chainoftrust

The chain of trust is a security model in which trust is established and propagated through a hierarchy of authorities. It relies on one or more trusted roots, known as trust anchors, and a sequence of certificates that link an end-entity (such as a website, software, or device) to a root certificate.

In PKI terms, a certificate is signed by its issuer, creating a chain from a trusted root certificate to intermediate certificates and then to the leaf certificate. The system must verify the entire chain, the signatures, the validity periods, and the revocation status before accepting the end-entity as trusted.

The verification process depends on platform policy and may involve checking a certificate revocation list (CRL) or using OCSP, plus ensuring the root certificate is present in a trusted store. Hardware roots of trust or secure elements may serve as the root to protect private keys and strengthen the chain.

Common applications include TLS for securing web traffic, code signing to ensure software integrity, and secure boot processes that verify firmware and operating system components during startup. In these contexts, trust is transferred from the root to intermediate authorities and finally to the software or data being verified.

Challenges include key compromise and management of long-lived root keys, certificate expiration, revocation delays, and supply chain risks where trusted components or certificates are subverted. The concept is policy-dependent; trust anchors differ by platform or organization, and the chain of trust is a model rather than a universal standard. See also PKI, certificates, TLS, code signing, and Secure Boot.