Computer networks underpin many aspects of our daily lives. Familiar servicessuch as digital payments, social networks, video streaming and messaging appswould not function without them. While the services we enjoy may seem stableon the surface, underneath the hood they are ever-changing: components arereplaced, networks are rebuilt and source code is rewritten. Similarly, thethreat posed by malicious actors is also in constant motion. What is consideredsecure today may not be secure tomorrow. This is especially true for softwarecomponents. Therefore, software security testing is necessary to ensure that aservice poses no risk to its operators nor its end-users.

A critical step in developing secure software is discovering previously unknownvulnerabilities. Fuzz testing, or fuzzing, is a state-of-the-art techniquefor preventing insecure software from being taken into production. One form offuzz testing that has received great interest in recent years is grey-boxfuzzing. Unfortunately, some systems are not well-suited for this type oftesting. Implementation aspects such as programming language, statefulness,network connectivity and source-code availability can make grey-box fuzzingdifficult. Consequently, not all types of vulnerabilities are discoverable withthis technique.

In this thesis, I investigate a different approach to fuzzing: black-boxfuzzing. As the name suggests, black-box fuzzing does not depend onimplementation details about the target system. While this allows for testinga wider range of systems, it also pays a price by sacrificing speed and testcoverage. However, if the black-box fuzzer can find vulnerabilities that agrey-box fuzzer cannot, it might be worth the price. The results I present inthis thesis show that by incorporating elements from reinforcement learning andweb crawling, black-box fuzzing can be used where grey-box fuzzing falls shortto discover previously unknown vulnerabilities in real-world networkingsoftware.

This licentiate thesis investigates how forestry-derived biomaterials can reduce the fossil bitumen content of asphalt binders while maintaining functional performance. It focuses on lignin as a bio-based extender and on tall oil products as complementary softening bio-additives in a bio-composite binder. The work is motivated by two practical uncertainties in the literature: the ambiguous functional role of lignin in bitumen (often described as modifier-like or filler-like) and how this role affects the stiffness–flexibility trade-off.

The thesis addresses these questions through a combined approach: a systematic literature review and a targeted binder-scale experimental programme. The review confirms that lignin enhances high-temperature stiffness, rutting resistance, and ageing resistance, but it also identifies critical gaps: inconsistent mechanistic interpretation of lignin’s role, a lack of performance-balancing strategies, and insufficient comparative benchmarks.

Guided by these gaps, the experimental study evaluates a 70/100 paving-grade bitumen extended with 15 wt% kraft lignin (KL) or hydrolysis lignin (HL), using a limestone filler mastic (LSM) as an inert reference. Crude tall oil (CTO) and tall oil pitch (TOP PN) were assessed as secondary additives (5 and 10 wt%) in the KL-extended binder. Chemical and thermal analyses using Fourier-transform infrared spectroscopy and thermogravimetric analysis confirmed physical blending and thermal stability up to 190 °C for all binders. Rheological characterisation using dynamic shear rheometer and multiple stress creep and recovery testing revealed a clear functional distinction: KL behaved in a filler-like manner, showing a complex modulus and stress sensitivity very similar to the LSM mastic. In contrast, HL exhibited a modifier-like character, with significantly higher elastic recovery and lower non-recoverable creep compliance. Tall oil products acted as effective bio-fluxes; a 5 wt% dosage provided an optimal balance, improving workability and low-temperature flexibility while largely preserving the enhanced rutting resistance from KL. In contrast, a 10 wt% dosage, particularly of CTO, caused excessive softening, increased stress sensitivity, and a marked loss of high-temperature performance.

Overall, the thesis proposes a function-based framework for bio-composite binder design, where lignin type and tall oil dosage are selected according to their demonstrated role in the binder matrix, rather than treated as generic bitumen substitutes.