Schedule B - Constitution Act, 1982 (79)
PART I - Canadian charter of rights and freedoms
Legal Rights
11. Any person charged with an offence has the right
...
g) not to be found guilty on account of any act or omission unless, at the time of the act or omission, it constituted an offence under Canadian or international law or was criminal according to the general principles of law recognized by the community of nations;
Non-retroactivity
Nullum crimen sine lege
EDIT.