I searched in google about the generation of `windows 95 oem key` Keys have the pattern **XXXXX-OEM-XXXXXXX-XXXXX**
The first part is 3 first digits are the day of the year and the 2 last are the year (95-03)
July 3rd was the 184th day of 1999 so the first part is 18499
The second part first digit is 0 and sum of the 6 more must be divisible by 7 I chose 0123456
Part 3 is just random numbers - unchecked
The key I used was 18499-OEM-0123456-11111 After going to http://ch1.sbug.se/?license=18499-OEM-0123456-11111 I got the flag
> SBCTF{CR4CK1NG_95_W4S_N0T_TH4T_H4RD}
**bonus** Win 95 had a lot of good keys and so there are to get the flag The exact number is 142880 * 10^5 = 14288000000 (from part 3 and 4)