VPN Encryption and Integrity
IPsec security algorithms: AES (Advanced Encryption Standard) for encryption — AES-128, AES-192, AES-256. AES-256 is the current gold standard. SHA-2 (SHA-256, SHA-384, SHA-512) for integrity — replaces weak SHA-1 and MD5. Perfect Forward Secrecy (PFS): generates unique session keys for each VPN session — even if the long-term key is compromised, past session traffic cannot be decrypted. Always enable PFS for sensitive VPN traffic.
IKE versions: IKEv1 (older, more complex, multiple modes) vs IKEv2 (simpler, faster, more secure, supports MOBIKE for mobile clients). Use IKEv2 where possible. IKE negotiates the Security Association (SA) — the agreed encryption, integrity, and key-exchange parameters for the tunnel.
Deprecated/weak VPN protocols: PPTP — RC4/MPPE encryption, completely compromised — never use. L2TP alone — no encryption at all. 3DES — deprecated, vulnerable. MD5 — weak hash. Always use AES + SHA-2 + IKEv2 for IPsec VPNs.
VPN Authentication Security
VPN authentication methods ranked by security: Pre-shared key (PSK) — weakest, shared secret, vulnerable to brute force if key is weak. Certificate-based (X.509) — much stronger, uses asymmetric cryptography, mutual authentication. Multi-factor authentication — adds OTP or push notification on top of credentials. RADIUS/LDAP integration — enables per-user authentication with corporate directory.
Split tunneling security risks: when only corporate traffic goes through the VPN, internet traffic bypasses security controls. Malware on the endpoint could use the VPN connection to reach corporate resources while the internet connection is unmonitored. Full tunnel VPN routes all traffic through corporate security stack — higher protection, higher bandwidth cost.
Always-on VPN: endpoints always maintain VPN connection — closes the window when users are off-VPN and unprotected. Prevents bypassing security controls. Required for high-security environments.