31Eki
LFSR, starting with a known sequence
Its known that cipher is made with LFRS. Cipher text is 868 bits long, and its known that the plaintext starts with "Dear Student", therefore we can get the keystream of first 84 bits. However, we do not know anything about the length of LFRS. I only know that if known portion of a plaintext has a length of 2m and the length of LFRS is m, we can solve m linear equations to get the the connection polynomial. In this example it's not given, so what is the right approach here to find the plaintext? Can anything be done with the acquired 84 bits, its linear complexity is 17 but does it really say anything about the whole keystream?
