IPSEC
A set of protocols developed by the IETF to support secure exchange of packets using IP. IPSec supports two encryption modes, Transport, that encrypts only the payload of each packet , but leaves the header untouched, and Tunnel, the more secure mode that encrypt both the header and the payload. For IPSec to work, the sending and recieving must share a public key. IPSec has been deployed widely to implement Virtual Private Network (VPNs).
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