What Is Public-Key Cryptography?
Public-key cryptography uses a mathematically linked pair of keys — one public, one private — so that what one key does, only the other can undo. Anyone can encrypt to your public key, but only your private key decrypts; and only your private key can sign, while anyone can verify with the public one. Introduced by Diffie and Hellman in 1976, it is the basis of signatures, passkeys and most agent identity.
Why a pair changes everything
Before public-key cryptography, two parties had to share a secret in advance to communicate securely — a problem that does not scale to strangers. A key pair removes that: you publish one half and keep the other, so anyone can send you something only you can open, or verify something only you could have signed, with no prior contact.
For agents acting across organisations that never coordinated, this is the enabling primitive: identity and authority can be a key the actor holds, and verification is something anyone recomputes rather than a secret anyone must be trusted with.
Related standards
Questions
Is public-key cryptography the same as encryption?
It is a kind of it — asymmetric encryption — but it also enables signatures and key exchange, which are not encryption at all.
Why not just use it for everything?
It is slow for bulk data, so systems use it to exchange a fast symmetric key and encrypt the data with that.
Keep reading
By Michael Gord · published 2026-10-09 · part of the Agentic Encyclopedia. Dates are the day of publication; events are cited at their own dates.