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Harden topic serialization

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Alex Stokes 2021-06-08 14:15:57 -05:00
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specs/altair/p2p-interface.md
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@ -77,11 +77,13 @@ The specification around the creation, validation, and dissemination of messages
The derivation of the `message-id` has changed starting with Altair to incorporate the message `topic` along with the message `data`. These are fields of the `Message` Protobuf, and interpreted as empty byte strings if missing.
The `message-id` MUST be the following 20 byte value computed from the message:
* If `message.data` has a valid snappy decompression, set `message-id` to the first 20 bytes of the `SHA256` hash of
the concatenation of `MESSAGE_DOMAIN_VALID_SNAPPY` with the snappy decompressed message data and the topic name,
i.e. `SHA256(MESSAGE_DOMAIN_VALID_SNAPPY + snappy_decompress(message.data) + message.topic)[:20]`.
the concatenation of the following data: `MESSAGE_DOMAIN_VALID_SNAPPY`, the length of the topic byte string (encoded as little-endian `uint64`),
the topic byte string, and the snappy decompressed message data:
i.e. `SHA256(MESSAGE_DOMAIN_VALID_SNAPPY + uint_to_bytes(uint64(len(message.topic))) + message.topic + snappy_decompress(message.data)[:20]`.
* Otherwise, set `message-id` to the first 20 bytes of the `SHA256` hash of
the concatenation of `MESSAGE_DOMAIN_INVALID_SNAPPY` with the raw message data and the topic name,
i.e. `SHA256(MESSAGE_DOMAIN_INVALID_SNAPPY + message.data + message.topic)[:20]`.
the concatenation of the following data: `MESSAGE_DOMAIN_INVALID_SNAPPY`, the length of the topic byte string (encoded as little-endian `uint64`),
the topic byte string, and the raw message data:
i.e. `SHA256(MESSAGE_DOMAIN_INVALID_SNAPPY + uint_to_bytes(uint64(len(message.topic))) + message.topic + message.data)[:20]`.
The new topics along with the type of the `data` field of a gossipsub message are given in this table: