oo Challenge-response authentication numerous protocol-based techniques for realizing authentication the basic protocol constructions, such as C-R techniques, in particular those which should be regarded as good ones and the simple technical ideas behind the good constructions, are not so diverse freshness or liveness are the most basic goals 復大辱软件学院 LiST
LiJT 11 Challenge-response authentication • numerous protocol-based techniques for realizing authentication • the basic protocol constructions, such as C-R techniques, in particular those which should be regarded as good ones, and the simple technical ideas behind the good constructions, are not so diverse. • freshness or liveness are the most basic goals
oo Challenge-response authentication Alice is identified by a secret she possesses Bob needs to know that alice does indeed possess this secret Alice provides response to a time-variant challenge(nonce Number used ONCE Response depends on both secret and challenge To defense sniffer attack 12 復大辱软件学院 LiST
LiJT 12 Challenge-response authentication • Alice is identified by a secret she possesses • Bob needs to know that Alice does indeed possess this secret • Alice provides response to a time-variant challenge (Nonce, Number used ONCE) • Response depends on both secret and challenge • To defense sniffer attack
eag Challenge-response authentication Using Symmetric encryption One way functions Public key encryption Digital signatures 復大辱软件学院 LiST
LiJT 13 Challenge-response authentication Using • Symmetric encryption • One way functions • Public key encryption • Digital signatures
o using Symmetric Key Encryption Alice and Bob share a key Ka Challenge Alice Alice, E(KA Challenge Bob server A Okay 復大辱软件学院 LiST
LiJT 14 using Symmetric Key Encryption • Alice and Bob share a key KA Alice KA Bob Server KA, Kc, Kd, …… Alice, E(KA, Challenge) Okay Challenge
ef Unilateral: Using random numbers Bob→>Ace:b Aice→>Bob:Ek(rb,B Bob checks to see if r is the one it sent out Also checks"B"-prevents reflection attack rb must be non-repeating, random prevents replay attack 15 復大辱软件学院 LiST
LiJT 15 Unilateral: Using random numbers • Bob ® Alice: rb • Alice ® Bob: EK(rb, B) • Bob checks to see if rb is the one it sent out – Also checks “B” - prevents reflection attack • rb must be non-repeating, random – prevents replay attack