The United Kingdom (UK) government is considering advanced primitives such as identity-based encryption (IBE) for adoption as they transition their public-safety communications network from TETRA to an LTE-based service. However, the current LTE standard relies on elliptic-curve-based IBE, which will be vulnerable to quantum computing attacks, expected within the next 20-30 years. Lattices can provide quantumsafe alternatives for IBE. These schemes have shown promising results in terms of practicality. To date, several IBE schemes over lattices have been proposed, but there has been little in the way of practical evaluation. This paper provides the first complete optimised practical implementation and benchmarking of LATTE, a promising Hierarchical IBE (HIBE) scheme proposed by the UK National Cyber Security Centre (NCSC) in 2017 and endorsed by European Telecommunications Standards Institute (ETSI). We propose optimisations for the KeyGen, Delegate, Extract and Gaussian sampling components of LATTE, to increase attack costs, reduce decryption key lengths by 2x-3x, ciphertext sizes by up to 33%, and improve speed. In addition, we conduct a precision analysis, bounding the Rényi divergence of the distribution of the real Gaussian sampling procedures from the ideal distribution in corroboration of our claimed security levels. Our resulting implementation of the Delegate function takes 0.4 seconds at 80-bit security level on a desktop machine at 4.2GHz, significantly faster than the order of minutes estimated in the ETSI technical report. Furthermore, our optimised LATTE Encrypt/Decrypt implementation reaches speeds up to 9.7x faster than the ETSI implementation.Index Terms-lattice-based cryptography, hierarchical identity-based encryption, advanced primitives, software design, post-quantum
I. INTRODUCTIONT HE UK Government anticipates the migration of its mission-critical communications network from Airwave TETRA to LTE-based Emergency Services Network (ESN) [1] will be complete by 2026 [2]. However, the current standard [3] relies on Elliptic Curve (ECC)-based IBE scheme MIKEY-SAKKE for securing messages. The first such device authorised for ESN is the Panasonic Toughbook Tablet which runs on Intel i5 and transmits data via EM7511 Band 14 mobile broadband. An IBE scheme removes the need for a certificate repository by deriving a user's public key from their already established public identity. This provides a low latency setup with instantaneous communication capabilities, hence is ideal for this use-case. However, ECC will be rendered insecure under quantum computing attacks, as acknowledged by