Cryptanalysis of Hash-Based Tamed Transformation and Minus Signature Scheme

In 2011, wang et al. proposed a security enhancement method of Multivariate Public Key Cryptosystems (MPKCs), named Extended Multivariate public key Cryptosystems (EMC). They introduced more variables in an original MPKC by a so-called Hash-based Tamed (HT) transformation in order to resist existing attack on the original MPKC. They proposed Hash-based Tamed Transformation and Minus (HTTM) signature scheme which combined EMC method with minus method. Through our analysis, the HTTM is not secure as they declared. If we can forge a valid signature of the original MPKC-minus signature scheme, we could forge a valid signature of HTTM scheme successfully.