Physical Unclonable Functions (PUFs) are innovative circuit primitives that extract secrets from physical characteristics of integrated circuits (ICs). We present PUF designs that exploit inherent delay characteristics of wires and transistors that differ from chip to chip, and describe how PUFs can enable low-cost authentication of individual ICs and generate volatile secret keys for cryptographic operations.

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Physical unclonable functions for device authentication and secret key generation

Physical Unclonable Functions for Device Authentication and Secret Key Generation

In this paper, we define and explore proofs of retrievability (PORs). A POR scheme enables an archive or back-up service (prover) to produce a concise proof that a user (verifier) can retrieve a target file F, that is, that the archive retains and reliably transmits file data sufficient for the user to recover F in its entirety.A POR may be viewed as a kind of cryptographic proof of knowledge (POK), but one specially designed to handle a large file (or bitstring) F. We explore POR protocols here in which the communication costs, number of memory accesses for the prover, and storage requirements of the user (verifier) are small parameters essentially independent of the length of F. In addition to proposing new, practical POR constructions, we explore implementation considerations and optimizations that bear on previously explored, related schemes.In a POR, unlike a POK, neither the prover nor the verifier need actually have knowledge of F. PORs give rise to a new and unusual security definition whose formulation is another contribution of our work.We view PORs as an important tool for semi-trusted online archives. Existing cryptographic techniques help users ensure the privacy and integrity of files they retrieve. It is also natural, however, for users to want to verify that archives do not delete or modify files prior to retrieval. The goal of a POR is to accomplish these checks without users having to download the files themselves. A POR can also provide quality-of-service guarantees, i.e., show that a file is retrievable within a certain time bound.

PORs: Proofs of Retrievability for Large Files

Pors: proofs of retrievability for large files

In recent years, IP protection of FPGA hardware designs has become a requirement for many IP vendors. In [34], Simpson and Schaumont proposed a fundamentally different approach to IP protection on FPGAs based on the use of Physical Unclonable Functions (PUFs). Their work only assumes the existence of a PUF on the FPGAs without actually proposing a PUF construction. In this paper, we propose new protocols for the IP protection problem on FPGAs and provide the first construction of a PUF intrinsic to current FPGAs based on SRAM memory randomness present on current FPGAs. We analyze SRAM-based PUF statistical properties and investigate the trade offs that can be made when implementing a fuzzy extractor.

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FPGA Intrinsic PUFs and Their Use for IP Protection

Modern cryptographic protocols are based on the premise that only authorized participants can obtain secret keys and access to information systems. However, various kinds of tampering methods have been devised to extract secret keys from conditional access systems such as smartcards and ATMs. Arbiter-based physical unclonable functions (PUFs) exploit the statistical delay variation of wires and transistors across integrated circuits (ICs) in manufacturing processes to build unclonable secret keys. We fabricated arbiter-based PUFs in custom silicon and investigated the identification capability, reliability, and security of this scheme. Experimental results and theoretical studies show that a sufficient amount of inter-chip variation exists to enable each IC to be identified securely and reliably over a practical range of environmental variations such as temperature and power supply voltage. We show that arbiter-based PUFs are realizable and well suited to build, for example, key-cards that need to be resistant to physical attacks.

Extracting secret keys from integrated circuits

Physical Unclonable Functions (PUFs) for authentication can be implemented in a variety of electronic devices including FPGAs, RFIDs, and ASICs. In some implementations, challenge-response pairs corresponding to individual PUFs can be enrolled and used to determine authentication data, which may be managed in a database. Later when a target object with a PUF is intended to be authenticated a set (or subset) of challenges are applied to each PUF device to authenticate it and thus distinguish it from others. In some examples, authentication is achieved without requiring complex cryptography circuitry implemented on the device. Furthermore, an authentication station does not necessarily have to be in communication with an authority holding the authentication data when a particular device is to be authenticated.

Authentication with physical unclonable functions

We present an adaptive tree-log scheme to improve the performance of checking the integrity of arbitrarily large untrusted data, when using only a small fixed-sized trusted state. Currently, hash trees are used to check the data. In many systems that use hash trees, programs perform many data operations before performing a critical operation that exports a result outside of the program's execution environment. The adaptive tree-log scheme we present uses this observation to harness the power of the constant runtime bandwidth overhead of a log-based scheme. For all programs, the adaptive tree-log scheme's bandwidth overhead is guaranteed to never be worse than a parameterizable worst case bound. Furthermore, for all programs, as the average number of times the program accesses data between critical operations increases, the adaptive tree-log scheme's bandwidth overhead moves from a logarithmic to a constant bandwidth overhead.

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Towards constant bandwidth overhead integrity checking of untrusted data

Subsets of multiple signal generator circuits embodied in a device are selected, and then a volatile value for the device is generated from the selected subsets. The volatile value may be used for authentication of the device and/or for cryptographic procedures performed on the device. The signal generator circuits may each comprise an oscillator circuit, and the selection of the subsets may be according to a comparison of the outputs of the subsets of circuits, for example, according to a comparison of output oscillation frequencies.

Gookwon Edward Suh

Papers

Extracting secret keys from integrated circuits

Authentication with physical unclonable functions

Towards constant bandwidth overhead integrity checking of untrusted data

Signal generator based device security

Method,integrated circuit,and computer program product for signal generator based device security