# Exploiting Online Services to Enable Anonymous and Confidential Messaging
## 3 Assessment of Online Content Sharing Services
Figure 2: Adopted base images: (**a**) solid colour; (**b**) airport; (**c**) baboon; (**d**) jellybeans. Imgur had a 100% success rate when using images with a resolution of 1920 \(\times\) 1080 pixels or less. Images with higher resolutions or in PNG format were converted to JPEG and compressed in such a way that their size became too small to retain the secret message. However, if the original image was already in JPEG format, the image file changes did not disrupt the steganography. Further, the secure hash results of the retrieved images were different from those of the uploaded pictures. After additional analysis, we concluded that Imgur stripped metadata from all images, resulting in different hash values for the same images. These conclusions were drawn by extracting the core data of the images and then comparing the secure hash values of these. Fickr had a 100% success rate due to the fact that Flickr allows the user to download the original images without any changes. Even image metadata and resolutions are preserved. The secure hash values of the downloaded images confirmed that no modifications were made to the uploaded images. ImgBox was able to retrieve information for all steganography programs except StegHide. In our testing, StegHide processed only JPEG images, which, in this case, underwent enough changes to disrupt steganography-based message retrieval. Table 5 summarizes the comparison of the tested online services with regard to file modification, image characteristic modification, and the capability of retrieving the hidden text from the downloaded images. Imgur alters the image files but does not alter the image data, as proven by different hash values of the files and equal hash values of the data section of the image. Imgur also enables the retrieval of hidden text unless the image resolution exceeds 1920 \(\times\) 1080 pixels. As a remark, Flickr and Imgur appear to adequately demonstrate the viability of the use of steganography. Image resolution should be 1920 \(\times\) 1080 pixels or lower. The PNG format offers more space to hide information but is also more likely to suffer compression and format change. The smallest image size used, 256 \(\times\) 256 pixels, was still able to hide a 256-character message. In particular, Imgur allows images to be uploaded anonymously, and images are also not listed on its website, so only users that have the URL or know the ID of an image can access it. Such behaviour, despite favouring anonymous operations, raised one problem: How would the receiver know the location of and get access to the image? The users should avoid at all costs sending the image links to each other, as this would lead to their identification. On the one hand, a specific service could be developed to exchange the image links. On the other hand, searching and evaluating existing online services is also an option. Multiple possibilities were identified, such as Advanced DontPad [32], Dontfile [33], Dontpad++ [34], and Dontpad [35]. Of these, only the latter operates solely in HyperText Markup Language (HTML), while the remaining ones require the execution of JavaScript (JS) in their text area. The use of JS was considered a limitation since it requires a client application to first render the page before being able to work with the data in it, increasing the use of resources and its runtime. Being an online text-file editor, DontPad is \begin{table}
\begin{tabular}{c|c c c|c c} \hline \hline  & **Facebook** & **LinkedIn** & **Twitter** & **Imgur** & **Flickr** & **ImgBox** \\ \hline OpenPuff & 0\% & 0\% & 0\% & 100\% & 100\% & 87.5\% \\ \hline OpenStego & 0\% & 0\% & 0\% & 100\% & 100\% & **100\%** \\ \hline StegHide & 0\% & 0\% & 0\% & 100\% & 100\% & 0\% \\ \hline StegoShare & 0\% & 0\% & 0\% & 100\% & 100\% & 100\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Percentage of successfully retrieved messages.