Send License
Category: Web security
50 points
We have bought a service but unfortunately we lost the license key of it we are willing to give you a flag at the exchange of the key. From what we remember it was based on windows 95 oem algorithm.
We bought the service at july 3rd of 1999. send you’r keys here: http://IP:3000/?license=
Link: https://ch1.sbug.se
Solution
I’ve done some research how the win95 OEM keys were generated. Here’s the summary:
- first three digits have range
001-366and reflects the day of the year, - next two digits have range
95-03and reflects the year (1995-2003), - then
OEMstring goes in, - next digit has to be
0, - the modulo 7 of sum of the next six digits has to be equal 0, beside this, last one of the six has to be from
range
1-8, - next 5 digits can be really anything.
The format of the key is 00000-OEM-0000000-00000.
I’ve prepared 18499-OEM-0664595-82487 key which satisfies all above + requirements from challenge description.
Going to https://ch1.sbug.se/?license=18499-OEM-0664595-82487 gave the flag.
Flag
SBCTF{CR4CK1NG_95_W4S_N0T_TH4T_H4RD}