Which protocol is used for setting up secure channels between two devices, typically in VPNs?

PPP (Point-to-Point Protocol) is a data link layer protocol for direct two-point serial connections and does not provide encryption or the key exchange mechanisms needed to establish secure VPN tunnels.

IPSec (Internet Protocol Security) operates at the network layer and provides authentication and encryption for IP packets using two core protocols: AH (Authentication Header) for integrity and ESP (Encapsulating Security Payload) for confidentiality. It uses IKE (Internet Key Exchange) to negotiate security associations, making it the primary technology for site-to-site and remote-access VPNs.

PEM (Privacy Enhanced Mail) is a Base64 encoding format used to store cryptographic keys and certificates, not a protocol for negotiating or establishing secure communication channels.

SET (Secure Electronic Transaction) was a protocol designed specifically for securing credit card transactions over the internet, not for creating general-purpose secure network channels or VPNs.