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Clarify how reference hashes are done

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This commit is contained in:
Travis Ralston 2019-01-31 17:22:55 -07:00
parent 01556e5b17
commit ad64af3f01
2 changed files with 18 additions and 11 deletions
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13
specification/rooms/v3.rst
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@ -63,17 +63,8 @@ Event IDs
should be using. By removing the use of a dedicated event ID, servers are required
to track the hashes on an event to determine its ID.
The event ID is calculated using the following algorithm. Note that the hashing
algorithm used is the same as in previous room versions.
1. Redact the event.
2. Remove the `signatures` field from the event.
3. Serialize the event into `Canonical JSON`_.
4. Compute the hash of the JSON bytes.
5. Encode the sha256 hash using `Unpadded Base64`_.
6. Use the resulting string as the event ID prefixed with ``$``.
A resulting event ID using this approach should look similar to
The event ID is the reference hash of the event encoded using `Unpadded Base64`_,
prefixed with ``$``. A resulting event ID using this approach should look similar to
``$CD66HAED5npg6074c6pDtLKalHjVfYb2q4Q3LZgrW6o``.
Event IDs should not be sent over federation to servers when the room uses

16
specification/server_server_api.rst
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@ -1050,6 +1050,22 @@ been given a redacted version of the event. To enforce this, the receiving
server should use the redacted copy it calculated rather than the full copy it
received.
Calculating the reference hash for an event
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The *reference hash* of an event covers the essential fields of an event,
includuing content hashes. It is calculated as follows.
1. The event is put through the redaction algorithm.
2. The ``signatures``, ``age_ts``, and ``unsigned`` properties are removed
from the event, if present.
3. The event is converted into `Canonical JSON`_.
4. A sha256 hash is calculed on the resulting JSON object.
Calculating the content hash for an event
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~