We design differentially private algorithms for the problem of online linear optimization in the fullpinformation and bandit settings with optimal regret bounds. In the full-information setting, our results demonstrate that "-different privacy may be ensured for free p – in particula the regret bounds scale as For bandit linear optimization, and as a special case for non-stochastic multi-armed bandits,?the prop posed algorithm achieves a regret of while the previously known best regret bound was