Saiko Labs
A decompiled routine XORs the flag with a constant. Undo it.
Decompiled validator. The flag bytes are XOR'd with key 0x33:
char key = 0x33;
unsigned char enc[] = { 0x40, 0x52, 0x5a, 0x58, 0x5c, 0x48, 0x50, 0x41, 0x52, 0x50, 0x58, 0x6c, 0x47, 0x5b, 0x56, 0x6c, 0x40, 0x4a, 0x40, 0x50, 0x52, 0x5f, 0x5f, 0x4e };
for (int i = 0; i < sizeof(enc); i++) putchar(enc[i] ^ key);