A security expert has cracked one of the U.K.'s new biometric passports, which the British government hopes will cut down on cross-border crime and illegal immigration.

The attack, which uses a common RFID (radio frequency identification) reader and customized code, siphoned data off an RFID chip from a passport in a sealed envelope, said Adam Laurie, a security consultant who has worked with RFID and Bluetooth technology. The attack would be invisible to victims, he said.

"That's the really scary thing," said Laurie, whose work was detailed in the Sunday edition of the Daily Mail newspaper. "There's no evidence of tampering. They're not going to report something has happened because they don't know."

The British government, which began issuing RFID passports about a year ago, eventually wants to incorporate fingerprints and other biometric data on the chips, although privacy activists are concerned over how data will be stored and handled.

Currently, the chip contains the printed details on the passports, the person's photograph and security technology to detect if those files have been altered.

The attack was executed while the passport was still in its original envelope used to send it from the passport service, since RFID chips can be read from a few inches away, Laurie said. He used a passport ordered by a woman affiliated with No2ID, a group that opposes the U.K.'s biometric passport and ID card programs.

The data on the passport's chip is locked until an RFID reader provides the encryption key, Laurie said. The encryption key is calculated using a combination of the person's personal data, such as date of birth, and is contained in the "machine-readable zone" (MZR) -- the string of characters and digits on the bottom of the passport's first page.

At an immigration desk, the optical character reader scans the MZR and gets the key. The RFID chip is unlocked, and the information on the chip is matched with that on the passport.

However, Laurie was able to do this process himself. He analyzed ICAO 9303, the standard from the International Civil Aviation Organization that been adopted worldwide for machine-readable passports, to see how the MZR is organized.

Laurie also knew some of the woman's personal details -- used to calculate her passport's key -- and found out more through Internet research.

He then wrote what's known as a "brute force" program, which repeatedly tries different combinations of data to discover the key. After about 40,000 attempts by the program, he cracked the key.

To scan the chip, he used a common RFID reader from ACG ID, now part of Assa Abloy Identification Technology GmbH of Germany.

The attack could then let Laurie begin the process of making an exact copy of the woman's passport. However, the U.K. Home Office defended the passports on Tuesday, asserting the hack doesn't make them less secure.

"The key point ... is that the information on the chip cannot by changed, rendering the procedure described by Adam Laurie pretty pointless," wrote Peter Wilson, senior press officer, in an e-mail.

Further, a cloned chip would have to be inserted into a forged passport, and new security measures in the passports make that "virtually impossible," the Home Office said, quoting a report released last month by the National Audit Office.

But Laurie said the new passports were marketed as enhancing security, "but so far I don't see anything about it that increases my security."

The greatest weakness with the passports is using relatively easy-to-find data to compose the encrypted key, Laurie said. It would be better to include more random elements that would render brute-force style programs nearly useless, he said.

Laurie's work spawned from concern over how users can know what's on their passport's chip.

"At the moment, if you want to see what's in your own passport, you have to go to passport office," Laurie said. "With my code, you can do it at home."

Laurie has published a library of open-source tools written in the Python programming language that will run on RFID readers made by ACG and by Frosch Electronics OEG, based in Austria.