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A biometric passport (also known as an e-passport or a digital passport) is a traditional passport that has an embedded electronic microprocessor chip which contains biometric information that can be used to authenticate the identity of the passport holder. It uses contactless smart card technology, including a microprocessor chip (computer chip) and antenna (for both power to the chip and communication) embedded in the front or back cover, or centre page, of the passport. The passport's critical information is printed on the data page of the passport, repeated on the machine readable lines and stored in the chip. Public key infrastructure (PKI) is used to authenticate the data stored electronically in the passport chip, making it expensive and difficult to forge when all security mechanisms are fully and correctly implemented.

Many countries are moving towards issuing biometric passports to their citizens. Malaysia was the first country to issue biometric passports in 1998. In December 2008, 60 countries were issuing such passports, which increased to over 150 by mid-2019.

The currently standardised biometrics used for this type of identification system are facial recognition, fingerprint recognition, and iris recognition. These were adopted after assessment of several different kinds of biometrics including retinal scan. Document and chip characteristics are documented in the International Civil Aviation Organization's (ICAO) Doc 9303 (ICAO 9303). The ICAO defines the biometric file formats and communication protocols to be used in passports. Only the digital image (usually in JPEG or JPEG 2000 format) of each biometric feature is actually stored in the chip. The comparison of biometric features is performed outside the passport chip by electronic border control systems (e-borders). To store biometric data on the contactless chip, it includes a minimum of 32 kilobytes of EEPROM storage memory, and runs on an interface in accordance with the ISO/IEC 14443 international standard, amongst others. These standards intend interoperability between different countries and different manufacturers of passport books.

Some national identity cards, such as those from the Netherlands, Albania and Brazil, are fully ICAO 9303 compliant biometric travel documents. However others, such as the United States Passport Card, are not.

Data protection

Biometric passports have protection mechanisms to avoid and/or detect attacks:
; Non-traceable chip characteristics: Random chip identifiers reply to each request with a different chip number. This prevents tracing of passport chips. Using random identification numbers is optional.
; Basic Access Control (BAC): BAC protects the communication channel between the chip and the reader by encrypting transmitted information. Before data can be read from a chip, the reader needs to provide a key which is derived from the Machine Readable Zone: the date of birth, the date of expiry and the document number. If BAC is used, an attacker cannot (easily) eavesdrop transferred information without knowing the correct key. Using BAC is optional.
; Passive Authentication (PA): PA is aimed at identifying modification of passport chip data. The chip contains a file, Document Security Object (SOD), that stores hash values of all files stored in the chip (picture, fingerprint, etc.) and a digital signature of these hashes. The digital signature is made using a document signing key which itself is signed by a country signing key. If a file in the chip (e.g., the picture) is changed, this can be detected since the hash value is incorrect. Readers need access to all used public country keys to check whether the digital signature is generated by a trusted country. Using PA is mandatory. According to a September 2011 United States Central Intelligence Agency document released by WikiLeaks in December 2014, "Although falsified e-passports will not have the correct digital signature, inspectors may not detect the fraud if the passports are from countries that do not participate in the International Civil Aviation Organization's Public Key Directory (ICAO PKD)." As of January 2017, 55 of over 60 e-passport-issuing countries belong to the PKD program.
; Active Authentication (AA): AA prevents cloning of passport chips. The chip contains a private key that cannot be read or copied, but its existence can easily be proven. Using AA is optional.
; Extended Access Control (EAC): EAC adds functionality to check the authenticity of both the chip (chip authentication) and the reader (terminal authentication). Furthermore, it uses stronger encryption than BAC. EAC is typically used to protect fingerprints and iris scans. Using EAC is optional. In the European Union, using EAC is mandatory for all documents issued starting 28 June 2009.
; Supplemental Access Control (SAC): SAC was introduced by ICAO in 2009 for addressing BAC weaknesses. It was introduced as a supplement to BAC (for keeping compatibility), but will replace it in the future.
; Shielding the chip: This prevents unauthorised reading. Some countries – including at least the US – have integrated a very thin metal mesh into the passport's cover to act as a shield when the passport cover is closed. The use of shielding is optional.

