# Counter Mode: how to choose the nonce part of the counter? [duplicate]

Suppose:

• The "counter field" is about: NONCE || CTR-VALUE.
• I have multiples messages $M_a, M_b, M_c, \dots$
• Each message can be divided into x-bits blocks ($M_{a1}, M_{a2}, M_{a3}, \dots$).

1. Each message $M$ (for instance $M_a$) is encrypted following a randomly and uniquely generated key. In this case, does I really need the NONCE part of the "counter field" ?

2. If I really need a nonce, and knowing that each key is again unique-per-message, is there a secure way to derivate the nonce from the key ?