The use of steganography to transmit secret data is becoming increasingly common in security products and malware today. Despite being extremely popular, PDF files are not often the focus of steganography research, as most applications utilize digital image, audio, and video files as their cover data. However, the PDF file format is promising for usage in medium-capacity steganography applications. In this paper, we present a novel PDF steganography algorithm based upon least-significant bit insertion into the real-valued operands of PDF stream operators. Where prior research has only considered a small subset of these operators, we take an extensive look at all the possible operators defined in the Adobe PDF standard to evaluate their usability in our steganography algorithm. We also provide a case study which embeds malware into a given cover PDF document.

翻译：隐写术在当今安全产品和恶意软件中传输秘密数据的应用日益普遍。尽管PDF文件极为普及，但其并非隐写术研究的主要关注对象，因为多数应用使用数字图像、音频和视频文件作为载体数据。然而，PDF文件格式在中容量隐写术应用中具有良好前景。本文提出一种新型PDF隐写算法，该算法基于PDF流运算符实值操作数的最低有效位嵌入技术。鉴于此前研究仅考虑了这些运算符中的一小部分，我们系统研究了Adobe PDF标准中定义的所有可能运算符，以评估其在本隐写算法中的可用性。此外，我们还通过案例研究展示了将恶意软件嵌入给定载体PDF文档的具体实施过程。