As every researcher will tell you, the most basic rule of cryptography definded by one of Kerckhoffs' principle is: NO SECURITY THROUGH OBSCURITY i.e. the security of the system should not be dependant on the secrecy of the emplyed algorithms, but only on the secrecy of the keys. Sadly, as it stands, i cannot ascertain whether or not this is the case for BTSync. Wherever this cannot be ascertained, one may assume one of two things a possibility as follow. hidden implementations point to weak, i.e. arbitrarily secure systems presence of "backdoors" A reminder on the basic levels of security by descending order of security: unconditionally secureconditionally securevery well reviewedbarely reviewedsecret You don't have to release it under Open Source, but at least make review possible!