Patent Document

RELATED APPLICATION 
       [0001]    This application claims benefit and priority to U.S. Provisional Patent Application Ser. No. 60/908,999, filed Mar. 30, 2007, the disclosure of which is incorporated by reference herein. 
     
    
     BACKGROUND 
       [0002]    A tag reader in an radio frequency identification (RFID) system uses an antenna to send radio frequency (RF) signals to an RFID tag. In response to the RF signals from the reader antenna, the RFID tag produces a disturbance in the magnetic (or electric) field that is detected by the reader antenna when a particular tag is within the detection range of the reader. 
         [0003]    The detection range of the RFID systems is typically limited by signal strength to short ranges. An HF RFID tag is typically more expensive than a typical UHF tag, and an HF tag generally has a comparatively shorter operational range. Conversely, a UHF RFID tag is typically less expensive than a typical HF tag and supports longer-range communications. HF RFID tags generally provide more stringent security features than UHF tags, which may provide little or no security with respect to access to information stored on a tag or with respect to cloning or forging of tag credentials. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]      FIG. 1A  shows an exemplary system for cryptographically combining two electronic credentials, such as a UHF RFID tag and an HF RFID tag/smart card to create a single multi-use credential or ‘enhanced’ RFID tag; 
           [0005]      FIG. 1B  shows an exemplary variant of the present method, which combines a UHF RFID tag with a contact smart card or a combination contact/contactless smart card to create an enhanced RFID tag; 
           [0006]      FIG. 2  is a flowchart showing an exemplary method for cryptographically linking a non-secure UHF RFID tag to a secure HF RFID tag; and 
           [0007]      FIG. 3  is a flowchart showing an exemplary method for using an enhanced tag  100  as a component in a security system. 
       
    
    
     DETAILED DESCRIPTION 
       [0008]      FIG. 1A  shows an exemplary system for cryptographically combining two electronic credentials, such as a UHF RFID tag  102  and an HF RFID tag/smart card  101  to create a single multi-use credential or ‘enhanced’ RFID tag  100 (A). The present system employs a method for cryptographically linking a non-secure UHF RFID tag  102  to a secure HF RFID tag  101  such that, in combination, the resulting ‘enhanced’ tag  100  provides the benefits of both tag types while ameliorating disadvantages of both. In an exemplary embodiment, the enhanced tag is included in a single tamper-proof piece of physical media, to protect against physical tampering. 
         [0009]      FIG. 1B  shows an exemplary variant of the present method, which combines a UHF RFID tag  102  with a contact smart card  105  (ISO7816, for example) or a combination contact/contactless smart card  105  (ISO7816+ISO14443, for example) to create an enhanced RFID tag  100 (B). In both tags  100 (A) and  100 (B), the UHF tag  102  may be optionally coupled to the second (the HF) tag  101  or to smart card  105  via shared memory  107 . Hereinafter, references to “HF tags”  101  are also applicable to “smart cards”  105 . Alternatively, the HF tag  101  may be a magnetic stripe—the UHF tag is used most of the time, and occasionally the user is required to swipe the magnetic stripe to reconfirm the validity of the UHF tag. 
         [0010]    In an exemplary embodiment, the two types of tags (UHF tag  102  and the second tag/card type  101 / 105 ) are proximately co-located (i.e., within approximately 2 cm or less of each other, or within a distance not greater than the range of the HF tag) in the same container or packaging unit, such as an ISO hard card or standard credit card, which provides enhanced protection against ‘tearing’ attacks where one of the credentials is separated and replaced. In the present system, the linkage between the UHF tag  102  and the HF tag  101 / 105  is cryptographic, in the form of a digital signature. This is equivalent to linking a relatively secure credential, e.g., a passport, to another, weaker credential, e.g., an employee badge. In the present analogy, the badge, typically used on a regular basis (e.g., daily), is backed up by the passport (and cryptographically linked to it) so that the badge ID can be periodically confirmed by the valid passport that was used to validate the badge holder&#39;s identity in the first place. 
         [0011]    This enhanced RFID tag  100  allows new and enhanced uses for RFID applications including:
       (1) using the HF tag  101  to prevent cloning of unsecured UHF tags used for consumables;   (2) using UHF tag  102  for asset/person tracking with occasional HF identity verifications to confirm the identity of the asset being tracked; and   (3) using the dual tag in a Kerberos- or SAML-like mode where the HF tag  101  is the long lived credential (which is protected by its short range of use and security features) and the UHF tag  102  is the Kerberos ticket or SAML name assertion equivalent. This allows the UHF tag  101  to be used for access at significant range (which additionally allows for ease of use, such as with wheelchair door access). The HF tag  101  can be used as an extension of the trust base (e.g., a Kerberos server), allowing many transactions to be completed offline without the need to do a live lookup to a trust system for every transaction. The present method significantly extends the utility of systems like Liberty/SAML and Kerberos, which are otherwise designed to always perform online trust verification.       
 
