Is IV needed in ECIES (Elliptic Curve Integrated Encryption Scheme) used with AES-CTR?

The ephemeral key pair is generated randomly therefore the encryption key derived from the public key must be random, too. As I know, IV is required only if the symmetric encryption key is used more than once, but in ECIES, every time an ephemeral key is generated, new encryption key is derived from that.

Am I right or IV is still recommended in ECIS w?


1 Answer 1


Pedantically, you always have an IV with AES-CTR; you need to start counting somewhere. So, your question really is "do I need an explicit IV, or can I use an implicit all-0 IV"?

With AES-CTR, the important requirement for IVs is that you never reuse the same IV for the same key. With ECIES, you'd reuse a key only if the sender used the same random number $r$ twice (and used that common $r$ to encrypt to the same public key). Assuming that you never do that, that is, you always pick a fresh $r$ whenever you do a public key encryption, then you are correct, using an implicit fixed IV is just fine.

  • $\begingroup$ Deleted my answer as this one was 3 minutes earlier and contains exactly the same information (including the fact that you always require a starting counter). $\endgroup$
    – Maarten Bodewes
    Jan 26, 2017 at 15:28

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