This book constitutes the refereed proceedings of the Cryptographer's Track at the RSA Conference 2021, CT-RSA 2021, held in San Francisco, CA, USA, in May 2021.* The 27 full papers presented in this volume were carefully reviewed and selected from 100 submissions. CT-RSA is the track devoted to scientific papers on cryptography, public-key to symmetric-key cryptography and from crypto-graphic protocols to primitives and their implementation security. *The conference was held virtually.