Symmetric Key Crypto Notes

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Mutual Authentication - Long

Msg1 A → B : I’m Alice

Msg2 B → A : R1

Msg3 A → B : {R1}KAB

Msg4 A → B : R2

Msg5 B → A : {R2}KAB

Short

Msg1 A → B : I’m Alice, R2

Msg2 B → A : R1, {R2}KAB

Msg3 A → B : {R1}KAB

Reflection Attack

Msgα.1 A[E] → B : I’m Alice, R2 //Run α of the protocol

Msgα.2 B → A[E] : R1, {R2}KAB

//stops run because can't continue. starts run β

Msgβ.1 A[E] → B : I’m Alice, R1

Msgβ.2 B → A[E] : R3, {R1}KAB

//tricks bob into giving {R1}KAB

Msgα.3 A[E] → B : {R1}KAB

//Eve can now supply the 3rd message {R1}KAB of the short

//protocol above

Symmetric Key Crypto