I would like to know what is the security of an encrypt-and-MAC with different keys for each transaction
For example: the one-time-pad with $k_1$ and the HMAC with $k_2$
$$C = M \oplus k_1\\ MAC = HMAC(k_2,M)$$
The ciphertext is $C||MAC$. The two keys $k_1$ and $k_2$ change for each transaction (for each $M$).