What are trust models and how do they work in network security?

1 Direct Trust

Direct trust is the simplest and most basic form of trust model, where each entity in a network trusts only itself and those that it has explicitly verified. For example, if Alice wants to communicate with Bob, she needs to have a copy of Bob's public key and verify that it belongs to him. This way, Alice can encrypt and decrypt messages with Bob using his public key and her private key, and vice versa. Direct trust is suitable for small and closed networks, where the number of entities is limited and the trust relationships are stable.

2 Third-Party Trust

Third-party trust is a more common and scalable form of trust model, where each entity in a network trusts a central authority that vouches for the identities and credentials of other entities. For example, if Alice wants to communicate with Bob, she does not need to have a copy of Bob's public key or verify it herself. Instead, she can rely on a trusted third party, such as a certificate authority (CA), that issues and signs digital certificates for Bob and other entities. A digital certificate is a document that contains the public key and other information of an entity, such as its name, domain, and expiration date. A CA is a trusted entity that verifies the identity and legitimacy of an entity before issuing and signing a digital certificate for it. This way, Alice can verify Bob's identity and public key by checking his digital certificate and the signature of the CA. Third-party trust is suitable for large and open networks, where the number of entities is dynamic and the trust relationships are diverse.

3 Hierarchical Trust

Hierarchical trust is a variation of third-party trust, where there is a hierarchy of CAs that delegate their trust to lower-level CAs. For example, if Alice wants to communicate with Bob, she does not need to trust the CA that issued and signed Bob's digital certificate directly. Instead, she can trust a higher-level CA that has issued and signed the certificate of the CA that issued and signed Bob's certificate. This way, Alice can verify Bob's identity and public key by following a chain of certificates and signatures from the highest-level CA to the lowest-level CA. Hierarchical trust is suitable for complex and distributed networks, where the CAs are organized into different domains, regions, or levels.

4 Web of Trust

Web of Trust is another variation of third-party trust, where there is no central authority or hierarchy of CAs, but rather a network of peers that endorse and rate each other's identities and credentials. For example, if Alice wants to communicate with Bob, she does not need to trust a CA or a chain of CAs. Instead, she can trust other peers that have verified and vouched for Bob's identity and public key. These peers can be friends, colleagues, or other entities that Alice knows and trusts. Alice can also check the reputation and trustworthiness of these peers based on their ratings, feedback, and history. Web of Trust is suitable for decentralized and peer-to-peer networks, where the CAs are not available, reliable, or trustworthy.

5 Hybrid Trust

Hybrid trust is a combination of different trust models, where each entity in a network can choose the most appropriate trust model for its needs and preferences. For example, if Alice wants to communicate with Bob, she can use direct trust, third-party trust, hierarchical trust, or web of trust, depending on the situation, the availability of CAs or peers, and the level of security and convenience she requires. Hybrid trust is suitable for heterogeneous and adaptive networks, where the entities have different capabilities, requirements, and expectations.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?