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There are two ways for key change: key update, and Re-keying. Which of these methods use a KDF (Key Derivation Function) for getting new keys?

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Both, as I recall they mean the same thing... –  user1028028 Feb 5 '14 at 13:22
Difference between re-keying and key update is , that in case of re-keying the new key is independent of old key, in case of key update key is depend of old key. –  Gev_sedrakyan Feb 5 '14 at 13:27
That would be bad ... as it might open the encryption to a related key attack... –  user1028028 Feb 5 '14 at 13:34
Key update can still be dependent on the old key, but not be related on a cipher level, as you can run it through a KDF or hash algorithm. Just as re-key can use purely random data and not go through a KDF, either one can use or not use a KDF –  Richie Frame Feb 5 '14 at 20:04

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