dc2019q - chainedrsa
This was a jeopardy challenge, part of dc2019q. (CTFtime)
Was solved by: 10 teams
Read carefully. Messages speak.
Hint 1Could publishing the upper half of an RSA decryption exponent be bad? Maybe there's a paper on that...
Hint 2Check the public key header -- what format is it?
Hint 3It's PKCS#1.2
Hint 4You need to make some changes and some optimizations, but you can skip some. On a regular laptop, it should be possible to complete in 3 minutes.
If you wish, you can contribute more.