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Public Key Cryptography

A key is a piece of information, usually a string of numbers or letters

If you use a single key, its symmetric cryptography

Public-key, or asymmetric cryptography, is a system that uses pairs of keys based on mathematical one-way functions

There are two keys, one public, one private, they are a pair

Only the private key can decrypt a message which is encrypted with its public key

And public key can verify if a message is signed with its private key

eg.

1. Alice and Bob shares their public keys in the open,

Bob

1. writes a message to Alice
2. signs it with his private key
3. encrypts it using Alice’s public key and

Alice

1. Gets the encrypted message
2. Opens it using her private key
3. Verifies the signature using Bob’s public key

https://en.wikipedia.org/wiki/Diffie%E2%80%93Hellman_key_exchange