Public key infrastructure (PKI) is a catch-all term for everything used to establish and manage public key cryptography. Related is the key sharing problem.

For example, it can help ensure that all peers in the network know each other’s public keys (i.e. that public keys are… public knowledge)

Private KeyPublic Key
Stays secret on your deviceShared with all your peers on the network
Acts like a password — only you have it, and it’s necessary for proving ownership of your public keyActs like a User ID — people publicly know about this to identity you
Can create signatures — unforgeable, tamper-evident certifications that you created that dataAllows others to verify the integrity of your signature
A mailbox key — allows you to open messages that only you can seeA mail slot — allows others to send you data only you can see


Pretty Good Privacy

A sort of web of trust protocol where you determine whether to trust another party based on who else you know has trusted that party.

As time goes on, you will accumulate keys from other people that you may want to designate as trusted introducers. Everyone else will each choose their own trusted introducers. And everyone will gradually accumulate and distribute with their key a collection of certifying signatures from other people, with the expectation that anyone receiving it will trust at least one or two of the signatures. This will cause the emergence of a decentralized fault-tolerant web of confidence for all public keys.

The web of trust mechanism has advantages over a centrally managed public key infrastructure scheme