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I want to use the ED25519 signature scheme in my application which requires frequent sharing of secret data between two entities in the public domain.

I know that the Schnorr signature scheme has a key authentication center (KAC) which decides and shares common parameters to be used by signer and verifier. The KAC also signs the public keys of everyone with its own private key. And then the signer signs the message and sends his public key along with the signature to the verifier [From Schnorr's paper 1991].

But is there any KAC in ED25519? And what are the parameters shared in ED25519 by the KAC?

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Ed25519 is well-defined and requires you to use SHA-512 as internal hash function along with the twisted Edwards version of Curve25519, hence there's no need for a KAC when it comes to questions about the parameters. As for the integrity of the public key, there's not yet a standard for Ed25519 based certificates so there would be a custom solution needed for a given application.

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  • $\begingroup$ I'm not sure about which parameters to make public (or send to verifier) and which to be kept secret. There are 7 parameters like b=256, H=SHA-512, q=2^255-19, d=-121665/121666, l=253bit prime and B=(x,4/5). Are all of these shared with verifier? $\endgroup$ – mk09 Apr 13 '16 at 11:46
  • $\begingroup$ @Maheshk, all of these parameter can be considered public and can even be hard-coded for verification if you want to save bandwidth. The only thing you must not send is the private key and any intermediate varibales generated during the signing process. $\endgroup$ – SEJPM♦ Apr 13 '16 at 11:55
  • $\begingroup$ Then hard-coding is the best way for parameters which are constant. Only B should be shared, since its user-defined. $\endgroup$ – mk09 Apr 13 '16 at 12:03
  • $\begingroup$ @Maheshk, B can also be hard-coded since it's a constant (the base point), your public key (a multiple of B) would be user-defined. $\endgroup$ – SEJPM♦ Apr 13 '16 at 12:05
  • $\begingroup$ Waited for the answer for long time and now I got it. Thanks a lot!!! $\endgroup$ – mk09 Apr 13 '16 at 13:57

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