Chain of trust is a
design principle in
security systems, in which a set of
nodes is linked by a set of
trust relationships. Each node trusts an adjacent node;
message passing falls across these
trust links, so that two entities without a direct set of trust can communicate.
Huh?
You want to authorize an automatic payment from your bank account. Using your online account, you click appropriately, and it's been set up. But let's look at the chain of trust.
Through your browser, you typed in your password. Now, the web server at the hosting company trusts that you are, in fact, you. The web server is just a front end to a database server, however. The web server sends a message to the database saying, "So-and-so wants to make this transaction." The database trusts the web server. Every day, the database sends a list of transactions to the bank. Including in this list is a message saying, "Transfer xxx USD from so-and-so to Alyssa P. Hacker." The bank trusts the database, and sends the money off.
Unlike transitive trust, in which the bank would end up trusting you without knowing, the chain of trust is used to validate some message being passed through.