Activity Anchors v0.1

Activity Anchors are based on a federated and replicated Verifiable Data Registry (VDR). The decentralized network consists of Activity Anchor Servers that write, monitor, witness, and propagate batches of document operations. The batches form a graph that is propagated and replicated between the servers as content-addressable objects. These content-addressable objects can be located via both domain and distributed hash table (DHT) mechanisms. Each Activity Anchor witness server observes a subset of batches in the graph and includes them in their ledgers (as append-only Merkle Tree logs). The servers coordinate by propagating batches of document operations and by monitoring the applicable witness servers' ledgers. The Activity Anchor servers form a decentralized network without reliance on a common blockchain for coordination.

This document specifies a data model and rules for representing a graph of batches, the anchor server API, an [[[ACTIVITYSTREAMS-CORE]]] vocabulary and an [[[ACTIVITYPUB]]] profile for propagating batches, and a [[[RFC7033]]] profile for discovering endpoints.

Server-to-Server APIs

An Activity Anchor Server exposes APIs for propagation, content-addressable storage, discovery, and witnessing.

Vocabulary

AnchorEvent

An operation batch is represented as an AnchorEvent. Hashlinks [[HASHLINK]] are used to link objects to the AnchorEvent.

Hashlinks may refer to the contentObject within an AnchorObject. Prior to creating the hash in the Hashlink, the contents of the contentObject MUST be canoncialized using the JSON Canonicalization Scheme (JCS) [[RFC8785]]. The Hashlink refers to the canonicalized contents of the contentObject.

