Abstract:
A hardware-locked encrypted backup (HWLE-BU) that is locked to a single hardware device using the device&#39;s unique hardware identity, based on a Physically-Unclonable Function (PUF) or other suitable means providing a unique hardware identity. The HWLE-BU is bound to a specific hardware identity such that only the physical device that created the HWLE-BU can decrypt it, i.e., restoring HWLE-BU data requires utilizing the same physical hardware device in the decryption process.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional patent application Ser. No. 62/037,928 filed Aug. 15, 2014. 
     
    
     BACKGROUND 
       [0002]    Securely protecting computer backups of data continues to be an area full of security concerns. When created, backups typically need to be stored in a format that can be restored at an unknown later date. Many things can change in the computer environment during the period between backup and restore, such as: changing or updating of operating system, changing of hardware components (hard drives, motherboards, network cards, etc.), virtualization of systems, changing of user IDs and passwords, etc. The ever-changing environment makes it difficult to backup computer data in a way that can be restored at a later date. 
         [0003]    To avoid additional restore complications, many computer backups are created with no or limited security protection. Even if security is enabled, the IT administrators may have access to all the keys and therefore access to the data in a decrypted form. In the case of critical/classified protected data, IT administrators may not be authorized to access such data, and creating a useable system that protects the critical/classified data from IT administrator access becomes a difficult task. 
         [0004]    Classified and other secure environments also impose chain of custody, accounting, and policy restrictions. These restrictions can prohibit creating copies of critical data unless the critical data is destroyed from a transferring system or device upon transfer of a copy to a receiving system or device, making it difficult to robustly protect critical data for restoration. 
       SUMMARY 
       [0005]    The hardware-locked encrypted backup (HWLE-BU) is an encrypted backup that is locked to a single hardware device. The HWLE-BU is encrypted using the device&#39;s unique hardware identity, based on a Physically-Unclonable Function (PUF) or other means that provides a unique hardware identity and meets a system&#39;s required level of security. By cryptographically binding the HWLE-BU to a specific hardware identity, the only physical device that can decrypt the HWLE-BU is the exact hardware that it was created for. That is, the only way to decrypt and restore the HWLE-BU data is to have access to the exact physical hardware device and utilize it in the decryption process. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIGS. 1-9  are a sequence of system diagrams illustrating an embodiment of a method of transferring critical data from an origin to an endpoint through a series of (three) intermediaries A, B, and C, destroying critical data in the intermediaries as it is transferred through them, but utilizing hardware-locked encrypted backups, wherein: 
           [0007]      FIG. 1  depicts an initial state wherein only the origin possesses the critical data; 
           [0008]      FIG. 2  depicts the transfer of a copy of the critical data from the origin to intermediary A; 
           [0009]      FIG. 3  depicts the transfer of a copy of the critical data (and destruction) from intermediary A to intermediary B; 
           [0010]      FIG. 4  depicts the creation of a hardware-locked encrypted backup by intermediary B using its PUF B ; 
           [0011]      FIG. 5  depicts the transfer of a copy of intermediary B&#39;s hardware-locked encrypted backup back to intermediary A; 
           [0012]      FIG. 6  depicts the transfer of a copy of the critical data (and destruction) from intermediary B to intermediary C; 
           [0013]      FIG. 7  depicts the creation of a hardware-locked encrypted backup by intermediary C using its PUF C ; 
           [0014]      FIG. 8  depicts the transfer of a copy of intermediary C&#39;s hardware-locked encrypted backup back to intermediary B; and 
           [0015]      FIG. 9  depicts the transfer of a copy of the critical data (and destruction) from intermediary C to the endpoint. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0016]    An encrypted-backup device according to the invention includes a processor, a memory, information providing a unique hardware identity, and typically an external input and external output. Information is extracted from the device uniquely identifying its hardware using a suitable means, for example via a PUF constructed to ensure that a unique value/identity is made for each and every device produced. Methods for extracting a unique hardware device identity utilizing a PUF challenge-response pair are described in various publications including U.S. Patent Application Publication No. 20150134966 (“the &#39;966 Publication”); U.S. Pat. Nos. 8,468,186 to Yu, 8,811,615 to Yu et al., 8,756,438 to Devedas et al., 8,683,210 to Devedas et al., and 7,839,278 to Devedas et al.; Armknecht et al., “A formalization of the security features of physical functions,” Proceedings of the 2011 IEEE Symposium on Security and Privacy, ser. SP &#39;11. Washington, DC: IEEE Computer Society, pp. 397-412; Frikken et al., “Robust authentication using physically unclonable functions,” Information Security, ser. Lecture Notes in Computer Science, vol. 5735, pp. 262-277 (Springer Berlin Heidelberg, 2009); Gassend et al., “Silicon physical random functions,” Proceedings of the 9 th  ACM conference on Computer and communications