MPPE

MPPE, short for Microsoft Point-to-Point Encryption, is an encryption protocol used to protect the payload of PPP frames carried within PPTP tunnels. Developed by Microsoft, MPPE provides confidentiality for data transmitted over connections that use Point-to-Point Tunneling Protocol. MPPE is described in IETF RFC 3078 and is integrated with PPTP as part of the PPP security model, with authentication handled by the underlying PPP mechanism (for example MS-CHAP or EAP).

Operation and keying: MPPE uses the RC4 stream cipher to encrypt payload data and derives session keys from the PPP authentication material. It supports two main encryption strengths: 40-bit and 128-bit RC4 keys, allowing deployment to meet policy or regulatory requirements. Per-session keys can be applied independently for inbound and outbound directions.

Security and status: MPPE and PPTP rely on RC4 and the PPTP design, both of which have known weaknesses. Modern cryptographic practice generally discontinues PPTP/MPPE in favor of more secure VPN technologies such as IPsec, OpenVPN, or WireGuard. If MPPE is used, it should be complemented by strong authentication and up-to-date software, and deployments should assess current security guidance and compatibility requirements.

History and usage: MPPE emerged in the 1990s as part of PPTP to provide encrypted remote access. It saw widespread deployment with Windows NT/2000 and subsequent Windows versions. Over time, it has declined in favor of more secure VPN technologies but remains supported primarily for backward compatibility in many systems.