An Introduction to the Theory of Elliptic Curves [pdf]
math.brown.edu
math.brown.edu
DJ Bernstein maintains the SafeCurves website and explains the foregoing in greater detail; the site also tracks security assessments on specific curves. Some are actively used and others are either not well-studied or are just toy examples.
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Theoretical computer science (e.g. complexity theory). :-) Always add this application to a research proposal.