## SECCON: Decrypt it
----------## Challenge details| Contest        | Challenge     | Category  | Points ||:---------------|:--------------|:----------|-------:|| SECCON | Decrypt it | Crypto | 300  |
*Description*>$ ./cryptooo SECCON{*************************}
>Encrypted(44): waUqjjDGnYxVyvUOLN8HquEO0J5Dqkh/zr/3KXJCEnw=
>what's the key?
----------## Write-up
If we do something like:
>```>./cryptooo SECCON\{>Encrypted(12): waUqjjDGnQ==>```
We can see that we already have the "waUqjjDGn" part right, this means we should be able to slowly extend the flag until we reach the encrypted flag.
I used bash commands like
>```>reset; for i in SECCON\{{{A..z},{0..9}}; do echo $i; ./cryptooo $i; done>```
in the beginning to slowly increase the message, however a pattern becomes appearant pretty fast and you can just check if the expected letters fit in, there is just one stray 1 in there.
After a while the flag is found:
>```>$ for i in SECCON\{Cry_Pto_Oo_Oo1Oo_oo_Oo_{O,o,0}\}; do echo $i; ./cryptooo $i; done>SECCON{Cry_Pto_Oo_Oo1Oo_oo_Oo_O}>Encrypted(44): waUqjjDGnYxVyvUOLN8HquEO0J5Dqkh/zr/3KXJCEnw=>SECCON{Cry_Pto_Oo_Oo1Oo_oo_Oo_o}>Encrypted(44): waUqjjDGnYxVyvUOLN8HquEO0J5Dqkh/zr/3KXJCMj8=>SECCON{Cry_Pto_Oo_Oo1Oo_oo_Oo_0}>Encrypted(44): waUqjjDGnYxVyvUOLN8HquEO0J5Dqkh/zr/3KXJCbUM=>```
Making the flag:
>```>SECCON{Cry_Pto_Oo_Oo1Oo_oo_Oo_O}>```