Once a message chain is established, Loki enforces Perfect Forward Secrecy and Deniable Authentication. PFS enables resistance from attacks where a long-term key is exposed. A new shared encryption key is used for each session, so if a single session key is revealed, the whole message chain is not compromised. DA refers to the ability for two parties to prove to each other that they are the sender of each new message.

Messenger Encryption

Authentication of users is important to ensure protection against 'man in the middle' attacks. Loki uses Pre-Shared Key authentication  where users have multiple options for the establishment of a PSK. They can establish a key out of band, or alternatively, they can agree on a PSK over Loki by asking the other a question which no third-party would know the answer. 

User Authentication

- Messenger Encryption
- User Authentication

University of Connecticut

- Messenger Routing
- Online Messaging
- Offline Messaging
- Messenger Encryption and Authentication

Loki Messenger Elements

https://loki.network/wp-content/uploads/2018/10/LokiWhitepaperV3_1.pdf

Loki Whitepaper

Message routing on Loki depends on if the receiving party is online or offline. When both users on online, higher bandwidth communication can take place as the message do not need to be stored on service nodes. A public key acts as both a long term encryption key and a routing address. In order to ensure protection against a 'man in the middle' attack, this key should be exchange out-of-band, either in person or through another secure exchange mode. 

Messenger Routing

Once a person has the other's public key, they can create a path towards them by querying the DHT of any service node and obtaining the introduction set corresponding with the other's public key. Once finding the introduction set, the initial user can choose three random Service Nodes to act as an intermediary hops between their and the receivers. The path is now established, and the two can exchange messages with high level privacy. 

Online Messaging

Offline routing uses a modified version of Postal Services over Swarm. Swarms are logical groupings of Service Nodes, based both on their public keys and the hash of the block that their staking transaction first appeared in. Each swarm has a swarmID and consists of nine nodes. The sending user must calculate which swarm the receiver belongs do, done using the public key. They can then anonymously route a message through the network to a random Service Node in that swarm. That Service Node will then distribute that message to the other 8 nodes in the swarm, all of which store the messages for their allocated time-to-live. The receiver can then query any two nodes in the swarm for messages that he can decrypt.  

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