The cover image is generally encrypted by a stream cipher in existing reversible data hiding in encrypted image (RDHEI) methods. As pixel correlation is seriously damaged, more than one pixel should be employed to carry one bit such that the quite limited capacity is achieved. To overcome this issue, a new RDHEI method with high capacity, that preserves pixel correlation and exploits it to vacate embedding room, is proposed in this paper. First, we propose a block-level encryption scheme which combines block-level stream cipher and block-level permutation, and all blocks are classified into usable blocks (UBs) and unusable blocks (NUBs) by preserving the correlation of pixels in blocks. Then, UB is reconstructed to vacate room for data embedding, because the pixels in blocks share the same most significant bits (MSBs). To ensure reversibility, the number of NUBs between current UB and the previous one is also embedded along with additional data, and the blocks are rearranged in a reversible way such that UBs are always in front of NUBs. Experimental results show that not only the embedding capacity is significantly improved but also the hidden data can be losslessly extracted, and the cover image can be perfectly recovered.

中文翻译：

---

基于块内无损压缩的加密图像中隐藏的大容量可逆数据

在现有的加密图像中的可逆数据隐藏（RDHEI）方法中，封面图像通常通过流密码进行加密。由于像素相关性受到严重破坏，因此需要使用多个像素来承载一位，从而达到相当有限的容量。为了克服这个问题，本文提出了一种新的具有高容量的RDHEI方法，该方法可以保留像素相关性并利用它来腾出嵌入空间。首先，我们提出了一种块级加密方案，它结合了块级流密码和块级置换，通过保留块中像素的相关性，将所有块分为可用块（UB）和不可用块（NUB）。然后，重建 UB 以腾出空间用于数据嵌入，因为块中的像素共享相同的最高有效位 (MSB)。为确保可逆性，当前 UB 和前一个之间的 NUB 数量也与附加数据一起嵌入，并且块以可逆方式重新排列，使得 UB 始终位于 NUB 之前。实验结果表明，不仅嵌入容量显着提高，而且隐藏数据可以无损提取，覆盖图像可以完美恢复。