The Internet is increasingly used to disseminate unethical and illegal content. A grave concern is child sexual abuse material that is often disseminated via end-to-end-encrypted channels. Such encryption defeats network- and server-based scanning measures used by law enforcement. A trade-off is to enable confidential communications channels for users and scanning opportunities for law enforcement by employing perceptual-hashing-based targeted content scanning on user devices. This has generated intense discussions between policymakers, privacy advocates and child protection organizations. This chapter summarizes the current state of reserch in perceptual-hashing-based targeted content scanning with a focus on classical metrics such as false positives, false negatives and privacy aspects. Insights are provided into the most relevant perceptual hashing methods and an attack taxonomy for perceptual-hashing-based targeted content scanning is presented. The complexity in generating false negatives is evaluated and the feasibility of evading perceptual-hashing-based targeted content scanning is demonstrated.    «

The Internet is increasingly used to disseminate unethical and illegal content. A grave concern is child sexual abuse material that is often disseminated via end-to-end-encrypted channels. Such encryption defeats network- and server-based scanning measures used by law enforcement. A trade-off is to enable confidential communications channels for users and scanning opportunities for law enforcement by employing perceptual-hashing-based targeted content scanning on user devices. This has generated...    »