CG-CTF single

1. Drag it into ida and analyze it statically first.

There are three functions. Click to see when

a1 is 0. When a2 [i] is 0, assign its own value to this position. When a1 is 0, you do n’t need it. move.


These three functions all imply that this thing is Sudoku. Each row and column has a number from 1 to 9 and cannot be repeated. . .
Take out the previous number, operate it with an online array solver

and write a script at the same time, change the place that was not zero to 0, which is the flag

shudu=[0x00, 0x03, 0x00, 0x06, 0x00, 0x00, 0x00, 0x00, 0x00, 0x06, 0x00, 0x00, 0x00, 0x03, 0x02, 0x04, 0x09, 0x00, 0x00, 0x09, 0x00, 0x01, 0x00, 0x07, 0x00, 0x06, 0x00, 0x07, 0x04, 0x06, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x08, 0x00, 0x00, 0x00, 0x06, 0x03, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x04, 0x07, 0x00, 0x08, 0x00, 0x09, 0x00, 0x04, 0x00, 0x07, 0x00, 0x00, 0x07, 0x04, 0x02, 0x01, 0x00, 0x00, 0x00, 0x06, 0x00, 0x00, 0x00, 0x00, 0x00, 0x03, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00]
for i in range(9):
  for j in range(9):
    print(str(int(shudu[9*i+j]))+" ",end="")
  print("")
flag="431695728657832491892147365746321589518479632923586147185964273374218956269753814"
trueflag=""
for i in range(9):
  for j in range(9):
    if shudu[9*i+j]!=0:
      trueflag+="0"
    else:
      trueflag+=flag[9*i+j]
print(trueflag)