2. The basic idea of steganography for HEVC/H.265 video codec

Overview

In fact, for video steganography, image steganography or audio steganography, the basic idea is the same: read the original image (audio) -> select the carrier to be steganographic -> use the steganography method to steganize it- > Generate steganographic image (audio) -> Extract secret information -> Compare with embedded information.

1. The basic idea of ​​video steganography

The steganography method using the HEVC video codec is basically similar to the above process, which is mainly divided into four parts:
1. Use encoder 1, extract the selected original carrier information in encoder 1, and export it Save (original_cover)
2. Write a steganographic program externally (such as python or C++), import the original_cover information into the program, and embed the secret information (original_msg) according to the steganographic process to obtain the secret carrier after the steganography is completed (Stego_cover)
3. Send the secret carrier information back to Encoder 2, and use Encoder 2 to "encrypt the video" to get the secret video (stego.yuv)
4. Put the secret video into the decoder, Extract the secret information (extract_msg) and compare it with the previously embedded secret information (original_msg) to verify whether the embedded and extracted information is consistent.

2. Examples of video steganography

To give an example, use the LSB method to steganography the intra prediction mode of the intra prediction process:
1. In the correlation function of HM_1, extract all the intra prediction modes, export them, and save them as an original_IPM.txt
2 、In the external steganography program (.py), import the original_IPM.txt file and convert it into a binary stream file (original_IPM_binary.txt), according to the method of LSB steganography, embed the original_msg.txt information into original_IPM_binary .txt, get the secret carrier (stego_IPM.txt)

3. In the related function of HM_2, return all the steganographic intra prediction modes, and encode according to them to obtain the encrypted video.
4. Put the encrypted video into the decoder HM_3, in the corresponding function Save and export all intra-frame prediction modes (stego_IPM.txt), and convert them into a binary stream (stego_IPM_binary.txt), extract the secret information (extract_msg.txt) according to the LSB extraction method, and save the extracted hidden information (extract_msg.txt). Confidential information is compared with embedded secret information

3. End

This four-step video steganography method is universal in theory.
Compared with directly modifying the carrier information in the encoder, this method is more cumbersome and needs to find the function position of the effective information, but it is more universal, and the ready-made steganography method can be called in the external steganography program (For example, STC tool library).

In the next blog, we will record in detail the whole process of steganography of intra prediction mode using LSB method, including all information storage, steganography process, return process and problems encountered in the experiment.