In 2013, the US National Security Agency proposed two new families of lightweight block ciphers: SIMON and SPECK. Currently, linear and differential cryptanalytic results for SIMON are available in the literature but no fault attacks have been reported so far on these two cipher families. In this paper, we show that these families of ciphers are vulnerable to differential fault attacks. Specifically, we demonstrate two fault attacks on SIMON and one fault attack on SPECK. The first attack on SIMON assumes a bit-flip fault model and recovers the n-bit last round key of SIMON using n/2 bit faults. The second attack on SIMON uses a more practical, random byte fault model and requires n/8 faults on average to retrieve the last round key. The attack presented on SPECK also assumes a bit-flip fault model and recovers the n-bit last round key of SPECK using n/3 bit faults on average.

Researchers have demonstrated the ineffectiveness of deterministic countermeasures and emphasized on the use of randomness for protecting cryptosystems against fault attacks. One such countermeasure for AES was proposed in LatinCrypt 2012, which masks the faulty output with secret values. However this countermeasure does not affect the erroneous byte in the faulty computation of the last AES round and is thus shown to be flawed in FDTC 2013. In this paper, we examine the Latin-Crypt 2012 countermeasure in detail and identify its additional flaws in order to develop a robust countermeasure. We bring out the major weakness in the infection mechanism of the LatinCrypt 2012 countermeasure which not only makes the attack of FDTC 2013 much more flexible, but also enables us to break this seemingly complex countermeasure using Piret & Quisquater's attack that requires only 8 pairs of correct and faulty ciphertexts. Finally, we combine all our observations and propose a countermeasure that employs randomness much more effectively to prevent state-of-the-art differential fault attacks against AES.

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Pattern lock scheme in which users connect 4-9 dots in a 3 × 3 grid is one of the most popular authentication methods on mobile devices. However, numerous research studies show that users choose patterns from a small space which makes them vulnerable to a variety of attacks such as guessing attacks, shoulder-surfing attacks and smudge attacks.In this work, we enhance the existing 3 × 3 interface with a visual indicator mechanism and demonstrate how this slight modification can influence users' pattern choices, thereby improving the security of the pattern lock scheme. We refer to this enhanced interface as TinPal. As users draw their pattern, TinPal highlights the next set of unconnected dots that can be reached from the currently connected dot. We gauge the impact of this highlighting mechanism on users' pattern choices by performing a comparative study of two groups, where one group creates pattern using the existing interface while the other group creates pattern using TinPal. The study results show that participants who used TinPal created more secure patterns than participants who used the existing interface.