Some thoughts, hope this helps:
The cipher is 1 character longer than the plaintext. This could suggest one of these (also other possibilities I didn't think of):
- The cipher relies on some state, that you initialize and then update each time a character is produced, for example start with $st=145$ and then at each step you read $c$, output $st-c$ (works for 1st letter "B"), and update $st$ (tried a few things but didn't find something coherent for the second letter.
- The cipher is a block cipher, and they needed to pad the message to reach the block size. $78=2*3*13$ so the block size can be one of $2,3,6,13,26,39,78$.
I tried with size $2$, hence trying to decode "145 211" into "Be", it looks like "B" is $211-145$ and "e" is $145+211$ (everything done mod 255), but this doesn't give anything for second couple of chars.
After a bit more analysis, the frequencies of couples in the cipher and plaintext do not match. They could match for blocksize 3, so i tried to find a matrix that would map the first 9 plaintext chars to first 9 ciphertext chars, but can't conclude because the system is not invertible