Microsoft Point-to-Point Encryption - Definition from the Hotspot Shield Glossary
This proprietary method developed by Microsoft allows data to be encrypted and transferred across the P2P protocol (Point to Point) or PPTP VPN connections. MPPE secures the data between the connection and the tunnel server.
The data is encrypted using the RSA algorithm (Rivest, Ahamir, Aldeman) and can use both 40bit, 56bit and 128bit keys which are regularly changed to increase security. While MPPE does not alter the data’s level of compression in any way (either compressed or expanded), it is often used with MPPC (Microsoft Point to Point Compression) which provides this functionality. Microsoft Point to Point Encryption guidelines are laid out in IETF’s RFC 3078.