pEpEngine/codegen/sync_protocol.md

p≡p Sync protocol

Protocol Stack

Key Sync | Trust Sync | Contact Sync | Task Sync

• | - | - | - Sync Baseprotocol Transport

Forming a Device Group with Key Sync

Sender

A Sender is the Person sending a message. In case of M2M it is the Operating Entity of the Device sending.

Device

A Device is an entitiy, which is sending representative of a Sender.

State Sole

A Device is in state Sole when it is not member of a Device group and when it is not part of a Negotiation.

State Grouped

A Device is in state Grouped when it is member of a Device group and when it is not part of a Negotiation.

Negotiation as a Transaction

TID

A TID (transaction ID) is a UUID version 4 variant 1.

Challenge

The Challenge is identified by a TID. The Challenge is being set by each Beacon and must be repeated in a corresponding Negotiation Request. The Challenge has two functions:

1. The Challenge makes it possible to filter out own Beacons
2. The Challenge makes it necessary to be able to read the communication channel (usually an Inbox), otherwise Beacons cannot be answered

Negotiation

A Negotiation is a Transaction identified by a TID. The Negotiation's TID is the XOR of the two Challenge TIDs of the two devices, respectively.

Roles and Keys

Sender signing

The key with which the Sender of the message is signing. In case of trusted messages this is signalled within the encrypted message. This is signalled by by opt_field pEp-sender-sign, which is not reflected to the outer message.

Transports can opt to use HMAC or OMAC instead of digital signatures.

Transport signing

Keys with which others and not the Sender are signing a message.

Sender Group key

A Sender Group Key is a Sender's signing key, which is used to update the Device Group information. If it is reset the Device Groups breaks.