the real power of a PUF is its ability to be different between devices but simultaneously to be the same under different environmental conditions on the same device. Error correction In many applications, it is important that the output is stable. If the PUF is used for a key in cryptographic algorithms, it is necessary that error correction be done to correct any errors caused by the underlying physical processes and reconstruct exactly the same key each time under all operating conditions. In principle there are two basic concepts: Pre-Processing and Post-Processing Error Correction Code (ECC). On-chip ECC units increase size, power, and data processing time overheads; they also expose vulnerabilities to power analysis attacks that attempt to model the PUF mathematically. Alternatively, some PUF designs like the EC-PUF do not require an on-chip ECC unit. Strategies have been developed which lead SRAM PUF to become more reliable over time without degrading the other PUF quality measures such as security and efficiency. Research at Carnegie Mellon University into various PUF implementations found that some error reduction techniques reduced errors in PUF response in a range of ~70 percent to ~100 percent. Research at the University of Massachusetts Amherst to improve the reliability of SRAM PUF-generated keys posited an error correction technique to reduce the error rate. Joint reliability–secrecy coding methods based on transform coding are used to obtain significantly higher reliabilities for each bit generated from a PUF such that low-complexity error-correcting codes such as BCH codes suffice to satisfy a block error probability constraint of 1 bit errors out of 1 billion bits. Nested polar codes are used for vector quantization and error correction jointly. Their performance is asymptotically optimal in terms of, for a given blocklength, the maximum number of secret bits generated, the minimum amount of private information leaked about the PUF outputs, and minimum storage required. The fuzzy commitment scheme and fuzzy extractors are shown to be suboptimal in terms of the minimum storage. Availability PUF technology can be licensed from several companies including eMemory, or its subsidiary, PUFsecurity, Enthentica, ICTK, Intrinsic ID, Invia, QuantumTrace, Granite Mountain Technologies and Verayo. PUF technology has been implemented in several hardware platforms including Microsemi SmartFusion2, NXP SmartMX2, Coherent Logix HyperX, InsideSecure MicroXsafe, Altera Stratix 10, Redpine Signals WyzBee and Xilinx Zynq Ultrascale+. Vulnerabilities In 2011, university research showed that delay-based PUF implementations are vulnerable to side-channel attacks and recommends