from flag import flag
assert flag.startswith("flag{")
assert flag.endswith("}")
assert len(flag)==24
def lfsr(R,mask):
output = (R << 1) & 0xffffff
i=(R&mask)&0xffffff
lastbit=0
while i!=0:
lastbit^=(i&1)
i=i>>1
output^=lastbit
return (output,lastbit)
def single_round(R1,R1_mask,R2,R2_mask,R3,R3_mask):
(R1_NEW,x1)=lfsr(R1,R1_mask)
(R2_NEW,x2)=lfsr(R2,R2_mask)
(R3_NEW,x3)=lfsr(R3,R3_mask)
return (R1_NEW,R2_NEW,R3_NEW,(x1*x2)^((x2^1)*x3))
R1=int(flag[5:11],16)
R2=int(flag[11:17],16)
R3=int(flag[17:23],16)
assert len(bin(R1)[2:])==17
assert len(bin(R2)[2:])==19
assert len(bin(R3)[2:])==21
R1_mask=0x10020
R2_mask=0x4100c
R3_mask=0x100002
for fi in range(1024):
print fi
tmp1mb=""
for i in range(1024):
tmp1kb=""
for j in range(1024):
tmp=0
for k in range(8):
(R1,R2,R3,out)=single_round(R1,R1_mask,R2,R2_mask,R3,R3_mask)
tmp = (tmp << 1) ^ out
tmp1kb+=chr(tmp)
tmp1mb+=tmp1kb
f = open("./output/" + str(fi), "ab")
f.write(tmp1mb)
f.close()
