Usability of Display-Equipped RFID Tags for Security Purposes
Lecture Notes in Computer Science
The recent emergence of RFID tags capable of performing public key operations has enabled a number of new applications in commerce (e.g., RFIDenabled credit cards) and security (e.g., ePassports and access-control badges). While the use of public key cryptography in RFID tags mitigates many difficult security issues, certain important usability-related issues remain, particularly when RFID tags are used for financial transactions or for bearer identification. In this paper, we focus exclusively
... on techniques with user involvement for secure user-to-tag authentication, transaction verification, reader expiration and revocation checking, as well as association of RFID tags with other personal devices. Our approach is based on two factors: (1) recent advances in hardware and manufacturing have made it possible to mass-produce inexpensive passive displayequipped RFID tags, and (2) high-end RFID tags used in financial transactions or identification are usually attended by a human user (namely the owner). Our techniques rely on user involvement coupled with on-tag displays to achieve better security and privacy. Since user acceptance is a crucial factor in this context, we thoroughly evaluate the usability of all considered methods through comprehensive user studies and report on our findings. Even though they are powerful enough to perform sophisticated public key cryptographic operations, security and privacy issues remain when these tags are used as a means of payment or for owner/bearer identification. In this paper, we address four such issues: User-to-Tag Authentication: In many applications of RFID in electronic payment and in identification documents, authentication of the user to the tag before disclosing any information is necessary to prevent leaks of valuable or private information. Current systems require trust in readers for the purpose of authentication. For example, users must enter PINs into ATMs or Point-of-Sale (POS) terminals to authenticate themselves to the RFID tag embedded into their ATM or credit card. However, this leaves users vulnerable to attacks, since secret PINs are being disclosed to third party readers that are easy to hack and modify. Transaction Verification: RFID tags are commonly used as payment and transaction instruments (e.g., in credit, debit, ATM and voting cards). In such settings, a malicious reader can easily mislead the tag into signing or authorizing a transaction different from the one that is communicated to, or intended by, the user. This is possible because there is no direct channel from a tag to its user on regular RFID tags (i.e., no secure user interface), and the only information a user gets (e.g., a receipt, or an amount displayed on the cash register) is under the control of a potentially malicious reader. Thus, it seems impossible for a user to verify (in real time) transaction details, e.g., the amount or the currency. This problem becomes especially important with current electronic credit cards. Reader Revocation and Expiration: Any certificate-based Public Key Infrastructure (PKI) needs an effective expiration and revocation mechanism. In RFID systems, it intuitively concerns two entities, namely RFID tags and RFID readers. The former only becomes relevant if each tag has a "public key identity," and we claim that revocation of RFID tags is a non-issue since, once a tag identifies itself to a reader, the reader can use any current method for revocation status verification. In contrast, expiration and revocation of reader certificates constitutes a challenging problem in any public key-enabled RFID system. This is because RFID tags, being powerless passive devices, cannot maintain a clock. In other words, an RFID tag (on its own) has no means to verify whether a given certificate has expired or whether any revocation information is recent. Secure Pairing of RFID Tags: Current high-end RFID tags cannot establish a secure ad-hoc communication channel to another device, unless the latter is part of the same RFID infrastructure (i.e., an authorized reader). Establishing such a channel seems important as it would give tag owners the ability to manage their tags. Previously proposed secure device pairing solutions require an auxiliary communication channel to authenticate devices and establish a secure communication channel  ,  . Until recently, however, RFID tags lacked user interfaces and thus could not be paired with other devices. Novel display-equipped RFID tags open a new chapter in RFID security and give users more control over their tags. Using an NFC-capable personal device (such as a smart-phone), for instance, a user can change settings on a personal RFID tag.