Related:

• If you would keep a secret from an enemy, tell it not to a friend.
• If you would keep your secret from an enemy, tell it not to a friend. -- Ben Frankli
• If you want someone to keep a secret, keep it yourself.
• Your enemy is never a villain in his own eyes. Keep this in mind
  it may offer a way to make him your friend. If not, you can kill him without hate - and quickly....
• Tell nothing to thy friend that thy enemy may not know. Danish Proverb
• I shall tell you a great secret, my friend. Do not wait for the last judgment, it takes place every day.
  -- Albert Camu...
• If you had an off switch, doctor, would you not keep it a secret?
  I guess I would. -- Data and Dr. Crusher, "Datalore", stardate 41242.4...
• Of course the whole point of the Dooms Day Machine is lost if you keep it a secret!
  Why didn't you tell the world?? -- Dr. Strangelove...