css encrypt

main.py

@@ -25,15 +25,15 @@ class lfsr(object):
         calculate next state and return the output bit
         '''
         feedback = sum(self.state[tap] for tap in self.taps) % 2
-        output = self.state[-1]
-        self.state = [feedback] + self.state[:-1]
+        output = self.state[0]
+        self.state = self.state[1:] + [feedback]
         return output
 
 
 def test_lfsr17():
     key = [randint(0, 1) for _ in range(16)] # first 16 bits
     key.append(1)  # prevent initial state from being {0}^17
-    taps = [16-0, 16-14]
+    taps = [0, 14]
     lfsr17 = lfsr(key, taps)
     states = [lfsr17.state]
     for _ in range(2**17-2):
@@ -49,4 +49,35 @@ def test_lfsr17():
     print(f'all {n_state} = 2^({n_state_log})-1 states are different')
     return True
 
+
+def css_encrypt(text, key):
+    taps17 = [0, 14]
+    lfsr17 = lfsr((key[:16]+[1]), taps17)
+    taps25 = [0, 3, 4, 12]
+    lfsr25 = lfsr((key[16:]+[1]), taps25)
+    cipher_text = 0
+    carry = 0
+    bytes = text.to_bytes((text.bit_length() + 7) // 8, 'big')
+
+    for byte in bytes:
+        x_b2 = ""
+        y_b2 = ""
+        # Generate bytes from lfsr17 and lfsr25
+        for _ in range(8):
+            x_b2 += str(lfsr17.shift())
+            y_b2 += str(lfsr25.shift())
+        x = int(x_b2, 2)
+        y = int(y_b2, 2)
+
+        z = (x + y + carry) % 256
+        carry = 1 if x + y > 255 else 0
+
+        cipher_byte = z ^ byte
+        cipher_text = (cipher_text << 8) | cipher_byte
+    return cipher_text
+
 test_lfsr17()
+cipher = css_encrypt(0xffffffffff, [0]*40)
+print(hex(cipher))
+clear = css_encrypt(cipher, [0]*40)
+print(hex(clear))