The spectral decomposition of cryptography into its life-giving components yields an interlaced network of
tangential and orthogonal disciplines that are nonetheless invariably grounded by the same denominator: their
implementation on commodity computing platforms where efficiency is the overarching dogma. The term efficiency,
however, only vaguely captures the intricacies of the field of cryptographic optimisation and can be gauged only in
relation to the underlying architectures and their corresponding metrics. In software, these criteria come in the
form of memory or instruction cycles of minimisation. Whereas in hardware environments, designers commonly target
circuit area or latency reductions.

In this thesis, we blissfully ignore the software realm and fully concentrate our efforts on cryptographic hardware
implementations, i.e., application-specific integrated circuits, in an undertaking that encompasses endeavours
ranging from classic optimisation work of existing algorithms to the conception of novel constructions. This
thesis unfolds over two books:

The first book is a treatise on the energy consumption of cryptographic circuits, an under-represented metric in
the canon of optimisation literature. We commence by devising an energy model for authenticated encryption schemes
by investigating the consumptive behaviour of lightweight schemes that are bootstrapped via block ciphers. We then
turn our gazes over to hardware-based stream ciphers and propose the first heuristic energy model for this class of
algorithms that enables us to design the currently most energy-efficient stream cipher suited for the encryption of
larger bulks of data. We conclude this section with the proposal of an energy-efficient small-state stream cipher.

The second book gathers contributions in various other disciplines such as serialisation of block cipher
circuits through which we obtain the smallest known implementation of the Advanced Encryption Standard. We then
divert our attention toward encryption algorithms for high-throughput networks, as found in the upcoming 6G
telecommunication channels. And we design an authenticated encryption scheme that is both secure in the
post-quantum setting and reaches unparalleled throughput rates in the Terabit range. Ultimately, the thesis is
concluded with an optimisation work on a side-channel-protected threshold implementation of a lightweight family of
block ciphers.