              {
                "@context": "https://w3id.org/activityanchors/v1",
                "object": {
                  "linkset": [
                    {
                      "anchor": "hl:uEiB9Chtelm2NlC00j8_I0Febv5Lre3Qsp-ElzpYPeO2HhA",
                      "author": "https://orb.domain2.com/services/orb",
                      "original": [
                        {
                          "href": "data:application/json,%7B%22linkset%22%3A%5B%7B%22anchor%22%3A%22hl%3AuEiBEYPquNVjC7fIduIkd7za-va4KJ5_g6DlQCpBhb8G58w%22%2C%22author%22%3A%22https%3A%2F%2Forb.domain2.com%2Fservices%2Forb%22%2C%22item%22%3A%5B%7B%22href%22%3A%22did%3Aorb%3AuEiBvtB4n61hbCWzfbquORj6OD_j4OD4nCSXs4oVuVNuucA%3AEiBlWWTU5i71R2uOAq04RZlNC148RN44gRAzSU9t4_hVGg%22%2C%22previous%22%3A%22hl%3AuEiBvtB4n61hbCWzfbquORj6OD_j4OD4nCSXs4oVuVNuucA%22%7D%2C%7B%22href%22%3A%22did%3Aorb%3AuEiAGmhR9leewo8DEVhzh5dL6XjwCjqO9H_nGXdBhPf8WlA%3AEiAPvYn4qoOwAQLjtBqur563OgicWQaH4lB1RMh9oEER0Q%22%2C%22previous%22%3A%22hl%3AuEiAGmhR9leewo8DEVhzh5dL6XjwCjqO9H_nGXdBhPf8WlA%22%7D%2C%7B%22href%22%3A%22did%3Aorb%3AuEiAGmhR9leewo8DEVhzh5dL6XjwCjqO9H_nGXdBhPf8WlA%3AEiCQGgEaHyhghhRIsT4hav8GMwRl-EuyGP_DMULTNTfZUg%22%2C%22previous%22%3A%22hl%3AuEiAGmhR9leewo8DEVhzh5dL6XjwCjqO9H_nGXdBhPf8WlA%22%7D%2C%7B%22href%22%3A%22did%3Aorb%3AuEiAGmhR9leewo8DEVhzh5dL6XjwCjqO9H_nGXdBhPf8WlA%3AEiA4SRtKtlBGm-VS78mtZEiAOBysN_ra8zv66Gnw_uJw4A%22%2C%22previous%22%3A%22hl%3AuEiAGmhR9leewo8DEVhzh5dL6XjwCjqO9H_nGXdBhPf8WlA%22%7D%5D%2C%22profile%22%3A%22https%3A%2F%2Fw3id.org%2Forb%23v0%22%7D%5D%7D",
                          "type": "application/linkset+json"
                        }
                      ],
                      "profile": "https://w3id.org/orb#v0",
                      "related": [
                        {
                          "href": "data:application/json,%7B%22linkset%22%3A%5B%7B%22anchor%22%3A%22hl%3AuEiB9Chtelm2NlC00j8_I0Febv5Lre3Qsp-ElzpYPeO2HhA%22%2C%22profile%22%3A%22https%3A%2F%2Fw3id.org%2Forb%23v0%22%2C%22up%22%3A%5B%7B%22href%22%3A%22hl%3AuEiBvtB4n61hbCWzfbquORj6OD_j4OD4nCSXs4oVuVNuucA%3AuoQ-BeEJpcGZzOi8vYmFma3JlaWRwd3FwY3AyMnlsbWV3engzb3ZvaGVtcHVvYjc0cHFvYjZlNGVzbDNoY3F2eGZqdzVvb2E%22%7D%2C%7B%22href%22%3A%22hl%3AuEiAGmhR9leewo8DEVhzh5dL6XjwCjqO9H_nGXdBhPf8WlA%3AuoQ-BeEJpcGZzOi8vYmFma3JlaWFndGlraDNmcGh3Y3I0YnJjd2R0cTZsdXgybHk2YWZkdmR4dXA3dHJzNTJicXQzN3l3c3E%22%7D%5D%2C%22via%22%3A%5B%7B%22href%22%3A%22hl%3AuEiBEYPquNVjC7fIduIkd7za-va4KJ5_g6DlQCpBhb8G58w%3AuoQ-BeEJpcGZzOi8vYmFma3JlaWNlbWQ1azRua3l5bHc3ZWhueXJlbzY2bnY2eHd4YXVqNDc0ZHVkc3Vha3NicXc3cW56Nm0%22%7D%5D%7D%5D%7D",
                          "type": "application/linkset+json"
                        }
                      ],
                      "replies": [
                        {
                          "href": "data:application/json,%7B%22%40context%22%3A%5B%22https%3A%2F%2Fwww.w3.org%2F2018%2Fcredentials%2Fv1%22%2C%22https%3A%2F%2Fw3id.org%2Fsecurity%2Fsuites%2Fed25519-2020%2Fv1%22%5D%2C%22credentialSubject%22%3A%22hl%3AuEiB9Chtelm2NlC00j8_I0Febv5Lre3Qsp-ElzpYPeO2HhA%22%2C%22id%22%3A%22https%3A%2F%2Forb.domain2.com%2Fvc%2F36c995be-99bb-4d0b-9a47-7027aee67bfe%22%2C%22issuanceDate%22%3A%222022-03-17T19%3A50%3A48.7559537Z%22%2C%22issuer%22%3A%22https%3A%2F%2Forb.domain2.com%22%2C%22proof%22%3A%5B%7B%22created%22%3A%222022-03-17T19%3A50%3A48.7567186Z%22%2C%22domain%22%3A%22https%3A%2F%2Forb.domain2.com%22%2C%22proofPurpose%22%3A%22assertionMethod%22%2C%22proofValue%22%3A%22_nOavU_Te7QCyj6GIxGtnER-SWvawrUygcqt-3HyV_3P_LahVxxZmuNtOdPtrRTI4aZJUM6NmUMq_7gxX5ZFDw%22%2C%22type%22%3A%22Ed25519Signature2020%22%2C%22verificationMethod%22%3A%22did%3Aweb%3Aorb.domain2.com%23orb2key%22%7D%2C%7B%22created%22%3A%222022-03-17T19%3A50%3A49.245Z%22%2C%22domain%22%3A%22http%3A%2F%2Forb.vct%3A8077%2Fmaple2020%22%2C%22proofPurpose%22%3A%22assertionMethod%22%2C%22proofValue%22%3A%22bzvRXEWAcskOjz6WgUDDos3e9SiS2DfwmRAwHeuO3rBc0vmbSF6DiVyqeNUc_cSQ8OBYasSiTnWZaJmaEHRVBw%22%2C%22type%22%3A%22Ed25519Signature2020%22%2C%22verificationMethod%22%3A%22did%3Aweb%3Aorb.domain1.com%23orb1key2%22%7D%5D%2C%22type%22%3A%22VerifiableCredential%22%7D",
                          "type": "application/ld+json"
                        }
                      ]
                    }
                  ]
                },
                "type": "AnchorEvent",
                "url": "hl:uEiA-eY77-FHYKR5EyMZc3JIwJIowz3dl91oY-14Wxi3STg:uoQ-BeEJpcGZzOi8vYmFma3JlaWI2cGdocHg2Y3IzYXVyNHJnaXl6b256ZXJxZXNmZGJ0M3hteDN2dWdoM2x5bG1tbG9zank"                
              }

