Physical Security of Cryptographic Algorithm Implementations

This thesis deals with physical attacks on implementations of cryptographic algorithms and countermeasures against these attacks. Physical attacks exploit properties of an implementation to recover secret cryptographic keys. Particularly vulnerable to physical attacks are embedded devices. In the area of side-channel analysis, this thesis addresses attacks that exploit observations of power consumption or electromagnetic leakage of the device and target symmetric cryptographic algorithms. First, this work proposes a new combination of two well-known attacks that is more efficient than each of the attacks individually. Second, this work studies attacks exploiting leakage induced by microprocessor cache mechanism, suggesting an algorithm that can recover the secret key in the presence of uncertainties in cache event detection from side-channel acquisitions. Third, practical side-channel attacks are discovered against the AES engine of the AVR XMEGA, a recent versatile microcontroller. In the area of fault analysis, this thesis extends existing attacks against the RSA digital signature algorithm implemented with the Chinese remainder theorem to a setting where parts of the signed message are unknown to the attacker. The new attacks are applicable in particular to several widely used standards in modern smart card applications. In the area of countermeasures, this work proposes a new algorithm for random delay generation in embedded software. The new algorithm is more efficient than the previously suggested algorithms since it introduces more uncertainty for the attacker with less performance overhead. The results presented in this thesis are practically validated in experiments with general-purpose 8-bit AVR and 32-bit ARM microcontrollers that are used in many embedded devices