Physical Characterization of Arbiter PUFs

As intended by its name, Physically Unclonable Functions (PUFs) are considered as an ultimate solution to deal with insecure stor- age, hardware counterfeiting, and many other security problems. How- ever, many different successful attacks have already revealed vulnera- bilities of certain digital intrinsic PUFs. Although settling-state-based PUFs, such as SRAM PUFs, can be physically cloned by semi-invasive and fully-invasive attacks, successful attacks on timing-based PUFs were so far limited to modeling attacks. Such modeling requires a large sub- set of challenge-response-pairs (CRP) to successfully model the targeted PUF. In order to provide a final security answer, this paper proves that all arbiter-based (i.e. controlled and XOR-enhanced) PUFs can be com- pletely and linearly characterized by means of photonic emission analy- sis. Our experimental setup is capable of measuring every PUF-internal delay with a resolution of 6 picoseconds. Due to this resolution we in- deed require only the theoretical minimum number of linear independent equations (i.e. physical measurements) to directly solve the underlying inhomogeneous linear system. Moreover, we neither require to know the actual PUF challenges nor the corresponding PUF responses for our physical delay extraction. On top of that devastating result, we are also able to further simplify our setup for easier physical measurement han- dling. We present our practical results for a real arbiter PUF implemen- tation on a Complex Programmable Logic Device (CPLD) from Altera manufactured in a 180 nanometer process

On Borrowed Time -- Preventing Static Power Side-Channel Analysis

In recent years, static power side-channel analysis attacks have emerged as a serious threat to cryptographic implementations, overcoming state-of-the-art countermeasures against side-channel attacks. The continued down-scaling of semiconductor process technology, which results in an increase of the relative weight of static power in the total power budget of circuits, will only improve the viability of static power side-channel analysis attacks. Yet, despite the threat posed, limited work has been invested into mitigating this class of attack. In this work we address this gap. We observe that static power side-channel analysis relies on stopping the target circuit's clock over a prolonged period, during which the circuit holds secret information in its registers. We propose Borrowed Time, a countermeasure that hinders an attacker's ability to leverage such clock control. Borrowed Time detects a stopped clock and triggers a reset that wipes any registers containing sensitive intermediates, whose leakages would otherwise be exploitable. We demonstrate the effectiveness of our countermeasure by performing practical Correlation Power Analysis attacks under optimal conditions against an AES implementation on an FPGA target with and without our countermeasure in place. In the unprotected case, we can recover the entire secret key using traces from 1,500 encryptions. Under the same conditions, the protected implementation successfully prevents key recovery even with traces from 1,000,000 encryptions

QKD and high-speed classical data hybrid metropolitan network

Quantum Key Distribution (QKD) is currently receiving much attention as it provides a secure source of encryption keys. Discrete-Variable QKD (DV-QKD) is possible for single photon transmission in QKD to-coexist with and encode classical wavelength division multiplexed (WDM) data with appropriate system design. Nevertheless, previous QKD field trials adopted either or both of key relay via trusted nodes and transparent link via optical switching. The former requires guaranteed physical security of the relay nodes, but can expand key distribution distance arbitrarily. The latter can realize key establishment for more users with less complexity of key management over an untrusted network. To realise the adaption of the QKD system for future high speed and long distance metropolitan world exploitation at lower cost, there has to be investigations on existing fibre infrastructures. Prior to this work, previous researches over similar distances feature extremely low secure key rates. For example, the Swiss Quantum Network between three sites displayed secure bit rates of 2.5 kbps at a fibre length of 17km. Quantum Key distribution within the 25km Cambridge Quantum Network have demonstrated the highest long-term secure key rates yet demonstrated in a field trial of at least 2.5Mb/s which is the fastest and much higher than 0.8 kbps which was reached over the similar channel loss field trial up to date. Additional field trials have been performed on the UK Quantum Network using a 66km path having 16dB loss. Combined wavelength division multiplexed 2 x 100 Gb/s traffic encrypted using QKD co-existing on the same fibres has operated for several months, with a long-term key rate of 80kb/s that is also faster than any other similar long-term QKD trial systems. In addition to this advanced commercial QKD system, there have been secure key rate analysis comparisons between laboratory fibre coils and practical field trials more than field trials only conducted before.These comparisons help to identify factors that limit future QKD network scale in both quantity and quality aspects. Also, the limit for the highest secure key rate at longest fibre length QKD in the multiplexing environment is discussed and determined in this research thesis. Nevertheless, in this thesis, improvements have been made to minimise the corresponding negative effects by investigations on the dependence of temperature have been done in order to ensure system operation environment effects. It was found from the trial results that there exists a relationship between temperature and secure key rate and further study has been done to evaluate the system sensitivity to operating temperature. Although the conventional DV-QKD system, original BB84 coding scheme, was designed to exploit the quantum properties of single photon polarization states, the trial equipment operates based upon the phase coding schemes. These coding schemes are based on the properties of interferometers and the coding is implemented by changing the relative optical path lengths or phase between the internal arms of the interferometer, while in the real transmission environment, temperature or polarization variation happens unpredictably. The existing polarisation controllers operate at relative low speed align within the interferometer, which slows to operation environment such as a punch to fibre causing phase difference. Therefore, in this project, there has been an improvement in the QKD-WDM system performance by adding an external polarization controller to minimize the Raman noise and increase the secure key rate at the longest fibre length up to date. In Summary, transmitting quantum keys over a coil of fibre in the lab differs a lot from actually putting it in the ground. This work contrasts the world fastest QKD system at the longest distance in field trials with lab fibre reels and then characterises and identifies two of the key factors, temperature and polarizations, influencing performance in practical wavelength-multiplexed secure communication systems. This is a significant step towards the coexistence of the quantum and conventional data channels on the same fibre for metropolitan networks and paves a way for an information-secure communication infrastructure