# public key cryptography

n.A technique to encrypt and decrypt messages using a pair of different keys.
### Notes

Because the key used to decrypt a message cannot be deduced from the key used to encode a message, the encoding key can be made public. Anyone can use an individual's public key to encrypt a message that only the individual can decrypt using the private key. Public key cryptography was a breakthrough because it was the first technology that did not require keys be exchanged in advance. Two individuals, each with their own public and private keys, can send each other messages that are completely confidential. Alice sends Bob messages using Bob's public key; only Bob has the key to decrypt and read her messages. Bob sends Alice messages using Alice's public key; only Alice has the private key to read his messages.Public key cryptography can be used to authenticate the sender of a message. A message encoded with the private key can be decrypted with the public key. If Alice receives an encrypted message that can be read with Bob's public key and if she has confidence that the public key is Bob's, then she can have equal confidence that the message is from Bob. A certificate authority serves as a trusted third party to give Alice confidence in Bob's public key.
### Citations

Levy, S., 2001, p. 70 Instead of using one single secret key, you could use a key pair. The tried-and-true symmetrical key would be replaced by a dynamic duo. One would be able to do the job of scrambling a plaintext message – performing the task in such a way that outsiders couldn't read it – but a secret trapdoor would be built into the message. The other portion of the key pair was like a latch that could spring open that trapdoor and let its holder read the message. And here was the beauty of the scheme: yes, that second key – the one that flipped open the trapdoor – was of course something that had to be kept under wraps, safe form the prying hand of potential eavesdroppers. But its mate, the key that actually performed the encryption, didn't have to be a secret at all. In fact, you wouldn't want it to be secret. You'd be happy to see it distributed far and wide.