Theoretical security of bit rotation for encyption
Let's say the plaintext is English text (or some language that uses the basic latin characters), encoded in Unicode.  That means each byte represents one character, and because of the quirks of Unicode, the basic latin characters and typical punctuation marks all have a zero for the most significant bit.

To attack your scheme, an attacker would look for runs of bytes which all had zeros in the same bit-position.  A run of $x$ bytes all with a zero in the $y$ bit-position would suggest both a length for $n$ (something less than or equal to $x$) and also a rotation amount (the amount required to move the most significant zero bit to position $y$).

Even if the plaintext is not English text, or doesn't use Unicode, in your scheme the ciphertext still trivially leaks the parity of each byte of the plaintext (i.e. how many 1's and 0's are each byte), which is an atrocious amount of information to leak.  For a cipher to be secure, the ciphertext shouldn't leak any information whatsoever about the plaintext, except for its length.