              hl:uEiAsiwjaXOYDmOHxmvDl3Mx0TfJ0uCar5YXqumjFJUNIBg:uoQ-CeEdodHRwczovL2V4YW1wbGUuY29tL2Nhcy91RWlBc2l3amFYT1lEbU9IeG12RGwzTXgwVGZKMHVDYXI1WVhxdW1qRkpVTklCZ3hCaXBmczovL2JhZmtyZWlibXJtZW51eGhnYW9tb2Q0bTI2ZHM1enRkdWp4emhqb2JndnBzeWwydjJuZGNza3EyaWF5",

The example hashlink includes links to `https://example.com/cas/uEiAsiwjaXOYDmOHxmvDl3Mx0TfJ0uCar5YXqumjFJUNIBg` and `ipfs://bafkreibmrmenuxhgaomod4m26ds5ztdujxzhjobgvpsyl2v2ndcskq2iay` to demonstrate that multiple sources and protocols can be used for each object.

TODO: Complete the description of anchor events.

Witnessed Event

A witnessed operation batch is represented as a VerifiableCredential. The credentialSubject contains the hash of the witnessed object. The Verifiable Credential is referenced in the AnchorEvent replies property.

              {
                "@context": [
                  "https://www.w3.org/2018/credentials/v1",
                  "https://w3id.org/security/suites/ed25519-2020/v1"
                ],
                "credentialSubject": "hl:uEiB9Chtelm2NlC00j8_I0Febv5Lre3Qsp-ElzpYPeO2HhA",
                "id": "https://orb.domain2.com/vc/36c995be-99bb-4d0b-9a47-7027aee67bfe",
                "issuanceDate": "2022-03-17T19:50:48.7559537Z",
                "issuer": "https://orb.domain2.com",
                "proof": [
                  {
                    "created": "2022-03-17T19:50:48.7567186Z",
                    "domain": "https://orb.domain2.com",
                    "proofPurpose": "assertionMethod",
                    "proofValue": "_nOavU_Te7QCyj6GIxGtnER-SWvawrUygcqt-3HyV_3P_LahVxxZmuNtOdPtrRTI4aZJUM6NmUMq_7gxX5ZFDw",
                    "type": "Ed25519Signature2020",
                    "verificationMethod": "did:web:orb.domain2.com#orb2key"
                  },
                  {
                    "created": "2022-03-17T19:50:49.245Z",
                    "domain": "http://orb.vct:8077/maple2020",
                    "proofPurpose": "assertionMethod",
                    "proofValue": "bzvRXEWAcskOjz6WgUDDos3e9SiS2DfwmRAwHeuO3rBc0vmbSF6DiVyqeNUc_cSQ8OBYasSiTnWZaJmaEHRVBw",
                    "type": "Ed25519Signature2020",
                    "verificationMethod": "did:web:orb.domain1.com#orb1key2"
                  }
                ],
                "type": "VerifiableCredential"
              }

ActivityPub

This section defines a minimal profile of [[ACTIVITYPUB]] that Activity Anchor Servers implement to participate in propagation flows.