security, ser. CCS &#39;02, pp. 148-60 (New York, ACM, 2002); Holcomb et al., “Initial sram state as a fingerprint and source of true random numbers for rfid tags,” Proceedings of the Conference on RFID Security (2007); Kumar et al., “Extended abstract: The butterfly puf protecting ip on every fpga,” Hardware- Oriented Security and Trust, HOST 2008, IEEE International Workshop, pp. 67-70; Rührmair et al., “Applications of high-capacity crossbar memories in cryptography,” IEEE Trans. Nanotechnol., vol. 10, no. 3, pp. 489-498 (May 2011); Rührmair et al., “Pufs in security protocols: Attack models and security evaluations,” 2013 IEEE Symposium on Security and Privacy, pp. 286-300 (2013); Suh et al., “Physical unclonable functions for device authentication and secret key generation,” Proceedings of the 44 th  annual Design Automation Conference, ser. DAC &#39;07, pp. 9-14 (New York, ACM, 2007), which are incorporated herein by reference in that regard (including for their disclosure of PUF design properties, formal theoretical models, design protocols, and definitions). A PUF response used to uniquely identify the specific hardware device may be derived from a raw PUF response to the challenge, such as by fuzzy extraction described in the &#39;966 Publication at ¶¶[0054]-0057] and [0086]-[0088]; Dodis et al., “Fuzzy extractors: How to generate strong keys from biometrics and other noisy data,” SIAM J. Comput., vol. 38, no. 1, pp. 97-139 (2008); and Juels et al., “A fuzzy commitment scheme,” Proceedings of the 6th ACM conference on Computer and communications security, ser. CCS &#39;99, pp. 28-36 (New York, ACM 1999). The device&#39;s PUF may preferably be a controlled PUF configured and arranged so as to preclude release of PUF response data outside the device. 
         [0017]    This hardware identity of the specific device is then used to generate a unique encryption key that is recoverable only by that device. Such an encryption key can comprise, or be generated from a seed comprising, the response of a PUF in the device to a given challenge. The data that is desired to be backed-up is next encrypted, using the encryption key directly in a symmetric encryption algorithm, or using it to derive an asymmetric key pair for an asymmetric encryption algorithm. 
         [0018]    To decrypt the HWLE-BU, the specific device used to create it must regenerate the encryption key, in the case of a PUF-based key by utilizing the same challenge to generate the PUF response (e.g., with fuzzy extraction applied to the raw PUF response) used to make the key. Since only the specific device used to make the HWLE-BU can recreate the encryption key and decrypt the data that was backed-up, and since the device&#39;s hardware identity never exists outside of that device, the encrypted data can be viewed as a “black object.” An object of this type can be treated as non-sensitive, including being stored (possibly in multiple copies, depending on applicable conditions and policies) on alternate media as a secure backup, and managed and distributed by IT administrators and others without risk of exposing the data encrypted therein. For example, the encrypted backup can be stored on a separate non-volatile memory within the device that made the backup, and/or may be transferred and stored externally to the device. 
         [0019]    The HWLE-BU can be advantageous in environments (e.g., high-security critical/classified) where policies may prevent multiple copies of critical data and require that the originating copy of critical data be securely erased upon transfer to another device. For example, where critical data (e.g., cryptographic keys for use in an end cryptographic unit or keyloader) is transferred through a multiple-step path from an origin device or system to an endpoint device or system, the requirement of secure erasure can carry the risk of losing critical data or at least a set-back in the transfer process if a failure (battery loss, etc.) occurs in the transfer path. For example, in a transfer process such as the one shown in  FIGS. 1-9 , wherein conditions or policies require destruction of critical data usable by an intermediary device or system upon its transfer of critical data to the next recipient (such that failure could require re-starting the transfer process, potentially including one or more parties sequentially having to go to a different location again and connect to the origin and other intermediaries to each other etc.), the data could be transferred using intermediary devices or systems having internal PUFs used to create hardware-locked encrypted backups; a backup could then be sent back to the prior intermediary device or system in case of failure. Thus, if intermediary B has a failure, it can go back to intermediary A (without intermediary A first having to go back to the Origin) and retrieve from it and decrypt HWLE-BU B  to regain the critical data and transfer it to intermediary C. Likewise, if intermediary C has a failure, it can go back to intermediary B (without intermediary A first having to go back to the Origin System and then intermediary B back to intermediary A) and retrieve from it and decrypt HWLE-BU C  to regain the critical data and transfer it to the Endpoint. Once the entire transfer process or at least the next step in the chain is successfully completed, the backups may be destroyed. Further variations and adaptations can be employed depending on the system and policies; for example, in the foregoing example the critical data optionally may, at each step of the transfer path, be parsed into portions that are individually encrypted, transferred, and destroyed sequentially one after another. 
         [0020]    Various other methods of backup and alternative embodiments can be adapted to a particular environment and type of data management or transfer.