ipip-428: Allowing V2-Only Records in IPNS

initial draft for early feedback

src/ipips/ipip-0428.md

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+---
+title: "IPIP-0428: Allowing V2-Only Records in IPNS"
+date: 2023-07-24
+ipip: proposal
+editors:
+  - name: Marcin Rataj
+    github: lidel
+    url: https://lidel.org/
+    affiliation:
+        name: Protocol Labs
+        url: https://protocol.ai/
+  - name: Henrique Dias
+    github: hacdias
+    url: https://hacdias.com/
+    affiliation:
+        name: Protocol Labs
+        url: https://protocol.ai/
+relatedIssues:
+  - https://github.com/ipfs/specs/issues/376
+order: 428
+tags: ['ipips']
+---
+
+## Summary
+
+Introduce support for creation and validation of compact, V2-only IPNS Records.
+
+## Motivation
+
+IPNS record creation and validation is overly complex due to the legacy of
+decisions made in 2021.
+
+The "V1+V2" record creation and validation was reverse-engineered and documented
+the current state in [ipfs/specs#319](https://github.com/ipfs/specs/pull/319),
+and created a base for specifications to improve upon.
+
+A quick refresher on how IPNS Record lifecycle works today (2023 Q2):
+
+- Record Creation produces both V1 and V2 signatures, and the record has
+  duplicated values in both top level protobuf AND `data` CBOR field.
+
+- Record Validation only cares about V2 signature, but still requires fields
+  related to V1 to be always present in a record and match values from CBOR in
+  `data` field, for the record to be considered valid.
+
+We've been producing and expecting these hybrid V1+V2 records [since 2021](https://github.com/ipfs/js-ipns/pull/121).
+
+An unfortunate result is that all mandatory values MUST be duplicated, even
+when both ends use a modern client that only cares about `signatureV2` that
+guards CBOR field, otherwise the record will not be valid.
+
+What this IPIP aims to improve is allow implementations to produce lean,
+V2-only IPNS records and ensure clients will interpret them as valid IPNS.
+
+## Detailed design
+
+Finish V2 story by making V2-Only records possible, namely:
+
+- creation: document and default to lean V2-Only records, keep V1+V2 as legacy
+  backward-compatible variant
+
+- validation: adjust the algorithm to stop requiring V1 fields when there is no
+  `signatureV1`.
+
+For details, see the updated :cite[ipns-record] specification.
+
+## Design rationale
+
+For modern IPNS, the outer `IpnsEntry` protobuf should effectively only have
+two required fields:  `data` and its `signatureV2`, and such record, as long
+signature is valid, should be accepted as valid.
+
+At the same time, we don't want to break existig software, especially software
+and hardware devices which use IPNS for pulling updates.
+
+We can get to that future in two steps:
+
+1. Reference implementations (go-ipfs, js-ipfs) will keep producing V1+V2
+   records as backward-compatible default, but we adjust validation algorithm
+   to allow V2-only records, and support creation of such records as opt-in.
+   - Namely, only check/require fields to be duplicated in top level protobuf IF
+     `signatureV1` is present in the `IpnsEntry` protobuf.
+     - IF there is no `signatureV1`, the V1 record would be invalid anyway.
+     - IF there is no `signatureV1` but `signatureV2` and `data` fields
+       are present and valid, the V2-only record should be considered valid.
+        - This will allow people to build V2-only systems that produce records that
+          are considered valid.
+
+2. At some point in the future, e.g. when we see the majority of the public
+   swarm supports V2-Only records, libraries like go-ipns/js-ipfs and
+   implementations like Kubo stop producing V1+V2 and switch to publishing
+   V2-only records that are protobuf with only two fields: Data
+   CBOR+signatureV2
+
+
+### User benefit
+
+- End users: the main benefit for end user is smaller size of IPNS record and
+  less complex creation/validation of modern V2-only records.
+
+- Developers interested in IPNS: by making IPNS Record creation as simple as
+  "create DAG-CBOR with these fields, and sign it", and validation to
+  "signatureV2 should match the DAG-CBOR value and key". we've removed surface
+  for bugs, making it easier to reason about for use in greenfield projects.
+
+- IPFS ecosystem: lowering the complexity related to IPNS record creation and
+  validation makes it more likely for third-party interoperable IPNS
+  implementations to happen.
+
+### Compatibility
+
+- This is backward-compatible, we adjust validation logic to allow V2-only
+  records, but all V1+V2 records that are being used in the wild today are
+  still valid
+
+- V2-only rollout is not part of this IPIP.
+  - Our suggestion is to default to creating V1+V2 records for now, keeping
+    backward-compatibility with the old IPNS clients.
+
+  - Creation of V2-only records should be introduced as an explicit opt-in. It
+    is up to implementations to decide when it is feasible to default to
+    creating V2-only records on IPNS publish.
+
+### Security
+
+- `IpnsEntry.signatureV1` (protobuf field) is parsed only by legacy clients, modern ones ignore this value
+
+It is highly advised to implement validation conformance tests using the fixtures
+included at the end of this IPIP.
+
+### Alternatives
+
+Describe alternate designs that were considered and related work.
+
+1. Just switch to V2-only as the new default!
+
+  - No, this would be a breaking change. We have to do this in two steps,
+    because we've rushed the way V2 was introduced in 2021, and STILL require
+    field copying, even when `signatureV1` is missing. So technically there was
+    never "V2", it was more like "V1.5". Only with this IPIP, we finally
+    adjust validation to only care about CBOR values when there is no `signatureV1`.
+
+2. Why keeping the outer protobuf envelope? Could we make IPNS DAG-CBOR-only?
+
+   - Due to how long it takes for decentralized network nodes to upgrade, we prefer evolution rather than revolution.
+   - Protobuf is an useful envelope for two reasons:
+     1. ensures the opaque V2-only record can be passed and stored in existing infrastructure
+     2. allows us to evolve IPNS record ("V3") in the future without impacting existing infrastructure
+
+## Test fixtures
+
+TODO: IPNS record that is valid for 100 years and
+
+1. V1-only → record invalid
+1. V1+V2 (both signatures valid) → record valid
+1. V1+V2 (both signatures valid, but 'value' is different in V1) → record invalid
+1. V1+V2 (only V1 valid) → record invalid
+1. V1+V2 (only V2 valid, V1 missing signature) → record valid (because we do V1 validation only when signatureV1 is present in protobuf)
+1. V2-only (only V2 valid) → record valid
+
+### Copyright
+
+Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).