Public key cryptography

Public key cryptography, also called asymmetric encryption, uses a pair of keys – one public, one private – to securely exchange data. The public key is shared openly, while the private key is kept secret. Anything encrypted with one key can only be decrypted with the other.  

In email, this cryptographic model shows up in two major places:  

• Encryption protocols like TLS use public key cryptography to protect messages in transit.  

• Authentication standards like DKIM rely on it to sign outgoing messages with a private key that inbox providers can verify using the public key published in DNS.  

This model ensures messages haven’t been altered and really come from who they claim to, building trust with ISPs and recipients alike. In short, public key cryptography is how your email proves it’s you and not a spoof.