An AKE Protocol Based on Key Distribution

The STS protocol is an AKE protocol based on key agreement and public-key cryptography. We will now look at an AKE protocol based on key distribution and the use of symmetric cryptography. This protocol is a simplified version of one from ISO 9798-2. This protocol involves using a trusted third party (denoted by TTP).

Protocol description

The idea behind this AKE protocol is that Alice and Bob both trust the TTP. When Alice and Bob wish to establish a shared key $K_{AB}$, they will ask the TTP to generate one for them, which will then be securely distributed to them. The protocol involves the following assumptions:

• Alice has already established a long-term shared symmetric key $K_{AT}$ with the TTP.

• Bob has already established a long-term shared symmetric key $K_{BT}$ with the TTP.

• Alice and Bob are both capable of randomly generating nonces.