Related to the aforementioned progresses, we introduced several novel methodologies that advance the state of the art in cryptographic design and evaluation, particularly in the context of physical security and post-quantum cryptography. We outline them next.
A key methodological innovation is the concept of levelled implementations that had been applied in symmetric cryptography in the past. It allows different parts of a cryptographic primitive to be protected with countermeasures of varying cost and strength. This approach was extended from symmetric to asymmetric designs, enabling more efficient and tailored protection strategies.
Another major contribution is the development of hard physical learning problems (e.g. Learning With Physical Rounding), which offer a new paradigm for building cryptographic primitives that inherently resist side-channel attacks. These methodologies bridge physical leakage models with mathematical hardness assumptions, opening new directions for secure design. Results on this topic is still in an early stage, but we expect reductions to standard problems by the end of the project.
In the domain of evaluation, we introduced the Training Information (TI) metric, which provides a fast-converging and reliable bound on the information leakage of an implementation. This metric supports extrapolation from small datasets and enables sound security claims even in constrained evaluation settings. It complements traditional metrics like Mutual Information and Perceived Information and has been validated both theoretically and empirically.
As for inter-disciplinary Developments, BRIDGE operates at the intersection of cryptography, hardware design, statistical learning, and formal verification. The project has leveraged techniques from machine learning (e.g. convergence analysis of profiling models), signal processing (e.g. leakage modelling), and microelectronics (e.g. hardware implementations) to inform cryptographic design. The project also explored connections with privacy-preserving technologies through a contribution on leakage-resilient garbled circuits.
Regarding knowledge and technology transfer finally, BRIDGE has primarily contributed to the broader cryptographic ecosystem through publications and collaborations with academic and industrial partners. Despite not yet completed, it is expected that several implementations developed during the project will be released as open-source prototypes and maintained through the SIMPLE-Crypto association (
https://www.simple-crypto.org(se abrirá en una nueva ventana)). This initiative will ensure long-term accessibility and usability of the project's outputs.
