xor64

problem

It was base64ed, but also XORed with… something?

AAAAABIFGFIOPBJWGw4VEjYFRBQ2FxwDNhRFCEg8VTlIPFU5SDxVOUg8VTlIPFU5SDxVGw==

solution

if we b64 decode it and then hexdump it, we can see that the flag is xored with ictf because ictf.* ^ (ictf)+ first four bytes are null bytes always due to the properties of xor

00000000: 0000 0000 1205 1852 0e3c 1256 1b0e 1512  .......R.<.V....
00000010: 3605 4414 3617 1c03 3614 4508 483c 5539  6.D.6...6.E.H<U9
00000020: 483c 5539 483c 5539 483c 5539 483c 5539  H<U9H<U9H<U9H<U9
00000030: 483c 551b                                H<U.

see it in tfw here