In modern networks, data often traverses many intermediate nodes, spanning different
organizations and administrative domains. Traditional routing algorithms are designed to
find the shortest or fastest path, but they do not consider whether the path is
trustworthy. In critical environments, this is no longer enough. We need routes that are
not only fast, but also safe. This is the essence of the Trusted Path Routing (TPR)
problem.
The Trusted Path Routing problem focuses on finding a path from a source to a
destination where every intermediate node or link meets a required level of
trustworthiness. Each node or link can be assigned a trust score, while links also have
traditional costs such as latency or bandwidth consumption. The goal is to find a path
that satisfies trust constraints while also optimizing network performance. Instead of
only asking “what is the fastest path?”, TPR asks “what is the safest fast path?”. Routing
through untrusted nodes can lead to data interception, route hijacking, or disruption of
service. Ensuring that data only passes through trusted elements is therefore essential
for building resilient communication systems.
However, solving the TPR problem is challenging. It is not a standard shortest path
problem; it is a constrained routing problem, and often NP-hard. Trust scores are an
additional dimension that cannot be combined trivially with cost metrics, and they can
change over time as nodes gain or lose reputation. In many cases, no single path exists
that is both highly trusted and highly efficient, forcing a trade-off. This is exactly where
multi-objective optimization becomes valuable.
Within the CASTOR project, we will tackle the Trusted Path Routing problem as a multi-
objective optimization challenge. Our goal is to design quantum-ispired algorithms
that can jointly consider trust and performance metrics (such as latency, reliability, or
resource cost) to select routes that offer the best possible compromise. This approach
will allow us to generate multiple Pareto-optimal routing options, giving operators the
flexibility to prioritize either security or efficiency depending on mission context. By
embedding these capabilities into CASTOR’s secure networking framework, we aim to
make routing not only faster, but fundamentally more trustworthy.
Trust has always been a foundation of human communication, and it is now becoming a
critical foundation for machine communication as well. By addressing the Trusted Path
Routing problem through multi-objective optimization, CASTOR will contribute to
building the next generation of secure and resilient network infrastructures.
