PDF steganography based on Chinese Remainder Theorem

We propose different approaches of PDF file based steganography, essentially based on the Chinese Remainder Theorem. Here, after a cover PDF document has been released from unnecessary characters of ASCII code A0, a secret message is hidden in it using one of the proposed approaches, making it invisible to common PDF readers, and the file is then transmitted through a non-secure communication channel. Each of our methods tries to ensure the condition that the number of inserted A0 is less than the number of characters of the secret message s.