Saiko Labs
A decompiled routine XORs the flag with a constant. Undo it.
Decompiled validator. The flag bytes are XOR'd with key 0x55:
char key = 0x55;
unsigned char enc[] = { 0x26, 0x34, 0x3c, 0x3e, 0x3a, 0x2e, 0x36, 0x27, 0x34, 0x36, 0x3e, 0x0a, 0x21, 0x3d, 0x30, 0x0a, 0x36, 0x3d, 0x30, 0x36, 0x3e, 0x26, 0x20, 0x38, 0x28 };
for (int i = 0; i < sizeof(enc); i++) putchar(enc[i] ^ key);