RFC0013: Multihash

Signed-off-by: Arnau Siches <arnau.siches@digital.cabinet-office.gov.uk>

content/multihash/index.md

@@ -0,0 +1,64 @@
+---
+rfc: 0013
+start_date: 2018-08-13
+pr: openregister/registers-rfcs/pull/26
+status: draft
+---
+
+# Multihash
+
+## Summary
+
+This RFC proposes to change the method to qualify hashes from using prefixes
+`sha-256:` to using [Multihash](https://multiformats.io/multihash/).
+
+**This RFC is not backwards compatible in the same sense as
+[RFC0010](https://github.com/openregister/registers-rfcs/pull/24)**
+
+## Motivation
+
+Currently, the specification defines a custom `sha-256:` prefix for
+stringified hexadecimal hashes to qualify them as SHA256. With this approach
+parsers must be done specifically for registers and registers must standarise
+any hashing algorithm needed by users. Relying on a standard helps benefiting
+from that standards ecosystem.
+
+## Explanation
+
+The proposal is to adopt [Multihash](https://multiformats.io/multihash/).
+Their specification is quite thorough but the gist is to replace any of our
+`sha-256:` to `1220`. `0x12` for the hashing function sha2-256 and `0x20` for
+the digest length.
+
+For example, instead of the current JSON:
+
+```json
+[{
+ "index-entry-number":"6",
+ "entry-number":"6",
+ "entry-timestamp":"2016-04-05T13:23:05Z",
+ "key":"GB",
+ "item-hash":["sha-256:6b18693874513ba13da54d61aafa7cad0c8f5573f3431d6f1c04b07ddb27d6bb"]
+}]
+```
+
+We will use
+
+```json
+[{
+ "index-entry-number":"6",
+ "entry-number":"6",
+ "entry-timestamp":"2016-04-05T13:23:05Z",
+ "key":"GB",
+ "item-hash":["12206b18693874513ba13da54d61aafa7cad0c8f5573f3431d6f1c04b07ddb27d6bb"]
+}]
+```
+
+And similarly, the `GET /items/{hash}` endpoint will expect something like
+this:
+
+```http
+GET /items/12206b18693874513ba13da54d61aafa7cad0c8f5573f3431d6f1c04b07ddb27d6bb HTTP/1.1
+Accept: application/json
+}]
+```