How to clone a biometric passport while it's still in the bag | The Register: "The data in the chip is essentially a digital version of what is printed inside the passport itself. The printed data can be read if the passport is presented and opened, and the chip's security system attempts to duplicate this process. The chip data can be read wirelessly, but it is encrypted, with the key printed inside the passport. So in theory, although the chip can be read without the passport (or indeed the delivery envelope) being opened, the data is meaningless without the key.
But the key in this first generation of biometric passport is relatively easy to identify/crack. It is not random, but consists of passport number, the passport holder's date of birth and the passport expiry date. The Mail found it relatively easy to identify the holder's date of birth, while the expiry date is 10 years from the issue date, which for a newly-delivered passport would clearly fall within a few days. The passport number consists of a number of predictable elements, including an identifier for the issuing office, so effectively a significant part of the key can be reconstructed from the envelope and its address label."