- Internet of Things (IoT) is an integral part of application domains such as smart-home, digital healthcare, smart grid systems and vehicular networks. Various standard public key cryptography techniques (e.g., key exchange, public key encryption, digital signature) are available to provide fundamental security services for IoTs. However, despite their pervasiveness and well-proven security, they also have been shown to be highly costly for embedded devices in terms of energy and time consumption. These standard techniques introduce high delays that may hinder the safe operation of the IoT applications (e.g., smart grids, vehicular networks). Hence, it is a critical task to improve the efficiency of standard cryptographic services, while preserving their desirable security properties simultaneously.
To address the efficiency of the public key cryptography in IoT setting, we propose (i) a series of algorithmic improvements over key exchange and public key encryption schemes and (ii) an attack and an efficient fix to a real-time digital signature scheme that benefits aggregate signatures.
In this thesis, we first exploit synergies among various cryptographic primitives (key exchange and public key encryption schemes) with algorithmic optimizations to substantially reduce the energy consumption of standard cryptographic techniques on embedded devices. Our contributions are: (i) We harness special pre-computation techniques, which have not been considered for some important cryptographic standards to boost the performance of key exchange, integrated encryption, and hybrid constructions. (ii) We provide self-certification for these techniques to push their performance to the edge. (iii) We implemented our techniques and their counterparts on 8-bit AVR ATmega 2560 and evaluated their performance. We used microECC library and made the implementations on NIST-recommended secp192 curve, due to its standardization. Our experiments confirmed significant improvements on the battery life (up to 7x) while preserving the desirable properties of standard techniques. Moreover, to the best of our knowledge, we provide the first open-source framework including such set of optimizations on low-end devices.
Delay-aware signatures also play an important role to provide authentication for critical IoT applications. A recent attempt to derive signer-efficient digital signatures from aggregate signatures was made in a signature scheme referred to as Structure-free Compact Rapid Authentication (SCRA) (IEEE TIFS 2017). In this thesis, we show that SCRA generic design leaks information about the private keys. For pqNTRUsign instantiation, this leakage can be exploited to recover all private key components with an overwhelming probability by observing only 8192 signatures. We then propose a new signature scheme that we call as Fast Authentication with Aggregate Signatures (FAAS), which can transform any single-signer (k-element extraction secure) aggregate signature scheme into a signer-efficient signature scheme. We develop two efficient instantiations of FAAS, namely, FAAS-RSA and FAAS-NTRU, both of which achieve a low end-to-end cryptographic delay while
FAAS-NTRU also offers a post-quantum promise. Our experiments confirmed that FAAS instantiations offer very fast signature generation with up to 100x speed improvements over their base schemes. Moreover, FAAS signature generation avoids operations such as exponentiation and Gaussian sampling, and therefore offers an improved side-channel resiliency against attacks targeting these operations. All these desirable properties come with the cost of a larger private key and a slight increase in the signature size.