Basic access control: Difference between revisions

Revision as of 11:14, 15 February 2010

Revision as of 05:01, 21 February 2010

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'''Basic Access Control''' (BAC) is a mechanism specified to ensure only authorized parties{{FactCitation needed|date=April 2009}} can wirelessly read personal information from [[passport]]s with an [[RFID]] chip. It uses data such as the passport number, date of birth and expiration date to negotiate a session key. This key can then be used to encrypt the communication between the passports chip and a reading device. This mechanism is intended to ensure that the owner of a passport can decide who can read the electronic contents of the passport. This mechanism was first introduced into the German passport on 1 November 2005 and is now also used in many other countries (e.g., [[United States passport]]s since August 2007[http://travel.state.gov/passport/eppt/eppt_2788.html#Eleven]).

== Inner workings ==

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There is a replay attack against the Basic Access Control protocol that allows an individual passport to be traced <ref>[http://www.theregister.co.uk/2010/01/26/epassport_rfid_weakness/ Defects in e-passports allow real-time tracking, The Register, Dan Goodin, 26th Jan 2010] </ref>,<ref>[http://www.cs.bham.ac.uk/~tpc/Papers/PassportTrace.pdf A Traceability Attack Against e-Passports, Tom Chothia and Vitaliy Smirnov, 14th International Conference on Financial Cryptography and Data Security 2010]</ref>. The attack is based on being able to distinguish a failed nonce check from a failed MAC check and works against passports with randomized unique identifiers and hard to guess keys.

The Basic Access Control mechanism has been criticized as offering too little protection from unauthorized interception. Researchers claim {{citationCitation needed|date=February 2010}} that because there are only limited numbers of passport issued, many theoretically possible passport numbers will not be in use in practice. The limited range of human age ranges further reduce the space of possibilities.

In other words, the data used as an encryption key has a low [[entropy]], meaning that guessing the session key is possible via a modest [[brute force attack]].