###### Abstract  
Cryptoysystems are widely used in a growing number of embedded applications, such as smart cards, smart phones, Internet of Things (IoT) devices, and so on. Although these cryptosystems have been proven to be safe using mathematical tools, they are potentially susceptible to physical attacks which exploit additional sources of information, including timing information, power consumption, electromagnetic emissions (EM), and sound, amongst others. Introduced by [PERSON], these types of attacks are referred to as side-channel attacks (SCAs) [1, 2]. These attacks pose a very serious threat to embedded systems with cryptographic algorithms. There has been a great deal of effort put into finding various SCAs and developing secure counter-measures, recently [3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16]. This special issue has been organized to provide a possibility for researchers in the area of SCAs to highlight the most recent and exciting technologies. The research papers selected for this special issue represent recent progress in the field, including power analysis attacks [17, 18, 19], cache-based timing attacks [20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41], system-level counter-measures [42, 43, 44, 45, 46, 47, 48], and so on [49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60]. The thirteen papers in this special issue can be classified into the following four research themes:  
**Power analysis attacks and counter-measures:** This special issue contains various power analysis attacks and counter-measures on well-known crypto algorithms: Elliptic curve cryptosystems (ECCs), the block cipher SEED, and the post-quantum cryptographies (PQCs). A new side channel leakage of the SEED in financial IC cards in the Republic of Korea was detected in [61]; and new vulnerabilities, using a single power consumption trace obtained in the elliptic curve scalar multiplication algorithm, were established in [62, 63]. Recently, PQCs, cryptographic algorithms executed on a classical computer which are expected to be secure against adversaries with quantum computers, have been actively studied. This special issue contains two papers about power analysis attacks on PQCs: The well-known NTRU algorithm, and a cumulative distribution table (CDT) sampler used in the lattice-based PQCs [64, 65]. **Cache-based timing attacks:** This special issue contains two research papers with regard to cache-based timing attacks, utilizing the timing difference between cache hits and cache misses. One paper proposes a new constant-time method for RSA modular exponentiation, which is resistant against fine-grained cache attacks [66]. The other one shows a non-access attack, a novel approach for exploiting the information gained from cache misses [67]. **System-level counter-measures and their weaknesses:** Two research papers in this special issue introduce a new system-level counter-measure and a new vulnerability of the existing physically un-clonable function (PUF), respectively. One paper deals with the re-keying scheme, a system-level counter-measure against SCAs, which makes attackers unable to collect enough power consumption traces for their analyses [68]. The authors of this paper define a new security model and propose two provably secure re-keying schemes. The other paper shows that a PUF key can be derived from a chaotic circuit [69]. **Recent technologies in the field of Side Channel Attacks:** This special issue also contains papers documenting recent technologies in the field of SCAs: A machine-learning based side-channel evaluation technique [70], a Merkle tree-based on-line data authentication technique with leakage resilience [71], an ID-based side-channel authentication technique [72], and a technique to distinguish ad-related network behavior [73]. In summary, this special issue contains many excellent studies, covering a wide range of SCA-related topics. This collection of 13 papers is highly recommended, and is believed to benefit readers in various aspects.