This will be the fourth of six cryptography primer sessions exploring the basics of modern cryptography. In this session, we’ll explore primality testing, elliptic curve cryptosystems, and lattice-based cryptosystems. Subsequent sessions (on alternating Fridays) are expected to include the following topics. Depending on the interests of the participants, other topics may be included or substituted. Attacks, vulnerabilities, and practical considerations Applications including zero-knowledge, secret sharing, homomorphic encryption, and election protocols.