It seems that the URI rules are changed

[boyang9602]

Unblurred is /html/bg1.png Blurred is /html/pages/blurred/page2.webp

[danieltyukov]

@boyang9602 interesting observation, I am a little busy currently could you perhaps check if you can adjust it and implement it and make a PR request and I will test it and approve it? and reference you in the next release.

[boyang9602]

Thanks, I will try it

[danieltyukov]

@boyang9602 any luck?

[boyang9602]

Hi, I investigated it a bit, however I do not have a full solution. First, for the pictures, what I have mentioned above should work. However, for the documents that contains text, I do not know how to unblur the texts.

I can share some findings.

The first example is https://www.studocu.com/en-ca/document/concordia-university/introduction-to-semiconductor-materials-and-devices/midterm-2/55562380?origin=course-trending-2. Where the first unblurred picture url is (I breakdown the parameters in different rows)

https://d3tvd1u91rr79.cloudfront.net/9797ea638f6c34a7aa900e571895c52c/html/bg1.png?
Policy=eyJTdGF0ZW1lbnQiOlt7IlJlc291cmNlIjoiaHR0cHM6XC9cL2QzdHZkMXU5MXJyNzkuY2xvdWRmcm9udC5uZXRcLzk3OTdlYTYzOGY2YzM0YTdhYTkwMGU1NzE4OTVjNTJjXC9odG1sXC8qLnBuZyIsIkNvbmRpdGlvbiI6eyJEYXRlTGVzc1RoYW4iOnsiQVdTOkVwb2NoVGltZSI6MTcxMjM1MTEwOX19fV19
&Signature=DG-Sfyx0tGmrOlDaCQBr8hmJZyg6YwCJJ~pTSMGKlGELDozA0H1Upcw7kt-JVtoFED7QEDp--j5aF-fblH3h9AfcZXDe0BhpwOMQblFO1Oy3FXCZPl440hmlohKsWkhy0I8SmZ~KI3GdJfThh6xNvktYJRLgElVUHPCyjfn4AvJjxFmOeEldKqfNcKVDN9NJSB3irwOIfJTETfu6KOiZIO70P5SjU8ukaop5L9Tg-SAOfNp62tP2yUfwzibIXZJ4B5Z5eGoQFrtzi5XgVjciyq6JKz80iVaAV8vBg28JbN4oVhsQHZxKpJDKMrMd-A0hn~GlVZTbM2~vm~W9YqM23g__
&Key-Pair-Id=APKAJ535ZH3ZAIIOADHQ

The second blurred picture url is

https://d3tvd1u91rr79.cloudfront.net/9797ea638f6c34a7aa900e571895c52c/html/pages/blurred/page2.webp?
Policy=eyJTdGF0ZW1lbnQiOlt7IlJlc291cmNlIjoiaHR0cHM6XC9cL2QzdHZkMXU5MXJyNzkuY2xvdWRmcm9udC5uZXRcLzk3OTdlYTYzOGY2YzM0YTdhYTkwMGU1NzE4OTVjNTJjXC9odG1sXC9wYWdlc1wvYmx1cnJlZFwvKiIsIkNvbmRpdGlvbiI6eyJEYXRlTGVzc1RoYW4iOnsiQVdTOkVwb2NoVGltZSI6MTcxMjM1MTEwOX19fV19
&Signature=CV2LTqN2mzEG9~ZSRvqrOmnN7iqNZ7pRAkRMMotLJHsJ9YUZ2v3gV-WgX6sYAkfVVFercuvtn-zc945VCDvkU2rD6Wz2fFy4SrBlXOb8aFOfT671RgcK5pXjENp~t56GJVd7iA~bLTY7uKX0-cNDFKDhtIOqk8MZ4rq8xvPam5rtjedtcu~t5vNyw4LZGL~c8bDyYCB9S7A01Yt7scxrdAUsmKc-SKtVuCZKxIlsNALdJgij7mAA55RdjcGyBjpUWHMLq33k2IB2pyPX4F-DcR~vp7fEVo44s4hqSucHNmj~4QabS3sJPyz8kXzyUgqe20iNHcS4Sb2-GhAw4J4U~w__
&Key-Pair-Id=APKAJ535ZH3ZAIIOADHQ

We can see that

1. The URI is different. The unblurred picture is /html/bg1.png, while the blurred is /html/pages/blurred/page2.webp.
2. The Policy and Signature are changed too.
3. The Key-Pair-Id keeps the same.

I tried to change the bg1 to bg2 in the first URL, and it is the unblurred second picture. So it indicates that the Policy and Signature for the unblurred pictures in the same document are the same. We can get them from any unblurred pictures. While the URI for the n-th picture is just /html/bg<n>.png. I verified this with other documents with more pages.

However, it seems that this is just a special case where there is no text.

I tried another case (link is provided below) which consists of both background picture and texts. The above findings still work for the background pictures, however, we still cannot see the texts above the background picture.

https://www.studocu.com/en-ca/document/concordia-university/optical-devices-for-high-speed-communications/elec425-assignment-1-solutions-explaining-how-the-question-from-assignment-1/19767622

Furthermore, by comparing the unblurred pictures of the two examples above, I found that Policy and Signatures for unblurred pictures are consistent for same document, but different for different document. Key-Pair-Id is the same for all the document.

In summary, I only find the rules for the pictures, but I do not have a solution for the blurred texts. I am busy recently and have not had a chance to further investigate it.

[danieltyukov]

Thanks a lot for the amazing documantion. I will thoroughly go through it after my exams in a week. Will notify you after pushing some updates based on this research and further research.

Thanks again.

[boyang9602]

Thank you! Good luck with your exams!