         [0015]    Given a UHF tag  102  and an HF tag  101 , where it is more likely (although not required), that the HF tag has more processing capabilities, on many occasions it may be possible to access the UHF tag but not the HF tag (due to the distance between the enhanced tag and the reader, for example). The present method authenticates the UHF tag  102  and binds it to a specific HF tag  101 . The present method also provides partial protection against cloning of the UHF tag and privacy for the carrier of the UHF tag. 
         [0016]      FIG. 2  is a flowchart showing an exemplary method for cryptographically linking a non-secure UHF RFID tag  102  to a secure HF RFID tag  101 . The cryptographic linkage of the UHF tag  102  to the HF tag  101  is performed as follows (in all cases, the HF tag may be replaced by a contact smart card or combination contact and contactless smart card), as shown in  FIG. 2 . Initially, at step  205 , signed and optionally encrypted data is stored on the UHF tag  102 . In an exemplary embodiment, a nonce (a number used only once) is included in the signed data. The tag signature may be a symmetric signature (e.g. full or truncated HMAC) or an asymmetric signature (e.g. ECDSA, RSA or DSA). The signer may be the HF tag itself, third party trusted authority, or both. The signed data may include the HF tag&#39;s public ID, HF tag&#39;s private ID, HF tag&#39;s public key, UHF tag&#39;s physical characteristics (e.g. non-linear characteristics used as a hardware fingerprint, specific response timings or other physical based characteristics), an external unique ID, bearer/item characteristics, a nonce, timestamp and application-specific data. 
         [0017]    At step  210 , if the data on the UHF tag  102  is encrypted, it may be encrypted with a key derived from any or all of the anticollision ID, physical characteristics, and bearer/item characteristics. At step  212 , if the data is encrypted it may be re-encrypted with a different IV (initial vector) or anticollision ID at each read to provide additional privacy by effectively changing the visible contents of the tag, even if the encrypted contents remain largely or entirely the same. Alternatively, the UHF tag  102  may be re-encrypted according to a policy, for example, once per day, or by way of a policy requiring interaction with the HF tag part of the enhanced tag  100  once per day according to whether the timestamp for the UHF tag has been updated to the current day. 
         [0018]    UHF tag events may be authenticated at read time or in batch mode at the next HF tag-RFID reader interaction. Protection against cloning and rollback may be enhanced by updating the nonce, at step  215 . In the case of a symmetric key solution this nonce can be updated by a reader and stored in a database at a given authority (which may transferred to another authority over time by an authority to authority protocol). In the case of an asymmetric key solution, the same can be done, or the nonce update can be deferred to the next time both HF and UHF tags  101 / 102  are read together. 
         [0019]    In the case where the signer is the HF tag  101  it may be the case that the HF tag is either a smart card, a simple memory card, or a memory card with limited cryptographic capabilities (e.g., DESFire, CryptoRF). In the latter two cases where the HF tag  101  is a memory card, the card may contain the symmetric or asymmetric private key which is used by reader but not retained by the reader. Alternatively, it may be the case that the HF tag&#39;s private key is derived from a master key plus attributes of, and data stored on, the HF tag. As indicated at step  220 , the contents of HF tag  101  may be encrypted, require authentication for access thereto, be transferred with transport protection, or any combination of such options. 
         [0020]    The above-described method may be combined with sequence numbers and authoritative transfers. The latter case includes the use of anticloning UHF transactions between HF verifications then tracking UHF (while maintaining privacy) between HF verifications. 
         [0021]    Sequence numbers are used to foil replay attacks. A tag having sequence number N indicates that the tag has had N uses, and the consumer of the ticket checks that number against what it expects the next sequence number to be. Thus, for example, if it is expected that there are 10 uses left (e.g., sequence number 90 out of 100), and a particular tag has a sequence number 10 of 100, then either the tag was legally recharged or a replay attack is being attempted. 
         [0022]    An authoritative transfer occurs when the owner of the ticket is legitimately changed (which is otherwise, always considered to be an attack). This technique is typically employed by a trusted third party overseeing the transfer. 
