As part of our research, we also make sure to find out where the company is based and under what legal framework it operates. Some countries don't have data-retention laws, making it easier to keep a promise of "We don't keep any logs." It's also useful to know under what circumstances a VPN company will hand over information to law enforcement and what information it would have to provide if that should happen.
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.
Authentication that occurs during the creation of a PPTP-based VPN connection uses the same authentication mechanisms as PPP connections, such as Extensible Authentication Protocol (EAP), Microsoft Challenge-Handshake Authentication Protocol (MS-CHAP), Microsoft Challenge-Handshake Authentication Protocol version 2 (MS-CHAP v2), CHAP, Shiva Password Authentication Protocol (SPAP), and Password Authentication Protocol (PAP). PPTP inherits encryption, compression, or both of PPP payloads from PPP. For PPTP connections, EAP-Transport Layer Security (EAP-TLS), MS-CHAP, or MS-CHAP v2 must be used for the PPP payloads to be encrypted using Microsoft Point-to-Point Encryption (MPPE).
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.