Reworked w3c credentials and presentations to use DataIntegrityProof instead of custom AnonCreds context

[Artemkaaas]

Update W3C Credential to match the design: hyperledger/anoncreds-spec#192

I also included changes from the following PRs as their changes significantly intersected with the current one:

• Drop encoding - AnonCreds Credentials using the W3C Standard - drop encoding from credential schema #284
• Drop mapping - AnonCreds Credentials using the W3C Standard - drop mapping from presentation #274

Regarding vc format 1.1/2.0: I added an option parameter version to anoncreds_process_w3c_credential, anoncreds_credential_to_w3c, and anoncreds_create_w3c_presentation functions defining what vc format to return.

[TimoGlastra]

I tried to go over it, but there's a lot of changed code, so it's a bit hard to look really in-depth whether are changes are correct. But overall looks good to me!

[TimoGlastra]

@swcurran my suggestion would still be to add some more dashes, and make pres -> proof. Proof is what also seems to have been used in bbs suite.

So anoncreds-vc-2023 and anoncreds-vc-proof-2023. Or maybe something like ac-vc-23 and ac-vc-proof-23 (or cl-vc-23)

[TimoGlastra]

I think one thing that is missing to make it compliant with the DI spec is that the proofValue MUST be multibase encoded and have a header:

A string value that contains the base-encoded binary data necessary to verify the digital proof using the verificationMethod specified. The contents of the value MUST be expressed with a header and encoding as described in Section 2.4 Multibase. The contents of this value are determined by a specific cryptosuite and set to the proof value generated by the Add Proof Algorithm for that cryptosuite. Alternative properties with different encodings specified by the cryptosuite MAY be used, instead of this property, to encode the data necessary to verify the digital proof.

I don't know if there's a multibase format we can use that won't add too much overhead to the final proofValue? It must decode to the binary data needed to verify the proof. I don't know if the output of messagepack is binary? If so, we could do a base64 pass on it and use that as the proofValue?

Here's a list of all multibase types: https://github.com/multiformats/multibase/blob/master/multibase.csv

[Artemkaaas]

@TimoGlastra I already applied multibase encoding for the proof value with u prefix (base64 no padding) here:

https://github.com/hyperledger/anoncreds-rs/pull/291/files#diff-0423f5bfbbb105eb8c19ba64df62479a284b630ed112415e211756ac7b2d38d1

const BASE_HEADER: char = 'u';

pub trait EncodedObject {
    fn encode(&self) -> String
    where
        Self: Serialize,
    {
        let json = json!(self).to_string();
        let serialized = base64::encode(json);
        format!("{}{}", BASE_HEADER, serialized)
    }

    fn decode(string: &str) -> Result<Self>
    where
        Self: DeserializeOwned,
    {
        match string.chars().next() {
            Some(BASE_HEADER) => {
                // ok
            }
            value => return Err(err_msg!("Unexpected multibase base header {:?}", value)),
        }
        let decoded = base64::decode(&string[1..])?;
        let obj: Self = serde_json::from_slice(&decoded)?;
        Ok(obj)
    }
}

[TimoGlastra]

Oh woops, sorry completely missed that.

Nice 😬

[swcurran]

@Artemkaaas — there is a conflict in the PR now. Could you please resolve and we’ll merge this. Sorry for the delay over the break.