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documenting 2 keys outputing the same first 6 bytes

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Sam Hadow 2024-04-24 09:55:49 +02:00
parent a7ea96648d
commit 49a9762802
1 changed files with 69 additions and 9 deletions
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78
main.py
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@ -87,7 +87,7 @@ def css_encrypt(text, key):
def test_encrypt():
print("test encryption: text 0xffffffffff, key 0x0 ∈ {0, 1}^40")
cipher = int.from_bytes(css_encrypt(0xffffffffff, [0]*40), byteorder='big')
cipher = int.from_bytes(css_encrypt(0xffffffffff, [0]*40))
print(f'cipher: {hex(cipher)}')
clear = int.from_bytes(css_encrypt(cipher, [0]*40))
print(f'decrypted: {hex(clear)}')
@ -167,29 +167,89 @@ def attack(Bytes=gen_6_bytes()):
for process in processes:
process.join()
while not result_queue.empty():
key = result_queue.get()
print(f'key found: \t{key}')
return [int(bit) for bit in key]
key = result_queue.get()
print(f'key found: \t{key}')
return [int(bit) for bit in key]
def test_attack(n=1):
success = 0
print(f'testing attack in 2^16 against CSS {n} times (keys randomly generated each time)\n')
for _ in range(n):
key = [randint(0, 1) for _ in range(40)]
# key = [1]*40
key_string = ''.join(str(bit) for bit in key)
print(f'key generated: \t{key_string}')
Bytes = gen_6_bytes(key)
found_key = attack(Bytes)
failed = []
if found_key == key:
success += 1
else:
failed.append(key)
print()
print(f'{success}/{n} success')
if len(failed)>0:
print("fails:")
for key in failed:
print("".join(str(bit) for bit in key))
def test_fail():
taps17 = [0, 14]
taps25 = [0, 3, 4, 12]
key = [1, 0, 1, 0, 1, 1, 0, 1, 0, 0, 1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 1, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 1]
key2 = [1, 0, 0, 0, 1, 1, 1, 0, 1, 1, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 1, 0, 1, 1, 0, 1, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 0]
print(f'both of these keys seem to output the same first 6 bytes, it only differs starting from byte 7:\n{"".join(str(bit) for bit in key)}\n{"".join(str(bit) for bit in key2)}\n')
lfsr17 = lfsr(key[:16]+[1], taps17)
lfsr172 = lfsr(key2[:16]+[1], taps17)
lfsr25 = lfsr(key[16:]+[1], taps25)
lfsr252 = lfsr(key2[16:]+[1], taps25)
x = []
y = []
x2 = []
y2=[]
for _ in range(7):
x_bin = ""
y_bin = ""
x_bin2 = ""
y_bin2 = ""
for _ in range(8):
x_bin += str(lfsr17.shift())
y_bin += str(lfsr25.shift())
x_bin2 += str(lfsr172.shift())
y_bin2 += str(lfsr252.shift())
x.append(int(x_bin[::-1], 2))
y.append(int(y_bin[::-1], 2))
x2.append(int(x_bin2[::-1], 2))
y2.append(int(y_bin2[::-1], 2))
print(f'LFSR outputs with 1st key: lfsr17: {x} lfsr25: {y}')
print(f'LFSR outputs with 2nd key: lfsr17: {x2} lfsr25: {y2}\n')
c = 0
c2 = 0
for i in range(7):
s = x[i]+y[i]+c
if s>255:
c=1
else:
c=0
s2 = x2[i]+y2[i]+c2
if s2>255:
c2=1
else:
c2=0
print(f'8bits addition at step {i} equal for both keys: {s%256}={s2%256} : {s%256==s2%256}')
text = 0xffffffffffff
cipher = int.from_bytes(css_encrypt(text, key))
cipher2 = int.from_bytes(css_encrypt(text, key))
print(f'\nencrypting 0xffffffffffff (6 bytes)\nwith 1st key: {hex(cipher)}\nwith 2nd key: {hex(cipher2)}\nboth outputs are equal: {cipher==cipher2}\n')
test_lfsr17()
print()
print("\n")
test_encrypt()
print()
test_attack(5)
print("\n")
# time to test attack with 100 keys
# CPU: 6 cores at 3.8GHz
# ~65 seconds
test_attack(10)
print("\n")
test_fail()