About the Fujisaki-Okamoto Transformation in the Code-Based Algorithms of the NIST Post-quantum Call

Post-quantum encryption schemes use variants of the Fujisaki-Okamoto transformation in order to construct a highly secure key encapsulation mechanism from a weakly secure public key encryption scheme. In the third round of the NIST post-quantum cryptography standardization call, all the candidates for the key encapsulation mechanism category use some of these transformations. This work studies how the mentioned transformations are applied in the code-based candidates of the NIST third round. These are Classic McEliece (finalist), BIKE (alternative) and HQC (alternative). Studying the differences between the transformations gives a better understanding of these candidates.