CHAP is an improvement over PAP because the clear-text password is not sent over the link. Instead, the password is used to create a hash from the original challenge. The server knows the client’s clear-text password and can, therefore, replicate the operation and compare the result to the password sent in the client’s response. CHAP protects against replay attacks by using an arbitrary challenge string for each authentication attempt. CHAP protects against remote-client impersonation by unpredictably sending repeated challenges to the remote client throughout the duration of the connection.
PIA is another great option and offers a 7 day money back guarantee. It keeps no logs, which is a claim that it has proved in court! And although optional, its security can be first rate. Its desktop software supports multiple security options, a VPN kill switch, DNS leak protection, and port forwarding. Up to 5 simultaneous connections are permitted. Its Android client is almost as good, and PIA boasts excellent connection speeds. PIA has servers located in 29 other countries.
EAP-TLS is an IETF standard (RFC 2716 in the IETF RFC Database for a strong authentication method based on public-key certificates. With EAP-TLS, a client presents a user certificate to the server, and the server presents a server certificate to the client. The first provides strong user authentication to the server; the second provides assurance that the VPN client has reached a trusted VPN server. Both systems rely on a chain of trusted certification authorities (CAs) to verify the validity of the offered certificate.
While you're connected to a VPN, all your network traffic passes through this protected tunnel, and no one—not even your ISP—can see your traffic until it exits the tunnel from the VPN server and enters the public internet. If you make sure to only connect to websites secured with HTTPS, your data will continue to be encrypted even after it leaves the VPN.