# Credential Exchange

> Stephen Curran - based on the Indy Agent WG call from 2019.03.20, I propose that we use the following messages for the 0.1 Version of the Credential Exchange Protocol. This is to make some things work for IIW. The in-process HIPE will be the ongoing HIPE that will be (eventually accepted).
>
> Update - 2019.03.28 - We are not going to be using the `proposal` messages for our IIW demo, and so have indicated they are off the table in this document. We look forward to adding them post-IIW.
>

## Issue Credential Protocol

The process can begin with either a `credential-offer` or a `credential-proposal` message. In some cases - and specifically, the case of Indy Catalyst Credential Registry (aka OrgBook), many credentials can be issued (via `credential-issue` messages) based on the same `credential-request`.

The thread decorator is implied for all messages except the first.

The <libindy json string> element is used in most messages and is the string returned from libindy for the given purpose - an escaped JSON string. The agent must process the string if there is a need to extract a data element from the JSON - for example to get the `cred-def-id` from the `credential-offer`.

Acknowledgments and Errors should be signalled via adopting the standard `ack` and `problem-report` message types, respectively.

---

### Credential Offer

The `credential_preview` attribute is optional.

{
    "@type": "did:sov:BzCbsNYhMrjHiqZDTUASHg;spec/credential-issuance/0.1/credential-offer",
    "@id": "<uuid-offer>",
    "comment": "some comment",
    "credential_preview": <json-ld object>,
    "offer_json": <libindy json string>
}

The `credential_preview` JSON-LD object will be:

{
    "@type": "did:sov:BzCbsNYhMrjHiqZDTUASHg;spec/credential-issuance/0.1/credential-preview",
    "@context": string,
    "@id": string,
    "attributes": [
        {
            "name": "attribute name",
            "mime-type": "type",
            "value": "value"
        },
        ...
    ]
}

### ~~Credential Proposal~~

~~This is a message from the Prover to the Issuer indicating the credential data wanted. This message can be sent in response to a credit offer or to initiate a request.~~

~~**IDEA**: If the message is sent to initiate a request, the data in the comment or credential preview (*which one makes sense? either?*) could be used as input parameters for a search to get the data for a credential.~~

> ~~Use Case: When requesting a "verified email address" credential, the proposal is used to send to the issuer the email address to be verified.~~

~~The `credential_preview` attribute is optional~~

{
    "@type": "did:sov:BzCbsNYhMrjHiqZDTUASHg;spec/credential-issuance/0.1/credential-proposal",
    "@id": "<uuid-offer>",
    "comment": "some comment",
    "credential_preview": "<json-ld object>",
    "proposal" : {
        "cred_def_id": string,
        "schema_id": string
    }
}

~~Either a cred_def_id or a schema_id can be included, but there should not be both.~~

### Credential Request

{
    "@type": "did:sov:BzCbsNYhMrjHiqZDTUASHg;spec/credential-issuance/0.1/credential-request",
    "@id": "<uuid-request>",
    "comment": "some comment",
    "request": <libindy json string>
}

### Credential Issue

{
    "@type": "did:sov:BzCbsNYhMrjHiqZDTUASHg;spec/credential-issuance/0.1/credential-issue",
    "@id": "<uuid-credential>",
    "issue": <libindy json string>
}

---

## Presentation Protocol

> Switch terminology now to use "Presentation" instead of "Proof" to align with W3C.

The message family to initiate a presentation. Either party (prover or verifier) can initiate the process.

The thread decorator is implied on every message other than the first message.

The `ack` and `problem-report` messages are to be adopted by this message family.

### Presentation Request

{
    "@type": "did:sov:BzCbsNYhMrjHiqZDTUASHg;spec/credential-presentation/0.1/presentation-request",
    "@id": "<uuid-request>",
    "comment": "some comment",
    "request": <libindy json string>
}

### ~~Presentation Proposal~~

~~Negotiation message from the Prover to the Verifier. This could be used to initiate a presentation or to provide a counter offer to a presentation request.~~

{
    "@type": "did:sov:BzCbsNYhMrjHiqZDTUASHg;spec/credential-presentation/0.1/presentation-proposal",
    "@id": "<uuid-request>",
    "comment": "some comment",
    "proposalemail ": <libindy json string>
}

### Credential-Presentation

{
    "@type": "did:sov:BzCbsNYhMrjHiqZDTUASHg;spec/credential-presentation/0.1/credential-presentation",
    "@id": "<uuid-presentation>",
    "comment": "some comment",
    "presentation": <libindy json string>
}