name: PGK
full_form: ProSe Group Key
context: A receiving UE would need to derive the PTK using the information in the bearer header and from this the PEK used to decrypt the data. When the PGKs are provided to the UE (either through initial provisioning or from the ProSe Key Management Function (see subclause 6.2.6.2.3)), they are provided with an Expiry Time. The Expiry Times of the PGK need to be set in such that the later PGK keys have longer expire time before they expire. When a PGK key expires in the sending UE and receiving UE, all related keys as PTK and PEK derived from the expired PGK are deleted. When protecting data that is to be sent, the UE uses the first of the PGKs that has not expired to derive the PTK etc. When receiving protected data the UE only uses a PGK that has not expired or the PGK that has most recently expired. All other PGK should be deleted. Editor's note: The validity of this key management for PS purposes needs to be confirmed.
description: The ProSe Group Key (PGK) is a security parameter used in Proximity Services (ProSe) to derive other keys, such as the Pairwise Transient Key (PTK) and the Pairwise Encryption Key (PEK), for encrypting and decrypting data. It has an associated Expiry Time, after which it expires and all related keys derived from it are deleted.
explanation: The PGK is classified as a Parameter because it is a critical network attribute used in the operation of ProSe key management, specifically for deriving other keys and having an expiry time that affects its usage.
section_title: 6.3.5.2.1	Security keys and their lifetimes
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