs creating a lattice embedding scheme robust against JPEG recompression. Through experiments, we show that the size of the robust set and the scheme's security depends on the ordering of lattices during embedding. We verify the validity of the proposed method with three typical JPEG compressors and the {\it Slack} instant messaging application. We benchmark its security for various embedding payloads, three different ways of ordering the lattices, and a range of Quality Factors. Finally, this method is errorless by construction, meaning the embedded message will always be readable.

翻译：鲁棒隐写术是一种将秘密信息隐藏在图像中的技术，使得信息在经过额外图像处理后仍可被恢复。最常见的处理操作之一是JPEG再压缩。遗憾的是，当前大多数处理该问题的隐写方法仅提供恢复秘密信息的概率性保证，因此并非无差错。这是不可接受的，因为如果信息被加密，即使是单个意外更改也可能导致整条消息无法读取。我们提出通过检查DCT系数在再压缩过程中的行为来构建鲁棒系数集合，这需要访问目标JPEG压缩器。具体方法是将DCT系数划分为64个非重叠格点，因为一次嵌入修改可能在再压缩过程中影响同一DCT块内的多个其他系数。随后，将鲁棒性与标准隐写代价相结合，构建出对JPEG再压缩鲁棒的格点嵌入方案。实验表明，鲁棒集的大小及方案的安全性取决于嵌入过程中格点的排序。我们使用三种典型JPEG压缩器及Slack即时通讯应用验证了所提方法的有效性。针对不同嵌入负载、三种格点排序方式及一系列质量因子，我们对其安全性进行了基准测试。最后，该方法在结构上保证了无差错性，即嵌入的消息始终可读。