SoK: On the Security & Privacy in Federated Learning

Advances in Machine Learning (ML) and its wide range of applications boosted its popularity. Recent privacy awareness initiatives as the EU General Data Protection Regulation (GDPR) - European Parliament and Council Regulation No 2016/679, subdued ML to privacy and security assessments. Federated Learning (FL) grants a privacy-driven, decentralized training scheme that improves ML models' security. The industry's fast-growing adaptation and security evaluations of FL technology exposed various vulnerabilities. Depending on the FL phase, i.e., training or inference, the adversarial actor capabilities, and the attack type threaten FL's confidentiality, integrity, or availability (CIA). Therefore, the researchers apply the knowledge from distinct domains as countermeasures, like cryptography and statistics. This work assesses the CIA of FL by reviewing the state-of-the-art (SoTA) for creating a threat model that embraces the attack's surface, adversarial actors, capabilities, and goals. We propose the first unifying taxonomy for attacks and defenses by applying this model. Additionally, we provide critical insights extracted by applying the suggested novel taxonomies to the SoTA, yielding promising future research directions.