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Add section on flow & negotiated topic

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Andrea Maria Piana 2020-03-26 13:20:08 +01:00 committed by Oskar Thoren
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status-whisper-usage-spec.md
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@ -157,7 +157,7 @@ for i = 0; i < topicLen; i++ {
### Partitioned topic
Whisper is broadcast-based protocol. In theory, everyone could communicate using a single topic but that would be extremaly inefficient. Opposite would be using a unique topic for each conversation, however, this brings privacy concerns because it would be much easier to detect whether and when two parties have an active conversation.
Whisper is broadcast-based protocol. In theory, everyone could communicate using a single topic but that would be extremely inefficient. Opposite would be using a unique topic for each conversation, however, this brings privacy concerns because it would be much easier to detect whether and when two parties have an active conversation.
Partitioned topics are used to broadcast private messages efficiently. By selecting a number of topic, it is possible to balance efficiency and privacy.
@ -181,8 +181,6 @@ for i = 0; i < topicLen; i++ {
}
```
If partitioned topic support is enabled by the Status client, it MUST listen to its paritioned topic. It MUST be generated using the algorithm above and active public key.
### Public chats
A public chat MUST use a topic derived from a public chat name following the algorithm below:
@ -232,14 +230,49 @@ Generic discovery topic is a legacy topic used to handle all one-to-one chats. T
Generic discovery topic MUST be created following [Public chats](#public-chats) topic algorithm using string `contact-discovery` as a name. -->
### One-to-one topic
In order to receive one-to-one messages incoming from a public key `P`, the Status Client MUST listen to a [Contact Code Topic](#contact-code-topic) created for that public key.
### Group chat topic
Group chats does not have a dedicated topic. All group chat messages (including membership updates) are sent as one-to-one messages to multiple recipients.
### Negotiated topic
When a client sends a one to one message to another client, it MUST listen to their negotiated topic. This is computed by generating
a diffie-hellman key exchange between two members and taking the first four bytes of the `SHA3-256` of the key generated.
```golang
sharedKey, err := ecies.ImportECDSA(myPrivateKey).GenerateShared(
ecies.ImportECDSAPublic(theirPublicKey),
16,
16,
)
hexEncodedKey := hex.EncodeToString(sharedKey)
var hash []byte = keccak256(hexEncodedKey)
var topicLen int = 4
if len(hash) < topicLen {
topicLen = len(hash)
}
var topic [4]byte
for i = 0; i < topicLen; i++ {
topic[i] = hash[i]
}
```
A client SHOULD send to the negotiated topic only if it has received a message from all the devices included in the conversation.
### Flow
To exchange messages with client B, a client A SHOULD:
- Listen to client's B Contact Code Topic to retrieve their bundle information, including a list of active devices
- Send a message on client's B partitioned topic
- Listen to the Negotiated Topic between A & B
## Message encryption
Even though, the protocol specifies an encryption layer that encrypts messages before passing them to the transport layer, Whisper protocol requires each Whisper message to be encrypted anyway.