Actor (Discovery)

An Actor exposed by an Activity Anchor Server is capable of participating in propagation flows. ActivityPub endpoints are retrieved by performing an HTTP GET to the Actor endpoint. The Actor endpoint returns an Actor object.

              GET /services/anchor HTTP/1.1
              Host: alice.example.com
              Accept: application/ld+json; profile="https://www.w3.org/ns/activitystreams"
              Accept-Encoding: gzip, deflate

When the service profile exists, an HTTP 200 status code is returned.

              HTTP/1.1 200 OK
              Date: Wed, 27 Jan 2021 21:57:25 GMT
              Content-Type: application/jrd+json; charset=utf-8
              Connection: keep-alive
              Access-Control-Allow-Origin: *

              {
                "@context": [
                "https://www.w3.org/ns/activitystreams",
                "https://w3id.org/security/v1",
                "https://w3id.org/activityanchors/v1"
                ],
                "id": "https://alice.example.com/services/anchor",
                "type": "Service",
                "publicKey": {
                  "id": "https://alice.example.com/services/anchor#main-key",
                  "owner": "https://alice.example.com/services/anchor",
                  "publicKeyPem": "-----BEGIN PUBLIC KEY-----\nMIIBIjANBgkqhki....."
                },
                "inbox": "https://alice.example.com/services/anchor/inbox",
                "outbox": "https://alice.example.com/services/anchor/outbox",
                "followers": "https://alice.example.com/services/anchor/followers",
                "following": "https://alice.example.com/services/anchor/following",
                "witnesses": "https://alice.example.com/services/anchor/witnesses",
                "witnessing": "https://alice.example.com/services/anchor/witnessing",
                "likes": "https://alice.example.com/services/anchor/likes",
                "liked": "https://alice.example.com/services/anchor/liked",
                "shares": "https://alice.example.com/services/anchor/shares"
              }

TODO: Review handling of publicKey.

Delivery

Activity Anchor Servers use ActivityPub Delivery mechanisms to propagate anchor activitys and to request to follow other servers. A propagation or follow request is sent by performing an HTTP POST of an activity to an Activity Anchor Server's ActivityPub inbox endpoint.

Activity Anchor Servers use HTTP Signatures [[HTTP-SIGNATURES]] when calling Server-to-Server APIs to create authenticated messages. The anchor objects are additionally signed using JSON-LD proofs [[LDPROOF]] from both the Writer server as well as Witness servers.

Collections

Please refer to [[ACTIVITYPUB]] section 5 for general collections guidance. An Activity Anchor Server exposes:

Outbox: provides an ordered collection of the activities published by the server.
Inbox: provides an ordered collection of the activities received by the server.
Followers: provides a collection (or ordered collection) of the other Activity Anchor Servers following the server.
Following: provides a collection (or ordered collection) of the other Activity Anchor Servers the server is following.
Witnesses: provides a collection (or ordered collection) of the other Activity Anchor Servers that act as witnesses.
Witnessing: provides a collection (or ordered collection) of the other Activity Anchor Servers the server is witnessing.
Likes: provides an ordered collection of the processed and replicated anchor activities sent by an Activity Anchor Server.
Liked: provides an ordered collection of the anchor activities processed and replicated by the Activity Anchor Server.
Shares: provides an ordered collection of the propagation (announce) activities sent by the Activity Anchor Server.

Create Activity

An Activity Anchor Server that creates a anchor activity uses an Create activity to propagate that knowledge to its own followers. A anchor activity is propagated to another Activity Anchor Server by performing an HTTP POST of an Create activity containing an AnchorCredential to its ActivityPub inbox endpoint.

