Frank Moss, deputy assistant secretary for Passport Services at the US Department of State, says the first digital passports will be issued in the US by 26 October 2004. Moss announced details of the plans at the Smart Card Alliance Government Conference and Expo in Virginia last Tuesday.

The new passports will include an embedded microchip that stores a compressed image of its owner's face. These microchips will be designed to prevent tampering and each digital image will be cryptographically signed to guarantee its authenticity.

Not everyone is convinced that digital passports are a good idea. Civil liberties groups fear that the introduction of such international identity schemes could permit governments to monitor the activities of citizens in unprecedented detail.

But Moss says the US passports have been designed with these concerns in mind. "They will include no information other than that on the basic passport information page," Moss told New Scientist.

He adds that passport checkpoints will not forward information to centralised databases unless there is query over the passport's authenticity. The passport's digital signature could then be checked against the cryptographic master key to ensure its legitimacy.

Raising the bar

However, some technical experts also warn that such systems cannot guarantee complete security. "Never forget that everybody behind September 11 was using photo ID," says Richard Clayton, a hardware security expert at Cambridge University in the UK. "It will raise the bar considerably," he says, but will only identify known suspects or those with forged passports.

Security experts have also demonstrated that smart cards designed to be tamper-proof can be vulnerable to interference. In January 2001 Ross Anderson and Sergei Skorobogatov, also at Cambridge University, showed that data could be retrieved from a smart card's memory unit by focusing light from an ordinary camera flashgun on it and flipping individual bits.

European travellers may also soon be required to carry passports containing biometric information. In June 2003 the European Union agreed to spend 140 million euros on the development of an interoperable biometric system.

European passports are expected to carry both fingerprint and iris scan biometric data. Fingerprints and iris scans are much easier to cross-reference on computer than photographs, for which varying hairstyles and facial hair add complications. Cross-referencing could determine if someone were using multiple passports, for example.

No date has been set for the introduction of biometric European passports but European countries are likely to be under pressure to comply with US standards.