Comment on 'Targeted Ciphers for Format-Preserving Encryption' from Selected Areas in Cryptography 2018

Format-preserving encryption (FPE) allows encrypting plaintexts while preserving a specific format. In Selected Areas in Cryptography 2018, two targeted ciphers were proposed as new FPE schemes. The second scheme was designed with an algorithm called Mix-Swap-Unmix that is shown to be equivalent to a particular matching exchange process under a specific setting. In this comment paper, we prove that the matching exchange process is invalid. As a result, this equivalence does not exist.

Automated summary

Format-preserving encryption (FPE) is a method that allows encrypting data while maintaining its original format. In a cryptography study from 2018, two new FPE schemes were proposed, with the second one using the Mix-Swap-Unmix algorithm to achieve a specific matching exchange process. However, it was later proven that this matching exchange process is invalid, leading to the conclusion that the equivalence does not exist.