Activate Later Certificates for V2X - Combining ITS efficiency with privacy
We specify Issue First Activate Later (IFAL). This is an ETSI [11] type of V2X Public Key Infrastructure based on short-lived pseudonymous certificates without Certificate Revocation Lists. IFAL certificates are valid in the future but can only be used together with periodically provided activation codes. IFAL supports controlled de-pseudonymization enabling provisioning to stop for misbehaving vehicles. IFAL allows for flexible policies, trade-offs between three essential V2X properties: trust, privacy and usability. IFAL activation codes are small and can be sent in an SMS, through roadside equipment or even broadcasted. Like the Butterfly scheme [32], IFAL uses key derivation with one base private/public key pair. However in IFAL the security module can be simple as it can be kept oblivious of key derivation.