# Exploiting Online Services to Enable Anonymous and Confidential Messaging
## 3 Assessment of Online Content Sharing Services
The second test was designed to (1) determine if the compression algorithms used by the different services impacted the steganography; (2) assess if the systems maintain their behaviour when presented with images with different characteristics, such as lower resolutions or monochrome images; and (3) assess if the systems work when hiding bigger text messages. Thus, this test consisted of two specific text messages of different lengths encrypted with AES256 and hidden by a steganography application in four base test images of different colours and sizes. The first text message was \"The quick brown for jumps over the lazy dog\", and the second is a random 256-character message. The adopted base test images for the second test are presented in Figure 2 and consisted of a solid grey image with a resolution of 1920 \(\times\) 1080 pixels plus three other images from Volume 3 of the database of standard test images of the University of Southern California [31]. In particular, images \"4.1.08--Jellybeans\" (with a resolution of 256 \(\times\) 256 pixels), \"4.2.03--Baboon\" (with a resolution of 512 \(\times\) 512 pixels), and \"5.3.02--Airport\" (with a resolution of 1024 \(\times\) 1024 pixels) were selected due to their different resolutions and the need to have both coloured and grayscale images. All images were then converted to both PNG and JPEG formats due to the fact that some steganography programs only support one of these formats. To check the differences between the images before and after the upload to the online services, secure hashes (MD5 and SHA) were obtained and compared. The second test was conducted during the months of September and October of 2021, and a total of 192 image uploads was processed and analysed (6 online services, 4 steganography applications, and 8 images--the 4 selected images with the first text message and the same 4 with the second one). Table 4 shows the percentage of secret messages that were recovered after the respective image had been uploaded to and downloaded from an online service. The results show that when using Facebook, LinkedIn, and Twitter, no messages were recovered. The other services had success rates of 0%, 87.5%, and 100%. The Facebook, Twitter, and LinkedIn compression algorithms do not appear to be the same, since the hash values of all images were different. Further, all images, regardless of resolution, file size or format, were converted into JPG format, and the resulting file size was smaller. Images having a resolution of 3840 \(\times\) 2160 pixels were reduced to 2048 \(\times\) 1152 pixels on Facebook and LinkedIn. The metadata of the image was also changed. These social network platforms use image compression, directly hampering steganography. Similar behaviour was assumed to exist in all social network platforms. \begin{table}
\begin{tabular}{l l l l l l l l l} \hline \hline  & & \multicolumn{2}{c|}{**Input**} & \multicolumn{4}{c}{**Output Image**} \\ \cline{3-10}  & & **Stego Image** & **Facebook** & **Linkedin** & **Twitter** & **Insur** & **Flickr** & **ImgBox** \\ \hline \multirow{3}{*}{OpenPuff} & Size & 6.72 MB & 312 KB & 186 KB & 546 KB & 467 KB & 6.72 MB & 6.54 MB \\  & Res. & 3840 \(\times\) 2160 & 2048 \(\times\) 1152 & 2048 \(\times\) 1152 & 3840 \(\times\) 2160 & 3840 \(\times\) 2160 & 3840 \(\times\) 2160 & 3840 \(\times\) 2160 \\  & Format & PNG & JPG & JPG & JPG & JPG & PNG & PNG \\ \hline \multirow{3}{*}{OpenStego} & Size & 7.8 MB & 312 KB & 186 KB & 545 KB & 467 KB & 7.8 MB & 4.49 MB \\  & & & & & & & & \\  & & & & & & & & \\  & Format & PNG & JPG & JPG & JPG & PNG & PNG \\  & Size & 791 KB & 277 KB & 187 KB & 770 KB & 794 KB & 791 KB & 877 KB \\ \multirow{3}{*}{SegHide} & Res. & 3840 \(\times\) 2160 & 1920 \(\times\) 1080 & 2048 \(\times\) 1152 & 3840 \(\times\) 2160 & 3840 \(\times\) 2160 & 3840 \(\times\) 2160 \\  & Format & PNG & JPG & JPG & JPG & JPG & PNG & PNG \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Results of the first test.