Abstract: Aims at the prevalent PDF documents, this paper proposes a novel steganography algorithm. Firstly, it points out the secret channels in the PDF documents. Then, it describes the algorithm which is integrated with several strategies that are applied to improve security. The algorithm makes use of redundancy to complement security, and constitutes a chaotic map to meet the Kerckhoffs principle. The analysis and experimental results show that this algorithm is efficient that can embed data of unlimited length into PDF documents and the embedded PDF documents keep transparency when being displayed in PDF readers.

Key words: PDF Documents; Steganography algorithm; Secret channel; Kerckhoffs principle

摘要： 目前应用极为广泛的PDF 文档，发现了其中存在可以用作信息隐写的隐密信道。通过采用以一定的冗余换取安全性的策略，并使用基于混沌模型的随机选择隐写单元的方法，使隐写系统满足Kerckhoffs 原理。分析和实验结果表明，该文隐写方法可嵌入任意大小的信息，并保持在PDF 阅读器中显示的透明性，具有较好的简单实用性。

关键词: PDF 文档；隐写术；隐密信道；Kerckhoffs 原理