PART II.
PROTECTION OF FUNDAMENTAL RIGHTS AND FREEDOMS
Provision to secure protection of law
10. (4.) No person shall be convicted of an offence on account of any act or omission that did not, at the time it took place, constitute such an offence and no penalty shall be imposed for an offence that is more severe in degree or description than the maximum penalty that might have been imposed for that offence at the time when it was committed.
Non-retroactivity
Nullum crimen sine lege
Nulla poena sine lege
EDIT.