/usr/share/boinc-dev/lib/crypt.h is in libboinc-app-dev 7.9.3+dfsg-5.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/boinc-dev/lib/../../../include/boinc/crypt.h
/usr/share/boinc-dev/lib/../../../include/boinc/crypt.h