Bugku CTF daily one question chessboard with only black chess

Only the board of black chess

Opening is a flag.zip And a picture , The chessboard didn't understand the meaning , So I used it first winhex Open it and have a look
In the end, I found an exception

There should be a compressed package , But with binwalk The analysis has no result

After analyzing for a long time, I found that there was a prompt that it was repaired manually
Here is a knowledge point ：

zip The compressed package starts with 504B0304 start , It can be mixed with many 504B0102, Finally 504B0506 finishing 

Sure enough, there is a problem with the compressed package format , The first should be changed to 504B0304

Change after change zip Suffix will find that you need to enter a password , But there is no password prompt ？ Look at the attributes , No hints , There is no prompt for using the color tool , It suddenly occurred to me whether it was pseudo encryption ？ It's true

Change 09 by 00 Then I opened the compressed package and found a txt file , The contents of the document are as follows

…
…
CDEFGHIJKLMNOPQRSTU
BCDEFGHIJKLMNOPQRST
ABCDEFGHIJKLMNOPQRS

The discovery begins with C->B->A
And there are three ellipsis in front , After reading the prompt, I want us to complete the ten lines , Then match the pieces on the grid , It's really a little brain opening , After completion is the following , Press

JKLMNOPQRSTUVWXYZAB
IJKLMNOPQRSTUVWXYZA
HIJKLMNOPQRSTUVWXYZ
GHIJKLMNOPQRSTUVWXY
FGHIJKLMNOPQRSTUVWX
EFGHIJKLMNOPQRSTUVW
DEFGHIJKLMNOPQRSTUV
CDEFGHIJKLMNOPQRSTU
BCDEFGHIJKLMNOPQRST
ABCDEFGHIJKLMNOPQRS

Spread the letters on the chessboard , Press 1-10 Get the following letters in the order of
GOODGOPLAY
Namely flag.zip Unzip password for , After decompressing, it is found to be a picture
use winhex open , It's a standard picture , But there are PS Suspicion of modification

Try to change the height and width , As a result, the blind cat took the dead mouse , After heightening flag There was a little

So it's bigger , obtain flag