sequenceDiagram
    actor C as Client
    participant S as Server

    note over C,S: Assume the user has already logged in <br> and is in possession of the parent folder key and the file key

    C->>S: Ask for Guest's public key
    S-->>C: Send Guest's public key

    C->>C: Encrypt file's key with Guest's public key

    C->>S: Send encrypted Guest's file key for file