What a surprise.
You have nothing to fear if you have nothing to hide.
The phrase - widely used in discussions of Internet security and uttered by Pius Thicknesse in Harry Potter and the Deathly Hallows - is most commonly attributed to Joseph Goebbels in 1933.
However, there is an earlier precedent. Upton Sinclair used an inverted version in 1918 in The Profits of Religion: An Essay in Economic Interpretation:
Not merely was my own mail opened, but the mail of all my relatives and friends—people residing in places as far apart as California and Florida. I recall the bland smile of a government official to whom I complained about this matter: ‘If you have nothing to hide you have nothing to fear.’