Is there an algorithm that gives a reasonable chance of decoding the entire ciphertext of this encryption scheme?
For a frequency-style solution, we can guess the least significant bytes of $k_1, k_2$, decrypt the least significant byte of each block, and check the frequency (e.g. space should be the most often). Then repeat with the previous byte, etc.
The scheme is bad in that it reduces to schemes mod $2^N$ for any $N &lt; n$.