From e98aae3d2c561913d0189064f85236b6adfe871f Mon Sep 17 00:00:00 2001
From: silverpill <silverpill@firemail.cc>
Date: Mon, 14 Nov 2022 00:12:40 +0000
Subject: [PATCH] Add FEP-c390: Identity Proofs

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+---
+authors: silverpill <silverpill@firemail.cc>
+status: DRAFT
+dateReceived: 2022-11-23
+---
+# FEP-c390: Identity Proofs
+
+## Summary
+
+This proposal describes a mechanism of linking cryptographic keys to [ActivityPub](https://www.w3.org/TR/activitypub/) actor profiles.
+
+## History
+
+- Mastodon implemented [identity proofs](https://github.com/mastodon/mastodon/pull/10414) in 2019. Keybase platform was used as an identity provider, but the integration was later [removed](https://github.com/mastodon/mastodon/pull/17045).
+- [Keyoxide](https://keyoxide.org/) can create off-protocol identity proofs for Fediverse profiles [using OpenPGP](https://docs.keyoxide.org/service-providers/activitypub/).
+
+## Identity proofs
+
+Identity proof is a JSON document that represents a verifiable bi-directional link between a [Decentralized Identifier](https://www.w3.org/TR/did-core/) and an ActivityPub actor.
+
+It MUST contain the following properties:
+
+- `type` (REQUIRED): the `type` property MUST contain the string `Identity`.
+- `id` (REQUIRED): the decentralized identifier (DID) that represents a cryptographic key belonging to an actor.
+- `alsoKnownAs` (REQUIRED): the value of this property MUST match the actor ID.
+- `proof` (REQUIRED): the data integrity proof, as defined by [Data Integrity](https://w3c.github.io/vc-data-integrity/) specification.
+
+The document MUST not contain any additional properties.
+
+Identity proofs SHOULD be attached to an actor object, under the `attachment` property.
+
+### Proof generation
+
+The identity proof document MUST contain a data integrity proof, which includes a cryptographic proof and parameters required to verify it. It MUST be created according to the *Data Integrity* specification, section [4.1 Generate Proof](https://w3c.github.io/vc-data-integrity/#generate-proof). The value of `verificationMethod` property of the data integrity proof MUST match the value of `id` property of the identity proof document.
+
+The resulting data integrity proof MUST be added to identity proof document under the `proof` key.
+
+Example:
+
+```json
+{
+    "@context": "https://www.w3.org/ns/activitystreams",
+    "type": "Person",
+    "id": "https://example.com/users/alice",
+    "inbox": "https://example.com/users/alice/inbox",
+    "attachment": [
+        {
+            "type": "Identity",
+            "id": "did:key:z6MkhaXgBZDvotDkL5257faiztiGiC2QtKLGpbnnEGta2doK",
+            "alsoKnownAs": "https://example.com/users/alice",
+            "proof": {
+                "type": "JcsEd25519Signature2022",
+                "created": "2022-11-12T00:00:00Z",
+                "verificationMethod": "did:key:z6MkhaXgBZDvotDkL5257faiztiGiC2QtKLGpbnnEGta2doK",
+                "proofPurpose": "assertionMethod",
+                "proofValue": "<proof-value>"
+            }
+        }
+    ]
+}
+```
+
+### Proof verification
+
+The receiving server MUST check the authenticity of identity proof document by verifying its data integrity proof. If the server can't verify the proof, or if the value of `verificationMethod` property of the data integrity proof doesn't match the value of `id` property of the identity proof, or if the value of `alsoKnownAs` property of the identity proof doesn't match the actor ID, the identity proof MUST be discarded.
+
+Verification process MUST follow the *Data Integrity* specification, section [4.2 Verify Proof](https://w3c.github.io/vc-data-integrity/#verify-proof).
+
+The receiving server SHOULD treat identities denoted by `id` and `alsoKnownAs` properties of identity proof as belonging to the same entity.
+
+## References
+
+- [ActivityPub] Christine Lemmer Webber, Jessica Tallon, [ActivityPub](https://www.w3.org/TR/activitypub/), 2018
+- [Decentralized Identifier] Manu Sporny, Dave Longley, Markus Sabadell, Drummond Reed, Orie Steele, Christopher Allen, [Decentralized Identifiers (DIDs) v1.0](https://www.w3.org/TR/did-core/), 2022
+- [Data Integrity] Dave Longley, Manu Sporny, [Verifiable Credential Data Integrity 1.0](https://w3c.github.io/vc-data-integrity/), 2022
+
+## Copyright
+
+CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
+
+To the extent possible under law, the authors of this Fediverse Enhancement Proposal have waived all copyright and related or neighboring rights to this work.