answers: untrusted external network
context: in modern messengers like WhatsApp and Signal, which achieve usable end-to-end encryption in a similar way, effectively preventing surveillance of the content of encrypted messages by a passive attacker. Autocrypt tries to maximize the possible opportunities for encryption, but is not aggressive about encrypting messages at all possible opportunities. Instead, encryption is only enabled by default if all communicating parties consent, allowing users to make themselves available for encrypted communication without getting in the way of their established workflows. Active attacks, which can only be performed in a targeted fashion and require a more capable attacker, are not directly prevented. </s> Firewall (computing) In computing, a firewall is a network security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules. A firewall typically establishes a barrier between a trusted internal network and untrusted external network, such as the Internet. Firewalls are often categorized as either network firewalls or host-based firewalls. Network firewalls filter traffic between two or more networks and run on network hardware. Host-based firewalls run on host computers and control network traffic in and out of those machines. The term "firewall" originally referred to a wall intended to confine a fire within a </s> the UK’s University of Oxford, Australia's Queensland University of Technology, and Canada’s McMaster University published a formal analysis of the protocol. They concluded that the protocol was cryptographically sound. The protocol provides confidentiality, integrity, authentication, participant consistency, destination validation, forward secrecy, post-compromise security (aka future secrecy), causality preservation, message unlinkability, message repudiation, participation repudiation, and asynchronicity. It does not provide anonymity preservation and requires servers for the relaying of messages and storing of public key material. The Signal Protocol also supports end-to-end encrypted group chats. The group chat protocol is a combination of a pairwise double ratchet and multicast encryption.
question: fire wall is used in communication to save from