Reflection attack A reflection attack is a method of attacking a challenge-response authentication system that uses the same protocol in both directions. That is, the same challenge-response protocol is used by each side to authenticate the other side Challenge-response reflection attack Where N is a challenge I(A): N (A)→B:N B (A): EKIN (A)→B:Ek/N 復大辱软件学院 LiST
LiJT 16 Reflection attack • A reflection attack is a method of attacking a challenge-response authentication system that uses the same protocol in both directions. That is, the same challenge-response protocol is used by each side to authenticate the other side. • Challenge-response reflection attack Where N is a challenge • B → I(A): N I(A) → B: N B → I(A): EK{N} I(A) → B: EK{N}
Hey A variation for mechanism Bob→>Aice:Ek(rh,B Alice> Bob: rb Bob accepts if returned r, is correct rejects, otherwise 復大辱软件学院 LiST
LiJT 17 A variation for mechanism • Bob ® Alice: EK(rb, B) • Alice ® Bob: rb • Bob – accepts, if returned rb is correct – rejects, otherwise
el Unilateral: Using timestamps Time-Based Implicit challenge Aice→Bob:Ek(th,B Bob decrypts and verified that timestamp is OK Parameter b prevents reflection of same message in B→ a direction 復大辱软件学院 LiST
LiJT 18 Unilateral: Using timestamps • Time-Based Implicit Challenge • Alice ® Bob: EK(tA, B) • Bob decrypts and verified that timestamp is OK • Parameter B prevents reflection of same message in B ® A direction
aRy mutual: using random numbers Bob→>Ace:b Alice→>Bob:Ek(ra,「b,B) Alice Challenge Bob Bob→> Alice:Ek(a,rb Alice checks that ra, rb are the ones used earlier 19 復大辱软件学院 LiST
LiJT 19 mutual: using random numbers • Bob ® Alice: rb • Alice ® Bob: EK(ra, rb, B) – Alice Challenge Bob • Bob ® Alice: EK(ra, rb) • Alice checks that ra, rb are the ones used earlier