Public-key cryptography

Public-key cryptography, or asymmetric cryptography, is the field of cryptographic systems that use pairs of related keys. Each key pair consists of a public key and a corresponding private key. Key pairs are generated with cryptographic algorithms based on mathematical problems termed one-way functions. Security of public-key cryptography depends on keeping the private key secret; the public key can be openly distributed without compromising security.
— Wikipedia

Examples of protocols using asymmetric key algorithms include:

• S/MIME
• GPG, an implementation of OpenPGP, and an Internet Standard
• EMV, EMV Certificate Authority
• IPsec
• PGP
• ZRTP, a secure VoIP protocol
• Transport Layer Security standardized by IETF and its predecessor Secure Socket Layer
• SILC
• SSH
• Bitcoin
• Off-the-Record Messaging

References

• GPG
• Public Key Cryptography - Computerphile - YouTube
• A (relatively easy to understand) primer on elliptic curve cryptography | Ars Technica