dip-1: self-describing hash

DIPs/dip-1.md

@@ -0,0 +1,114 @@
+---
+dip: 1
+title: Self-Describing Identifiers for Attestation ReportData
+status: Draft
+author: Hang Yin <[email protected]>
+created: 2025-09-13
+---
+
+## Abstract
+
+This DIP defines `dip1`, a compact self-describing identifier that fits within the 64-byte Intel DCAP `reportdata` field. A fixed scope prefix (`dip1`) is followed by an algorithm label and either a digest or inline payload. The canonical form for hashed payloads is:
+
+```
+dip1:<algo>:<base64url-digest>
+```
+
+The actual payload, which encodes purpose/content-type metadata, is transmitted or embedded separately. An inline variant allows very small payloads to fit entirely inside the identifier.
+
+## Motivation
+
+Attestation workflows need a short, unambiguous identifier for application-defined data that can be carried inside `reportdata`. Without such structure, a verifier that receives a TDX quote can only check the quote envelope itself; it has no portable way to interpret what the embedded `reportdata` is supposed to prove.
+
+By reserving the `dip1` prefix and standardising how algorithms and payload descriptors appear in the identifier, we make `reportdata` self-describing without exceeding the 64-byte budget. A verification platform can inspect the `dip1` string to learn which hash algorithm was used and what content type the payload represents, then route the quote to specialised validation plugins whenever they are available.
+
+## Specification
+
+The general grammar is:
+
+```
+dip1:<algo>:<data>
+```
+
+* `dip1`: Literal ASCII prefix reserving the namespace for this format.
+* `<algo>`: Lowercase token indicating how to interpret `<data>`.
+* `<data>`: Algorithm-dependent ASCII payload.
+
+### Hashed payloads
+
+For cryptographic digests:
+
+```
+dip1:sha256:<base64url-digest>
+```
+
+* `<base64url-digest>` is the URL-safe Base64 (unpadded) encoding of a SHA-256 digest (43 characters).
+* The digest is computed over a canonical payload byte string supplied alongside the attestation evidence. The payload SHOULD begin with its own content-type prefix, e.g. `ratls-pubkey:<hex>`.
+* Other algorithms MAY be supported in the future, but **SHA-256 is normative** for interoperability.
+
+### Inline payloads
+
+Short payloads can be embedded directly using the reserved `inline` algorithm:
+
+```
+dip1:inline:<type>:<base64url-payload>
+```
+
+* `<type>`: Short token (≤8 characters recommended) describing the payload, e.g. `ra-pk`.
+* `<base64url-payload>`: URL-safe Base64 (unpadded) encoding of the raw payload bytes.
+* Inline payloads MUST keep the entire identifier within 64 bytes.
+
+For maximal brevity, the `inline` algorithm MAY be omitted. The double-colon form is an alias for the inline variant:
+
+```
+dip1::<type>:<base64url-payload>
+```
+
+### Size considerations
+
+For the SHA-256 variant:
+
+* Prefix + separators: `dip1:` (5 chars) + second colon (1 char)
+* Algorithm token: `sha256` (6 chars)
+* Digest: 43 chars
+
+Total: 55 characters, fitting comfortably within the 64-byte requirement.
+
+For inline payloads, the combined length of `<type>` and `<base64url-payload>` MUST keep the string within 64 characters.
+
+## Rationale
+
+* Fixed namespace (`dip1`) prevents collisions with other project-defined encodings.
+* Algorithm tag enables future extensions without ambiguity.
+* Separating purpose metadata into the payload simplifies domain separation and allows richer payload structures.
+* Base64url encoding maximises information density while remaining safe for textual channels.
+
+## Implementation Notes
+
+* Existing digest libraries can be reused by serialising payloads as `<algo>:<base64url>` before prefixing with `dip1:`.
+* Canonical payload serialisation (e.g. `content-type:value`) should be specified by higher-level protocols.
+* Inline payloads are best suited for small tokens such as capability flags or truncated keys.
+
+## Security Considerations
+
+* Security strength is determined by the chosen algorithm (SHA-256 recommended).
+* Payload canonicalisation must be consistent to avoid digest mismatches.
+* Inline payloads are not hashed; consumers must validate them according to application policy.
+
+## Test Vectors
+
+| Case                      | Report data                                                     | Outband payload                                                                             |
+| ------------------------- | ---------------------------------------------------------------- | ------------------------------------------------------------------------------------------------ |
+| SHA-256 of payload        | `dip1:sha256:HmdI7tOxX-IxZngR8Aok9miZ4A5DzUj-HW-VUZ1Et0E`        | `ratls-pubkey:ee218f44a5f0a9c3233f9cc09f0cd41518f376478127feb989d5cf1292c56a01`                |
+| Inline ra-pk sample       | `dip1:inline:ra-pk:LPJNul-wow4m6DsqxbninhsWHlwfp0JecwQzYpOLmCQ` | _Embedded in identifier_                                                                        |
+| Inline alias (short form) | `dip1::ra-pk:LPJNul-wow4m6DsqxbninhsWHlwfp0JecwQzYpOLmCQ`       | _Embedded in identifier_                                                                        |
+
+## References
+
+* [Intel SGX DCAP Attestation Architecture](https://www.intel.com/content/www/us/en/developer/articles/technical/intel-software-guard-extensions-data-center-attestation-primitives.html)
+* [RFC 6920: Naming Things with Hashes (ni://)](https://www.rfc-editor.org/rfc/rfc6920)
+* [W3C Subresource Integrity (SRI)](https://www.w3.org/TR/SRI/)
+
+## Copyright
+
+Copyright and related rights waived via CC0.