Literature Review - (Quantum-Safe) Cryptographic Combiners and Hybrid Security

In this document, we report on a literature review, conducted by the authors of the document, on the topic of combiners and hybrid security. Due to their relevance in the context of PKIs, the main focus is on combiners for public-key encryption schemes (or KEMs) and digital signature schemes; combiners for other cryptographic tasks (like hash combiners etc.) are not covered. The purpose of this report is two-fold: (1) we want to give a high-level overview on the questions and problems that are being considered and studied in the scientific literature on the topic of combinersand hybrid security, and (2) we want to give a brief summary of the results and achievements in the articles covered in this report. The latter in particular should facilitate the decision making, when one
is searching for a particular study/result.