Channels¶

Channels are read-only broadcast conversations where only authorized authors can post.

Overview¶

Property	Value
Read Access	Anyone can subscribe
Write Access	Authorized authors only
Encryption	AES-256-GCM with channel key
Routing	Topic-based (interest filter)

Conversation Types¶

Type	Read	Write	Example
GROUP	Members only	Any member	Private chat groups
CHANNEL	Anyone	Authorized authors	News feeds, announcements
BROADCAST	All mesh	All mesh	Mesh-wide alerts

Channel Kinds¶

Kind	Transport	Range	Status
`MESH_LOCAL`	Nearby only	Local mesh	Implemented
`GLOBAL`	Nostr relays	Global	Future

Channel Descriptor¶

Each channel has a descriptor containing: - id - Channel identifier - kind - MESH_LOCAL or GLOBAL - displayName - Human-readable name - description - Optional description - ownerUidHex - Channel owner's UID - conversationType - CHANNEL, GROUP, or BROADCAST - isPrivate - Whether the channel is private

Computed Properties¶

Property	Derivation
`topicKey`	SHA256(channelId) - 32 bytes
`shortId`	base32(topicKey[:6]) - 10 chars
`isGroup`	conversationType == GROUP
`isChannel`	conversationType == CHANNEL
`isBroadcast`	conversationType == BROADCAST

Mesh Broadcast Channel¶

A special built-in channel for mesh-wide broadcasts.

Characteristics¶

Property	Value
Channel ID	`channel:mesh_local`
Kind	MESH_LOCAL
Encryption	None (plaintext)
Author verification	Signature check

Payload¶

Each broadcast contains: - Message text - Sender UID - Sender display name - Timestamp

Channel vs Group Comparison¶

Aspect	Channel	Group
Write permission	Authorized authors	Any member
Membership	Subscribe (anyone)	Join (invite or public)
Key distribution	From owner	Via invite
Content encryption	Yes	Yes
Author signature	Required	Required

Subscription¶

Subscribing to a channel adds its topic to the interest filter. When bundles arrive with matching topics, they are delivered to subscribers.

Message Flow¶

Publishing (Author)¶

sequenceDiagram
    participant Author as Author
    participant Crypto as Crypto
    participant DTN as DTN Layer

    Author->>Crypto: Sign message
    Crypto-->>Author: signature
    Author->>Crypto: Encrypt with channel key
    Crypto-->>Author: ciphertext
    Author->>DTN: Send bundle (dstTopic=channelTopic)

Receiving (Subscriber)¶

sequenceDiagram
    participant DTN as DTN Layer
    participant Filter as Interest Filter
    participant Crypto as Crypto
    participant Sub as Subscriber

    DTN->>Filter: Check topic match
    Filter-->>DTN: Match found
    DTN->>Crypto: Decrypt with channel key
    Crypto-->>DTN: plaintext
    DTN->>Crypto: Verify author signature
    Crypto-->>DTN: Valid
    DTN->>Sub: Deliver message

Author Verification¶

Only messages from authorized authors are accepted. Each channel maintains a list of authorized author UIDs, and incoming messages are verified against this list.

TTL¶

Message Type	TTL
Channel broadcast	4 hours (14400s)

Next: Private Groups | Membership CRDT