         [0023]    With or without additional anticloning protections, the present dual-tag method may be used with risk management routines to perform a Kerberos style single sign-on or transfer of high value credentials to long value credentials for limited duration. Kerberos is a computer network authentication protocol which allows individuals communicating over a non-secure network to prove their identity to one another in a secure manner. Kerberos builds on symmetric key cryptography and requires a trusted third party. Kerberos uses as its basis the Needham-Schroeder protocol, which makes use of a trusted third party, termed a key distribution center (KDC), which consists of two logically separate parts: an Authentication Server (AS) and a Ticket Granting Server (TGS). Kerberos works on the basis of ‘tickets’ which serve to prove the identity of users. The KDC maintains a database of secret keys; each entity on the network—whether a client or a server—shares a secret key known only to itself and to the KDC. Knowledge of this key serves to prove an entity&#39;s identity. For communication between two entities, the KDC generates a session key which they can use to secure their interactions. 
         [0024]    An analogy to Kerberos may be drawn in the present system, where a high value credential (e.g., a Ticket Granting Ticket or TGT) is used to obtain access to a service ticket that is essentially a signed (technically, an encrypted) service entitlement. That entitlement is then presented repeatedly until it expires. This process may be viewed as being similar to the HF tag corresponding to the TGT while the UHF tag stores the signed service entitlements. 
         [0025]    In the above case the HF tag  101  has two roles: both the TGT and the actual Kerberos server itself. Purely offline transactions may be supported with the majority of the risk management state and logic being stored (but not necessarily processed) on the HF tag  101 . Offline transactions may be considered as transactions not requiring immediate access to an authorization/authentication server such as a Kerberos server, but relying on such an interaction having occurred some time in the past and occurring again at some point in the future. Thus, as long as the HF tag  101  is valid, it may issue the service entitlements according to policy stored in it. The HF tag  101  may also act more like a TGT in the sense that it may require that it be unlocked only periodically with a high value credential such as a fingerprint, pin or attendant verified photo. 
         [0026]      FIG. 3  is a flowchart showing an exemplary method for using an enhanced tag  100  as a component in a security system, wherein the HF tag  101  corresponds to a high-value credential (e.g., TGT), and contains rules including the TGT and Kerberos server rules, while the UHF tag  102  stores the signed service entitlements. As shown in  FIG. 3 , at step  305 , the enhanced tag  100  is used to perform a Kerberos-style single sign-on or transfer of high value credentials to long value credentials for a limited duration. At step  310 , HF tag  101  uses a high value credential (e.g., TGT) to obtain a service ticket that is an encrypted service entitlement. 
         [0027]    At step  315 , the entitlement is presented to one or more readers repeatedly until the entitlement expires. While the HF tag  101  is valid, it issues the service entitlements according to policy stored therein. Offline transactions are supported with risk management state and logic being stored on the HF tag. The HF tag may optionally permit its being unlocked only periodically using a high value credential such as a fingerprint, a PIN, and an attendant-verified photograph, as indicated at step  320 . 
         [0028]    ‘Tips’ to help include risk management in the service entitlements may be included in the present system, for example, statements tied to the UHF part of the enhanced card  100 , such as whether the holder is an adult or child. In addition, risk management rules may also be included, such as determining if a particular procedure is performed more than N times, and if so, then revoking this service entitlement. 
         [0029]    The present system may also be employed in a scenario where there is more than one service to be unlocked and service access to the UHF portion of the enhanced card  100  is allowed instead of tag tracking only. One example of an application for the present system is access control where there are a number of automatic doors to different parts of facility, such as in a hospital. The hospital may divide different departments into different services and require that they authenticate with their HF tag once every given amount of time, but otherwise use UHF to allow individuals to enter a door, or detect whether there is more than one person present at the door. For some high value doors, an HF swipe may still be required [rather than dual factor (HF and UHF) swipes] except once a day, or after some inactivity timeout. Hospital employees, for example, may also be required to use a fingerprint or PIN. Then, fast free access would still be allowed, while maintaining reasonable security, and also maintaining an audit of employee movements (for the purpose of tracking down drug theft, for example). 
         [0030]    While preferred embodiments of the disclosed subject matter have been described, so as to enable one of skill in the art to practice this subject matter, the preceding description is intended to be exemplary only, and should not be used to limit the scope of the disclosure, which should be determined by reference to the following claims.

Technology Category: 5