              POST /services/anchor/inbox HTTP/1.1
              Host: alice.example.com
              Content-Type: application/ld+json; profile="https://www.w3.org/ns/activitystreams"
              Accept-Encoding: gzip, deflate

              {
                "@context": "https://www.w3.org/ns/activitystreams",
                "actor": "https://orb.domain2.com/services/orb",
                "id": "https://orb.domain2.com/services/orb/activities/33762e97-3826-4b24-86ac-91356ca75299",
                "object": {
                  "@context": "https://w3id.org/activityanchors/v1",
                  "object": {
                    "linkset": [
                      {
                        "anchor": "hl:uEiB9Chtelm2NlC00j8_I0Febv5Lre3Qsp-ElzpYPeO2HhA",
                        "author": "https://orb.domain2.com/services/orb",
                        "original": [
                          {
                            "href": "data:application/json,%7B%22linkset%22%3A%5B%7B%22anchor%22%3A%22hl%3AuEiBEYPquNVjC7fIduIkd7za-va4KJ5_g6DlQCpBhb8G58w%22%2C%22author%22%3A%22https%3A%2F%2Forb.domain2.com%2Fservices%2Forb%22%2C%22item%22%3A%5B%7B%22href%22%3A%22did%3Aorb%3AuEiBvtB4n61hbCWzfbquORj6OD_j4OD4nCSXs4oVuVNuucA%3AEiBlWWTU5i71R2uOAq04RZlNC148RN44gRAzSU9t4_hVGg%22%2C%22previous%22%3A%22hl%3AuEiBvtB4n61hbCWzfbquORj6OD_j4OD4nCSXs4oVuVNuucA%22%7D%2C%7B%22href%22%3A%22did%3Aorb%3AuEiAGmhR9leewo8DEVhzh5dL6XjwCjqO9H_nGXdBhPf8WlA%3AEiAPvYn4qoOwAQLjtBqur563OgicWQaH4lB1RMh9oEER0Q%22%2C%22previous%22%3A%22hl%3AuEiAGmhR9leewo8DEVhzh5dL6XjwCjqO9H_nGXdBhPf8WlA%22%7D%2C%7B%22href%22%3A%22did%3Aorb%3AuEiAGmhR9leewo8DEVhzh5dL6XjwCjqO9H_nGXdBhPf8WlA%3AEiCQGgEaHyhghhRIsT4hav8GMwRl-EuyGP_DMULTNTfZUg%22%2C%22previous%22%3A%22hl%3AuEiAGmhR9leewo8DEVhzh5dL6XjwCjqO9H_nGXdBhPf8WlA%22%7D%2C%7B%22href%22%3A%22did%3Aorb%3AuEiAGmhR9leewo8DEVhzh5dL6XjwCjqO9H_nGXdBhPf8WlA%3AEiA4SRtKtlBGm-VS78mtZEiAOBysN_ra8zv66Gnw_uJw4A%22%2C%22previous%22%3A%22hl%3AuEiAGmhR9leewo8DEVhzh5dL6XjwCjqO9H_nGXdBhPf8WlA%22%7D%5D%2C%22profile%22%3A%22https%3A%2F%2Fw3id.org%2Forb%23v0%22%7D%5D%7D",
                            "type": "application/linkset+json"
                          }
                        ],
                        "profile": "https://w3id.org/orb#v0",
                        "related": [
                          {
