Re: make one symmetric key of two symmetric keys

For example, one node has two symmetric keys ()K1, K2) shared with
another node; both nodes combine these keys to one key K3 (symmetric).
Assume that K1 is exposed by an adversary in some way, I want to send
out a new key K4 to the nodes, and the new key K5 is a combination of
K2 and K4. But how do a combine K2 and K4, can I use XOR or any hash
function to combine two keys to one in a secure way?

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