Which of the following is NOT an encryption method used by VPNs (Virtual Private Networks)?

IPSEC (IP Security) is a widely used suite of protocols for securing IP communications, providing encryption and authentication, and is fundamental to many VPN implementations.

L2F (Layer 2 Forwarding) is a tunneling protocol, often combined with encryption within a VPN architecture to secure traffic, even if it doesn't provide encryption itself.

L2TP (Layer 2 Tunneling Protocol) is a tunneling protocol that relies on IPsec for encryption and authentication, thus being integral to secure VPNs.

SSH (Secure Shell) is a protocol that can establish secure tunnels, which can be used to create VPN-like secure connections, providing strong encryption.

PPTP (Point-to-Point Tunneling Protocol) is a VPN tunneling protocol that includes encryption methods, though its security has been largely deprecated due to known vulnerabilities.

All the listed options are either direct encryption protocols (like IPsec, SSH when used for tunneling) or tunneling protocols that are fundamental components of VPNs and are either combined with encryption (L2TP with IPsec, L2F historically within a secure system) or provide their own encryption (PPTP with MPPE), meaning they are all associated with securing VPN communications.