Hashes, Signatures and Certificates
A cryptographic hash gives a short fingerprint that is impractical to forge a match for, which makes tampering detectable. Signing a hash with a private key proves who produced it, and a certificate is that signature applied to the claim that a key belongs to a name.
What a learner can do afterwards
- Say what property of a hash makes it usable for detecting tampering
- Explain what a signature proves and what it does not
- Follow a certificate chain up to a root and say what trust is being placed where
1 · Read
A hash is a short fingerprint of some data. Change one letter and the fingerprint comes out completely different. It is impractical to craft a different input with the same fingerprint, so when you recompute it, tampering stands out.
A signature is that fingerprint signed with someone's private key, which anyone checks with the matching public key. It proves who produced the statement. It does not prove the statement is true or the site is safe. A certificate applies that signature to the claim that a key belongs to a name.
Your browser climbs the chain link by link: each signature, the requested name, and the dates. Trust lands on the root stored in your computer, not on the website alone.
A signature names its author and no one else. Only the private-key holder could have signed it, checked with the public key, so the signature proves who produced the statement. It says nothing about truth.
A certificate signs one claim: a key belongs to a name. Design and price are never signed. Read the signed line to see the binding.
Hashes expose change, signatures name the author, and the chain moves your trust up to a root you already hold.
2 · Watch
Take it off screen
Where it sits
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.