Nowadays cryptography has been used to increase trust in confidentiality of many sources of information. Indeed, such technologies are helpful in protecting data from illegal accesses, yet drawbacks arise if they have to be enforced by investigative authorities to collect evidence. Balancing investigative powers and fundamental rights - most importantly, privacy - is difficult, especially when decryption keys are provided by human fingerprints or other biological traits. In this paper we focus on Digital forensics of encrypted mobile devices in the EU legal framework.