RE: json-ld signatures with Ed25519VerificationKey2018

> See: https://tools.ietf.org/html/rfc7797#page-7
This is exactly what I was looking for 😊 Thanks!

In any case, we are trying to understand how JSON-LD Ed25519Signature2018 Signatures are generated. As an exercise we wrote a small python script that uses PyLD and pynacl to output the proof part of a document. The output it generates is the same as digital bazaar's library so I guess it is correct. I leave the link here in case anybody wants to check it *for educational purposes*

https://github.com/mmlab-aueb/PyEd25519Signature2018

Best,
Nikos

-----Original Message-----
From: Dave Longley <dlongley@digitalbazaar.com> 
Sent: Wednesday, June 3, 2020 5:10 PM
To: Nikos Fotiou <fotiou@aueb.gr>; public-credentials@w3.org
Subject: Re: json-ld signatures with Ed25519VerificationKey2018

On 6/2/20 10:23 PM, Nikos Fotiou wrote:
> Hi all,
> I am experimenting with json-ld signatures, using digital bazaar's 
> library https://github.com/digitalbazaar/jsonld-signatures
> 
> I notice when this algorithm is used Ed25519VerificationKey2018 the 
> library crates a jwt with the following header:
> header = {
>     "alg": "EdDSA",
>     "b64": False,
>     "crit": ["b64"]
> }
> I am struggling to understand what is this header and why is there. Anybody?

The signature value for Ed25519Signature2018 is a detached JWS on an unencoded payload (no base64 encoding applied). Since the value is a JWS, this includes a header -- and since it is an EdDSA signature over an unencoded payload, the above parameters are expressed.

See: https://tools.ietf.org/html/rfc7797#page-7

An effort was made with the Ed25519Signature2018 and RsaSignature2018 signature suites to get more alignment with JWS -- and expressing the signature value as a JWS in this manner is the outcome of that.


--
Dave Longley
CTO
Digital Bazaar, Inc.