Using Steganography to hide messages inside PDF files

Steganography focuses on hiding information in such a way that the message is undetectable for outsiders and only appears to the sender and intended recipient. Portable Document Format (PDF) steganography has not received as much attention as other techniques like image steganography because of the lower capacity and text-based file format, which make it harder to hide data. However some approaches have been made in the field of PDF steganography. One of the current and most promising methods uses the TJ values, which are used to display text, in PDF files to hide data. The goal of the project was to improve the capacity and, if possible, the security of this method. The TJ method is therefore carefully analysed for weaknesses. In the process of doing this, an implementation of this method was developed. Statistical analyses of the TJ values showed that the TJ method is not very strong and that hidden data can easily be detected. Based on the results of the many experiments that were performed, two different algorithms were composed. The first one has a lower capacity but is more secure. The second one offers a much higher embedding capacity while it still keeps the same level of security. Both algorithms are proposed as an alternative for the original TJ method.