When StrongSwan EAP-RADIUS plugin is in use, authentication delegated to RADIUS server. Actual EAP handshake occurs between VPN client and RADIUS server. [1] S

When StrongSwan EAP-RADIUS plugin is in use, authentication delegated to RADIUS server. Actual EAP handshake occurs between VPN client and RADIUS server. [1] Some EAP authentication methods (namely, EAP-MSCHAPv2 and EAP-TLS) export Master Session Key, which is exported to StrongSwan via MS-MPPE-Send-Key/MS-MPPE-Recv-Key EAP attributes. [2] So, MSK derived on RADIUS side and sent to StrongSwan. Eavesdropper with knowledge of RADIUS secret key capable to intercept and decrypt such EAP payload. [1] - https://wiki.strongswan.org/projects/strongswan/wiki/EAPRadius#EAP-Radius https://wiki.strongswan.org/projects/strongswan/wiki/EAPRadi... [2] - https://tools.ietf.org/html/rfc5216#section-2.3 https://tools.ietf.org/html/rfc5216#section-2.3