Re: Ed25519 Signature 2018

(adding Credentials CG alias)

Hi Vaneev,
I'll kick off the discussion by answering the parts I know

> 1) How can I create my modification of Ed25519Signature2018 to support
sha3-512 digestAlgorithm?

I believe this would need to be a new signature suite; the general pattern
is to have each suite specify a safe combination of
canonicalization/digest/signature algorithms rather than have options
within a given suite.

See section 6 "Signature Suites" of the LD Signatures spec
https://w3c-dvcg.github.io/ld-signatures/

This community can likely help you get started if that path makes sense.

> 2) I am aware how digital signatures work and I can’t really understand
what should be signed, if data is represented as json-ld. What algorithm is
used to represent json-ld document as bytes before signing?

RDF dataset normalization (canonicalization) described here (
http://json-ld.github.io/normalization/spec/) allows a deterministic
representation before signing and verifying (with the "signature" section
removed in the latter case).

Each signature suite specifies its precise canonicalization algorithm but I
realize that I don't have references as to the differences (this would be
useful). Some examples you'll see in the suites and code are URGNA2012,
URDNA2015, GCA2015.

In any case, you'll likely be able to reuse an existing LD
signature/verification library that will take care of those details for you.

There are several reference implementations and tools you can use to get
started, e.g.:
- https://github.com/digitalbazaar/jsonld.js
- https://json-ld.org/playground/

And many more; let us know if you're looking for specific language support.

This is emphasizing that we need a good cleanup of our docs (indexing,
updating links, etC). We have a couple of github issuances tracking this,
but for now let us know if you need pointers.

Thanks,
Kim

On Sun, May 6, 2018 at 11:49 AM Vaneev Bogdan <bogdan@soramitsu.co.jp>
wrote:

> Hello.
>
> I am following https://w3c-dvcg.github.io/lds-ed25519-2018/ and I see
> that current cipher suite uses sha512, which is from sha2 family.
>
> I want to use Ed25519 implementation with SHA3-512, because it is used in
> https://github.com/hyperledger/iroha and I don’t really know how to
> modify Ed25519Signature2018
>
> And, in general, I don’t understand few things and I would be very
> thankful, if you point me to related materials and answer these questions:
>
> 1) How can I create my modification of Ed25519Signature2018 to support
> sha3-512 digestAlgorithm?
>
> 2) I am aware how digital signatures work and I can’t really understand
> what should be signed, if data is represented as json-ld. What algorithm is
> used to represent json-ld document as bytes before signing?
>
> 3) This is used to https://w3id.org/security#Ed25519Signature2018
> Refer to parameters, used in Ed25519Signature2018, but this link is broken
> (there is no Ed25519Signature2018). It was deleted?
>
>
> Thank you for your time.
>
> Bogdan,
> Soramitsu Software Engineer.
>
-- 
Kim Hamilton Duffy
CTO & Principal Architect Learning Machine
Co-chair W3C Credentials Community Group
400 Main Street Building E19-732, Cambridge, MA 02139

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