Power analysis is a very successful cryptanalytic technique which extracts secret information from smart cards by analysing the power consumed during the execution of their internal programs. It is a passive attack in the sense that it can be applied in an undetectable way during normal interaction with the smart card without modifying the card or the protocol in any way. The attack is particularly dangerous in financial applications such as ATM cards, credit cards, and electronic wallets, in which users have to insert their cards into card readers which are owned and operated by potentially dishonest entities. In this paper we describe a new solution to the problem, which com- pletely decorrelates the external power supplied to the card from the internal power consumed by the chip. The new technique is very easy to implement, costs only a few cents per card, and provides perfect protec- tion from passive power analysis.