On the Security of E-Passports
by Marc Witteman - CTO of Riscure - Monday, 3 December 2007.
Active Authentication

The cloning problem is addressed with an optional signing mechanism called active authentication. This method requires the presence of a asymmetric key-pair and public key cryptographic capabilities in the chip. The public key, signed by the issuing country and verified by passive authentication, can be given to the inspection system, which allows verification of a dynamic challenge signed with the private key. While the private key is well protected by the chip it effectively prevents cloning since the inspection system can establish the authenticity of the passport chip with the active authentication mechanism.


For the incorporation of modern electronic technology in the existing paper documents it was decided to use (contactless) RFID chips. These chips can be embedded in a page of the document and put no additional requirements on the physical appearance of the passport. A question that arises here is whether this is the only reason to apply RFIDs instead of contact based cards. Other reasons could be related to the form factor of contact smart cards which complicates embedding in a passport booklet, or the fact that contacts may be disturbance sensitive due to travel conditions. With the choice for RFID the privacy issue arises. RFIDs can be accessed from distances up to 30 cm, and the radio waves between a terminal and an RFID can be eavesdropped from a few meters distance. An adversary with dedicated radio equipment can retrieve personal data without the passport owner’s consent. This risk is particularly notable in a hostile world where terrorists want to select victims based upon their nationality, or criminals commit identity theft for a variety of reasons.

Figure 2: Radio communication between inspection system and passport.

Basic Access Control

To protect passport holder privacy the optional Basic Access Control (BAC) mechanism was designed. This mechanism requires an inspection system to use symmetric encryption on the radio interface. The key for this encryption is static and derived from three primary properties of the passport data: 1) date of birth of holder; 2) expiry date of the passport; 3) the passport number. This data is printed in the Machine Readable Zone (MRZ) a bottom strip (see figure Figure 3) of one of the passport pages. In a normal access procedure the MRZ data is read first with an OCR scanner. The inspection system derives the access key from the MRZ data and can then set up an encrypted radio communication channel with the chip to read out all confidential data. Although this procedure can be automated it sets high requirements to inspection systems and also impacts inspection performance.

Figure 3: Passport with Machine Readable Zone (MRZ).


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