I know that there are approximately 2^88 different permutations of 26 characters. The stream cipher A5/1, which generates a binary keystream using three irregularly clocked LFSR, and has a 64-bit key.
If we consider 1 000 characters of English text encrypted using either a substitution cipher or encoded in ASCII and encrypted using A5/1. From which ciphertext is it easiest to guess the plaintext?
In my opinion, the Substitution cipher is easy to guess. In the substitution cipher, it has repeated characters in the cipher-text make easier to figure out the text. Also, the substitution cipher has 26! possibilities. Can someone explain it to me in a more detail way?