ciphertext1 = hmac-sha256(key, counter1) ⊕ (plaintext1 with plaintext1 sha1 hash) ciphertext2 = hmac-sha256(key, counter2) ⊕ (plaintext2 with plaintext2 sha1 hash) ciphertext3 = hmac-sha256(key ,counter3) ⊕ (plaintext3 with plaintext3 sha1 hash) . . .
Note: counterN is increasing while (plaintextN with plaintextN sha1 hash) is longer than hmac-sha256(key, counterN). So it is a while function to continue hmac-sha256 with increased counters
Lets say Eve know counters and ciphertexts. Can Eve do anything other than bruteforce to find key? Is hiding counter from Eve necessary? Or can Eve break this cipher without key? What is the usage limit of this algorithm to continue use same key for hmac-sha256?
Note-2: I am not cryptographer. It is just curiosity
Note-3: key length is 256 bit