Re: what is the size of a message encrypted with ECIES



Thanks for your answers guys, & thanks for the time spent answering.
I'm not really a mathematician, so I didn't understand fully what you described. I guess I still need much research understanding what ECC is about.
I guess I should try to describe more what I want to do. So the idea is that there is one application (which code won't change for years) set up with fixed parameters (the chosen elliptic curve, the chosen public key, etc...) which will send the messages (let's call it the client). One the other side, there will be the server (with similar parameters set up, including the private key). The size of the messages will always be the same. The client will be the only one sending messages, the server is only receiving (like sensors sending data for example).
The idea is that the protocol should be able to remain the same for decades, so that's why I want to choose the biggest key size to increase security. I've quickly read a few recommendations by NSA, NIST, & other fellows, which talk about 2030 & beyond. That's what I'm looking for. :)

I'm a bit lost. You both write that the minimum size of the ciphertext would be m + 2*k + 1 + k (m being the size of the message, k being the symmetric key size). I don't really understand where the +1 comes from. :-S

Also, could I just drop the MAC ? Its purpose is to check the message integrity, right ?

Well, is there any "ECIES for the dummies" paper available online ? I must have seen dozens of PDF files describing different versions of ECIES, each with its own names for each figure. :-S

Well thanks again for your help. I hope these few lines describe what I'm doing in a better way. :)

--
John Doe
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