Secrecy is the badge of fraud. – Sir John Chadwick

To have found you is a dear happiness; and to be Apollos son is beyond all my hopes; but there is something I want to say to you alone. Come; this is a private matter between us two – anything you tell me shall be as secret as the grave. – Euripides

Tell your friend a lie. If he keeps it secret, then tell him the truth. – Proverb