Study on enabling a cryptographic algorithm transition to 256bits
The present document aims to address key requirements for introducing support for 256-bit symmetric algorithms into the 5G System as well as the coexistence of 128-bit and 256-bit cryptographic algorithms. Considering findings and conclusions from preceding work, the following points should be addressed as part of the present document:
Studying key issues and candidate solutions concerning the negotiation (selection) of key sizes between UE and network, including:
- Potential risks and impacts to the current system when supporting both 128-bit and 256-bit algorithms in parallel and the adoption of 256-bit algorithms in existing deployments where 128 bits is already supported, e.g. handover scenarios within 5G system.
- How to prioritise the use of 256-bit algorithms and mitigate bidding-down attacks when negotiating key sizes.
- How to ensure 256-bit security is achieved concerning varying levels of support for 256-bit algorithms by different UEs and within the network; potential dependencies in key-length selection of AS and NAS layers.
- Study the implications and requirements for the key hierarchies to support 256-bit cryptographic algorithms.
- Study the implications and requirements to AKA procedures.