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Remove TODO about single-key caveats, and generalize to non-EC instances #11

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Apr 9, 2024
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Remove TODO about single-key caveats, and generalize to non-EC instances #11

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Remove TODO about single-key caveats, and generalize to non-EC instances
emlun Apr 4, 2024
45a8889
Merge branch 'main' into review-2024-04-03/bl-kem-same-key
emlun Apr 8, 2024
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17 changes: 8 additions & 9 deletions draft-bradleylundberg-cfrg-arkg.md
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Expand Up @@ -593,15 +593,15 @@ KEM-Decaps(sk, c) -> k
[^also_reject_g]{:emlun}


## Using both elliptic curve arithmetic for key blinding and ECDH as the KEM {#blinding-kem-ecdh}
## Using the same key for both key blinding and KEM {#blinding-kem-same-key}

If elliptic curve arithmetic is used for key blinding and ECDH is used as the KEM,
as described in the previous sections,
then both of them MAY use the same curve or MAY use different curves.
If both use the same curve, then it is also possible to use the same public key
as both the key blinding public key and the KEM public key. [Frymann2020]

[^same_key_caveats]{:emlun}
When an ARKG instance uses the same type of key for both the key blinding and the KEM -
for example, if elliptic curve arithmetic is used for key blinding as described in {{blinding-ec}}
and ECDH is used as the KEM as described in {{kem-ecdh}} [Frymann2020] -
then the two keys MAY be the same key.
Representations of such an ARKG seed MAY allow for omitting the second copy of the constituent key,
but such representations MUST clearly identify that the single constituent key is to be used
both as the key blinding key and the KEM key.


## Using HMAC as the MAC {#mac-hmac}
Expand Down Expand Up @@ -852,4 +852,3 @@ TODO

[^also_reject_g]: ISSUE: Also reject point G?
[^also_reject_1]: ISSUE: Also reject scalar 1?
[^same_key_caveats]: ISSUE: Caveats? I think I read in some paper or thesis about specific drawbacks of using the same key for both.
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