Public Key Cryptography
Today's asymmetric or public key cryptography systems are a significant development over conventional symmetric cryptography systems in that they permit two parties to swap data privately in the existence of possible eavesdroppers, without earlier agreeing on a "shared secret." Such a system is a called "asymmetric" because it is based on the thought of a matched cryptographic key pair in which a cryptographic key is no longer a simple "shared secret," but rather is divide into two sub keys, the private key and public key.
Abstractly, a participant wanting to receive encrypted communications using an asymmetric cryptography system first generates such a key pair, keeping the private-key portion as a secret and "publishing" the public-key portion to all parties that want to encrypt data for that participant. Because enciphering data requires only access to the public key, and decrypting data requires the private key, such a system in principle can sidestep the first layer of difficulty in the key organization problem because no common secret need be exchanged.