Speed of inspection is a major hurdle to realising return on investment for ePassport technology. Put simply, if an ePassport cannot be read quickly, it will not be read at all. Hitech electronic and physical security features count for nothing if they cannot be properly and regularly examined, and manpower, technology and space constraints at border control mean that it is simply impractical for most nations to fully inspect every passport seen. However, there are new approaches to boosting inspection speed without compromising security: this paper introduces a technology which dramatically accelerates inspection in the average case by eliminating the bulk data transfer phase from the smartcard communication entirely.
The proposed solution is an encrypted caching mechanism, which caches the bulk data (data groups 1—16), bypassing the need to transfer this data over the low-speed smartcard communication link. Such a cache is typically pre-loaded with the biometric data of the deploying nation's ID holders, and rapidly accumulates cached data on all international travellers (or a chosen subset of travellers, whatever is preferred) on their initial visits. Using this technology, typical Basic Access Control (BAC) electronic passports can be read almost instantaneously (<1 second), regardless of the amount of data stored. It is particularly well suited for high throughput border control scenarios such as international airports, where speed of inspection is critical. There is no dependence on specific chip stock type, and the technique can be applied to documents already in the field.
Of course, the challenges to realising such an encrypted cache system are both technical and legal. For instance, if such a cache was encrypted with a key held by each inspection system, the data would be subject to abuse, and would likely fall foul of both data protection legislation, and EU regulations on usage of biometric data retrieved from EU ePassports. However, the scheme described uses a different encryption key for each cache entry, which exists only on the ePassport itself, thus the cache information is impossible to extract or abuse without possession of the physical document (which contains the same data anyway). Each cache entry exists in an essentially "deleted" state until the corresponding identity document becomes available again. Deletion of data by destroying the encrypting key is the same mechanism as is used by the Hardware Security Modules (HSMs) that store the cryptographic keys underlying the ePassport issuing PKI.
Individual cache keys are derived from high-entropy information within the Document Security Object (SOD) contained in an ePassport, and a pseudonymous storage and retrieval identifier is derived in the same way. Cache integrity is assured through the existing ID document integrity mechanisms of hashing and digital signatures, thus if any cache data is modified the inspection system retrieving the data will immediately become aware. Thus confidentiality, integrity and anonymity of the cache data are all assured. The paper further details an extension of the general method to address secure storage of EAC-protected data without violating the EAC terminal authentication security policy.
The paper describes various deployment scenarios for the encrypted cache, for example, the central server model where a port of entry data centre contains a LAN-accessible cache with 1—10TB of storage. As all of the cache data remains encrypted until reaching the inspection system, no additional network security or access control is required.