m0leCon 2021 CTF Teaser - Obscurity-fixed
Challenge
As before, but static!
Metadata
- Tags:
crypto - Author: mr96
- Points: 469
- Solves: 2
Solution
The algorithm resembles an FCSR, so I used the smallest FCSR algorithm by Klapper and Goresky. Using the bits just from the Look, a new flag: shown in the challenge script did not work, however adding the flag format, Look, a new flag: ptm{, got the flag.
The output of our solver script is the following:
> python solve.py
Period for 4 is 7
Period for 4 is 6
Period for 4 is 7
Period for 4 is 6
Period for 4 is 7
Period for 4 is 7
Period for 4 is 7
Period for 4 is 1
Period for 4 is 7
Period for 4 is 7
Period for 5 is 7
Period for 5 is 2
Period for 5 is 15
Period for 5 is 15
Period for 5 is 15
Period for 5 is 15
Period for 5 is 8
Period for 5 is 12
Period for 5 is 4
Period for 5 is 2
Period for 6 is 1
Period for 6 is 28
Period for 6 is 8
Period for 6 is 31
Period for 6 is 28
Period for 6 is 31
Period for 6 is 28
Period for 6 is 31
Period for 6 is 8
Period for 6 is 10
b'Look, a new flag: ptm'
-33653088377663776192109104 -50952268972205221877234096 -6658610176590470404853021 1036253257551142714799835
1036253257551142714799835 35
Built fcsr
b'Look, a new flag: ptm{n0w_r3p0r7_7h3_53c0nd_un1n73nd3d_70_@mr96_1cdf85df0860893c}'
The flag is ptm{n0w_r3p0r7_7h3_53c0nd_un1n73nd3d_70_@mr96_1cdf85df0860893c}.