To assure interoperability and functionality of the security mechanisms listed above, ICAO and German Federal Office for Information Security (BSI) have specified several test cases. These test specifications are updated with every new protocol and are covering details starting from the paper used and ending in the chip that is included.

Attacks

Since the introduction of biometric passports, several attacks have been presented and demonstrated.

; Non-traceable chip characteristics
: In 2008 a Radboud/Lausitz University team demonstrated that it's possible to determine which country a passport chip is from without knowing the key required for reading it. The team fingerprinted error messages of passport chips from different countries. The resulting lookup table allows an attacker to determine from where a chip originated. In 2010 Tom Chothia and Vitaliy Smirnov documented an attack that allows an individual passport to be traced, by sending specific BAC authentication requests. In 2016 Avoine et al. published a survey on security and privacy issues in passport protocols, where a new technique to track passports is introduced, based on the response time of basic commands.
; Basic Access Control (BAC)
: In 2005 Marc Witteman showed that the document numbers of Dutch passports were predictable, allowing an attacker to guess/crack the key required for reading the chip. In 2006 Adam Laurie wrote software that tries all known passport keys within a given range, thus implementing one of Witteman's attacks. Using online flight booking sites, flight coupons and other public information it's possible to significantly reduce the number of possible keys. In some early biometric passports BAC wasn't used at all, allowing attacker to read the chip's content without providing a key.
; Passive Authentication (PA)
: In 2006 Lukas Grunwald demonstrated that it is trivial to copy passport data from a passport chip into a standard ISO/IEC 14443 smartcard using a standard contactless card interface and a simple file transfer tool. Grunwald used a passport that did not use Active Authentication (anti-cloning) and did not change the data held on the copied chip, thus keeping its cryptographic signature valid.
: In 2008 Jeroen van Beek demonstrated that not all passport inspection systems check the cryptographic signature of a passport chip. For his demonstration Van Beek altered chip information and signed it using his own document signing key of a non-existing country. This can only be detected by checking the country signing keys that are used to sign the document signing keys. To check country signing keys the ICAO PKD can be used. Only 5 out of 60+ countries are using this central database. Van Beek did not update the original passport chip: instead an ePassport emulator was used.
: Also in 2008, The Hacker's Choice implemented all attacks and published code to verify the results. The release included a video clip that demonstrated problems by using a forged Elvis Presley passport that is recognized as a valid US passport.
; Active Authentication (AA)
: In 2005 Marc Witteman showed that the secret Active Authentication key can be retrieved using power analysis. This may allow an attacker to clone passport chips that use the optional Active Authentication anti-cloning mechanism on chips – if the chip design is susceptible to this attack.
: In 2008 Jeroen van Beek demonstrated that optional security mechanisms can be disabled by removing their presence from the passport index file. This allows an attacker to remove – amongst others – anti-cloning mechanisms (Active Authentication). The attack is documented in supplement 7 of Doc 9303 (R1-p1_v2_sIV_0006) and can be solved by patching inspection system software. Note that supplement 7 features vulnerable examples in the same document that – when implemented – result in a vulnerable inspection process.
: In 2014 Calderoni et al. show a procedure to bypass the security protocol that is commonly adopted to prove chip authenticity (Active Authentication) within first-generation electronic passports. The discussed breach is related to some metadata files (EF.COM, EF.SOD) and allows the attacker to conceal those data required by the inspection system during the protocol's execution. This breach may facilitate a malicious user in using fake documents cloned from original ones.

; Extended Access Control (EAC)
: In 2007 Lukas Grunwald presented an attack that can make EAC-enabled passport chips unusable. Grunwald states that if an EAC-key – required for reading fingerprints and updating certificates – is stolen or compromised, an attacker can upload a false certificate with an issue date far in the future. The affected chips block read access until the future date is reached.

Opposition

Privacy proponents in many countries question and protest the lack of information about exactly what the passports' chip will contain, and whether they affect civil liberties. The main problem they point out is that data on the passports can be transferred with wireless RFID technology, which can become a major vulnerability. Although this could allow ID-check computers to obtain a person's information without a physical connection, it may also allow anyone with the necessary equipment to perform the same task. If the personal information and passport numbers on the chip are not encrypted, the information might wind up in the wrong hands.

On 15 December 2006, the BBC
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