MAC key definition
Examples of MAC key in a sentence
The insight is to use the MAC key before Auth begins.2 Our modification is beneficial for three reasons.
Because MACs work even when the key does not have full entropy, ▇▇▇▇▇ can simply choose a random balanced string for the MAC key k1 instead of choosing fully random k1, converting it to a balanced string for Auth, and then having Bob convert it back.
We improve this by encoding the message transmitted by Auth (namely, the MAC key k1) in base 4 rather than in base 2.
More precisely, let π be the security of the MAC for any fixed ∆, and α be the length of the MAC key.
Then the secret key SK is the just the MAC key μ, which has length κ =2 log n˜+3 log 1 +4 log 1 .
The MAC key, in turn, is used to authenticate the extrac- tor seed s (which can be done very efficiently using simple information-theoretic MACs).
Then the secret key SKExt is just the MAC key, whose length is 2 log n + 3 log 1 +4 log 1 +O(1) as long as d = O(n) and k = O(n) (which is the case with typical extractor and secure sketch constructions), so that n˜ = O(n).
In a later refinement of the technique, ▇▇▇▇▇▇▇ and ▇▇▇▇▇▇▇▇ [9] designed a MAC-based authenticator which uses a pre-existing shared secret as the MAC key.
GS verifies the signature, decapsulates the ciphertext, derives the MAC key and a session key and verifies the MAC tag.
At a high level, the reason why FREEK achieves a weaker guarantee is that some secrets used by id (the init secret and the MAC key) are shared among all group members.