                            "href": "data:application/json,%7B%22linkset%22%3A%5B%7B%22anchor%22%3A%22hl%3AuEiB9Chtelm2NlC00j8_I0Febv5Lre3Qsp-ElzpYPeO2HhA%22%2C%22profile%22%3A%22https%3A%2F%2Fw3id.org%2Forb%23v0%22%2C%22up%22%3A%5B%7B%22href%22%3A%22hl%3AuEiBvtB4n61hbCWzfbquORj6OD_j4OD4nCSXs4oVuVNuucA%3AuoQ-BeEJpcGZzOi8vYmFma3JlaWRwd3FwY3AyMnlsbWV3engzb3ZvaGVtcHVvYjc0cHFvYjZlNGVzbDNoY3F2eGZqdzVvb2E%22%7D%2C%7B%22href%22%3A%22hl%3AuEiAGmhR9leewo8DEVhzh5dL6XjwCjqO9H_nGXdBhPf8WlA%3AuoQ-BeEJpcGZzOi8vYmFma3JlaWFndGlraDNmcGh3Y3I0YnJjd2R0cTZsdXgybHk2YWZkdmR4dXA3dHJzNTJicXQzN3l3c3E%22%7D%5D%2C%22via%22%3A%5B%7B%22href%22%3A%22hl%3AuEiBEYPquNVjC7fIduIkd7za-va4KJ5_g6DlQCpBhb8G58w%3AuoQ-BeEJpcGZzOi8vYmFma3JlaWNlbWQ1azRua3l5bHc3ZWhueXJlbzY2bnY2eHd4YXVqNDc0ZHVkc3Vha3NicXc3cW56Nm0%22%7D%5D%7D%5D%7D",
                            "type": "application/linkset+json"
                          }
                        ],
                        "replies": [
                          {
                            "href": "data:application/json,%7B%22%40context%22%3A%5B%22https%3A%2F%2Fwww.w3.org%2F2018%2Fcredentials%2Fv1%22%2C%22https%3A%2F%2Fw3id.org%2Fsecurity%2Fsuites%2Fed25519-2020%2Fv1%22%5D%2C%22credentialSubject%22%3A%22hl%3AuEiB9Chtelm2NlC00j8_I0Febv5Lre3Qsp-ElzpYPeO2HhA%22%2C%22id%22%3A%22https%3A%2F%2Forb.domain2.com%2Fvc%2F36c995be-99bb-4d0b-9a47-7027aee67bfe%22%2C%22issuanceDate%22%3A%222022-03-17T19%3A50%3A48.7559537Z%22%2C%22issuer%22%3A%22https%3A%2F%2Forb.domain2.com%22%2C%22proof%22%3A%5B%7B%22created%22%3A%222022-03-17T19%3A50%3A48.7567186Z%22%2C%22domain%22%3A%22https%3A%2F%2Forb.domain2.com%22%2C%22proofPurpose%22%3A%22assertionMethod%22%2C%22proofValue%22%3A%22_nOavU_Te7QCyj6GIxGtnER-SWvawrUygcqt-3HyV_3P_LahVxxZmuNtOdPtrRTI4aZJUM6NmUMq_7gxX5ZFDw%22%2C%22type%22%3A%22Ed25519Signature2020%22%2C%22verificationMethod%22%3A%22did%3Aweb%3Aorb.domain2.com%23orb2key%22%7D%2C%7B%22created%22%3A%222022-03-17T19%3A50%3A49.245Z%22%2C%22domain%22%3A%22http%3A%2F%2Forb.vct%3A8077%2Fmaple2020%22%2C%22proofPurpose%22%3A%22assertionMethod%22%2C%22proofValue%22%3A%22bzvRXEWAcskOjz6WgUDDos3e9SiS2DfwmRAwHeuO3rBc0vmbSF6DiVyqeNUc_cSQ8OBYasSiTnWZaJmaEHRVBw%22%2C%22type%22%3A%22Ed25519Signature2020%22%2C%22verificationMethod%22%3A%22did%3Aweb%3Aorb.domain1.com%23orb1key2%22%7D%5D%2C%22type%22%3A%22VerifiableCredential%22%7D",
                            "type": "application/ld+json"
                          }
                        ]
                      }
                    ]
                  },
                  "type": "AnchorEvent",
                  "url": "hl:uEiA-eY77-FHYKR5EyMZc3JIwJIowz3dl91oY-14Wxi3STg:uoQ-BeEJpcGZzOi8vYmFma3JlaWI2cGdocHg2Y3IzYXVyNHJnaXl6b256ZXJxZXNmZGJ0M3hteDN2dWdoM2x5bG1tbG9zank"
                },
                "published": "2022-03-17T19:50:51.0429926Z",
                "to": [
                  "https://orb.domain2.com/services/orb/followers",
                  "https://www.w3.org/ns/activitystreams#Public"
                ],
                "type": "Create"
              }