Whoever wishes to keep a secret must hide the fact that he possesses one.
- Van Goethe

The man who can keep a secret may be wise, but he is not half as wise as the man with no secrets to keep.
- Edgar Watson Huwe

How can we accept another to keep a secret if we have unable to keep it ourselves.
- De La Rochefoucauld

Three can keep a secret if two are dead.
- Benjamin Franklin

Tell your friend a lie and if he keeps it secret, then tell him the truth.
- Proverb (don't know if I like that one much)