Rating:
# Sora (226 solves)
> This obnoxious kid with spiky hair keeps telling me his key can open all doors. Can you generate a key to open this program before he does? Connect to `challenges.auctf.com 30004` Author: nadrojisk
check function:
```c++
__int64 check(char *input)
{
int i;
for ( i = 0; i < strlen(secret); ++i )
{
if ( (8 * input[i] + 19) % 61 + 65 != secret[i] )
return 0;
}
return 1;
}
```
### Solution:
I wrote keygen for this challenge:
```python
from z3 import *
import sys
secret = 'aQLpavpKQcCVpfcg'
flag_len = len(secret)
def find_all_posible_solutions(s):
while s.check() == sat:
model = s.model()
block = []
out = ''
for i in range(flag_len):
c = globals()['b%i' % i]
out += chr(model[c].as_long())
block.append(c != model[c])
s.add(Or(block))
print(out)
def main():
s = Solver()
for i in range(flag_len):
c = globals()['b%d' % i] = BitVec('b%d' % i, 32)
s.add(c > 32, c < 127)
s.add((8 * c + 19) % 61 + 65 == ord(secret[i]) )
find_all_posible_solutions(s)
if __name__ == "__main__":
sys.exit(main())
```
Submitting any of them will give the flag:
```bash
$ nc challenges.auctf.com 30004
Give me a key!
try_7o"%rea."0(G
auctf{that_w@s_2_ezy_29302}
```
