Certificate authority (CA)
termcryptographysecurity
An organisation trusted by browsers and operating systems to vouch that a public key belongs to a given name. The set of them a client trusts is its root store - on the order of a hundred-plus organisations across many jurisdictions.
The uncomfortable property is that the model is a flat list: by default any authority in the store can issue for any name anywhere, so the security of every site depends on the weakest member. The counterweights arrived late and from outside the authorities themselves - browser root programmes that set and enforce rules, CAA records that let a domain restrict who may issue for it, and public logging that makes issuance observable. Judge a CA less by its cryptography than by its validation process and its incident history.
Also known as: autoridade certificadora, root store, trust store, ca/browser forum