I was wondering if there were any security implications of deriving session keys from a symmetric key using SHA256 in the following manner: $Ks = SHA256(Nonce||K)$, where $Nonce$ is the session specific nonce and $K$ is the pre-shared symmetric key. And $Ks$ will be derived at both ends as mentioned.
As far as I am aware, length extension attacks are not applicable here as being able to append additional data to the input makes no difference. Would $Ks = HMAC(Nonce, K)$ be any different security-wise? What would be an advisable way of going about my requirement?