Hi, I am working on the implementation of an EAP-SIM supplicant, when i send to freeradius a EAP-Response/SIM/Start packet i receive as expected an EAP-Resquest/SIM/Challenge with AT_RAND (RAND value was specified in users file [2]) and AT_MAC, after this I should calculate MAC value and test if this value matches witch AT_MAC value sent by freeradius. my question is how freeradius calculate MAC value in AT_MAC atribute ? or from wich source freeradius fill MAC value in the AT_MAC attribute ? [2]: my eap-sim user is set in users file as below : 1262074920549791 Auth-Type := EAP, EAP-Type := SIM EAP-Sim-Rand1 = 0x39900000000000000000000000000000, EAP-Sim-SRES1 = 0x30112233, EAP-Sim-KC1 = 0x445566778899AABB, EAP-Sim-Rand2 = 0x31000000000000000000000000000000, EAP-Sim-SRES2 = 0x31112233, EAP-Sim-KC2 = 0x445566778899AABB, EAP-Sim-Rand3 = 0x32000000000000000000000000000000, EAP-Sim-SRES3 = 0x32112233, EAP-Sim-KC3 = 0x445566778899AABB Thank you in advance, Best regards. -- Sami