sam.hadow/CSS-cipher
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attack in 2^16

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Sam Hadow 2024-04-22 19:08:27 +02:00
parent 71175c8ebd
commit 0c0ff62e1f
1 changed files with 54 additions and 3 deletions
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57
main.py
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@ -94,9 +94,9 @@ def test_encrypt():
print(f'original text and decrypted message are the same: {clear==0xffffffffff}') print(f'original text and decrypted message are the same: {clear==0xffffffffff}')
def gen_6_bytes(): def gen_6_bytes():
# key = [randint(0, 1) for _ in range(40)] key = [randint(0, 1) for _ in range(40)]
# key = [1, 1, 0, 0, 1, 1, 0, 1, 1, 0, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 1, 0, 1, 0, 1, 0, 1, 0, 0, 1, 0, 1, 0, 0, 1, 0, 0, 0, 0, 0] # key = [1, 1, 0, 0, 1, 1, 0, 1, 1, 0, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 1, 0, 1, 0, 1, 0, 1, 0, 0, 1, 0, 1, 0, 0, 1, 0, 0, 0, 0, 0]
key = [0]*40 # key = [0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 1]
text = b'\x00\x00\x00\x00\x00\x00' text = b'\x00\x00\x00\x00\x00\x00'
print(key) print(key)
cipher = css_encrypt(text, key) cipher = css_encrypt(text, key)
@ -104,8 +104,59 @@ def gen_6_bytes():
print(css_encrypt(cipher, key)) print(css_encrypt(cipher, key))
return cipher return cipher
def attack():
Bytes = gen_6_bytes()
taps17 = [0, 14]
taps25 = [0, 3, 4, 12]
# (2**16)-1
for i in range((2**16)-1):
lfsr17_init = [int(bit) for bit in bin(i)[2:].zfill(16)]+[1]
# print(lfsr17_init)
lfsr17 = lfsr(lfsr17_init, taps17)
x = []
for _ in range(3):
x_bin = ""
for _ in range(8):
x_bin += str(lfsr17.shift())
x.append(int(x_bin[::-1], 2))
y = [(Bytes[0]-x[0])%256]
c=1 if x[0]+y[0]>255 else 0
y.append((Bytes[1]-(x[1]+c))%256)
c=1 if x[1]+y[1]>255 else 0
y.append((Bytes[2]-(x[2]+c))%256)
lfsr25_init = [int(bit) for bit in (bin(y[0])[2:].zfill(8)[::-1] + bin(y[1])[2:].zfill(8)[::-1] + bin(y[2])[2:].zfill(8)[::-1] ) ]+[1]
# print(f'x: {x}, y: {y}')
# for b in Bytes:
# print(b, end=' ')
# print('\n')
# print(lfsr25_init)
lfsr25 = lfsr(lfsr25_init, taps25)
for _ in range(24):
lfsr25.shift()
for _ in range(3):
x_bin = ""
y_bin = ""
for _ in range(8):
x_bin += str(lfsr17.shift())
y_bin += str(lfsr25.shift())
x.append(int(x_bin[::-1], 2))
y.append(int(y_bin[::-1], 2))
c=1 if x[2]+y[2]>255 else 0
z4 = (x[3]+y[3]+c)%256
c=1 if x[3]+y[3]>255 else 0
z5 = (x[4]+y[4]+c)%256
c=1 if x[4]+y[4]>255 else 0
z6 = (x[5]+y[5]+c)%256
if z4 == Bytes[3] and z5 == Bytes[4] and z6 == Bytes[5]:
print("key found:")
key = bin(x[0])[2:].zfill(8)[::-1] + bin(x[1])[2:].zfill(8)[::-1] + bin(y[0])[2:].zfill(8)[::-1] + bin(y[1])[2:].zfill(8)[::-1] + bin(y[2])[2:].zfill(8)[::-1]
print(key)
break
test_lfsr17() test_lfsr17()
print() print()
test_encrypt() test_encrypt()
print() print()
gen_6_bytes() #gen_6_bytes()
attack()