-
Notifications
You must be signed in to change notification settings - Fork 7
New issue
Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.
By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.
Already on GitHub? Sign in to your account
Request for a writeup - CTF HXP 2019 - nacht #1
Comments
Hi, Here is the long-awaited reply. Sorry for being so late. First of all, you noticed that we have Your plan of solving
I hope this is useful to you. There are also some writeups from other teams on CTFtime. |
thx for your respons, I realized on one of the solutions i had to use the ideal of a PolynomialRing to find the correct C1 and C2. In my case i dont have any experience with this and thats why i kept stuck. Your insight on step 2 was a good one, i didnt knew i could transform it like that. |
Hello sir,
Could you make a writeup about the "nacht" CTF? I saw you solved it at "2019-12-29 18:00". Congrats
I manage get myself to get the X, A, R, S.
But my problem was getting the C1 and C2 in the formula:
X + S mod 2^128 = A
(C1 * R) + (C2 * R * R) mod (2^130 - 5) = X
I Re-arrange the formula:
R(C1 + C2 * R) = R * Y
R * Y * X mod (2^130 - 5) = 1
Then us modulo multiple inverse to find Y. But the Y i found is not the correct one.
If i could find the corrrect Y for two tag (A) cases i could find C1 and C2:
C2 = abs(Y1 - Y2) / abs(R1 - R2)
C1 = Y1 - (C2 * R1)
Happy 2020!
CTF: https://2019.ctf.link/internal/challenge/5af3da6e-8187-43cf-bd40-5f553e1a7a58
The text was updated successfully, but these errors were encountered: