Abstract: Recently, Hwang et al proposed a (t,n) threshold-proxy (c,m) threshold-signature schemes, in which only any t or more original signers of n original signers can authorize a proxy group of m proxy signers and then only c or more proxy signers can cooperatively generate threshold-proxy threshold-signature. In this scheme, they claimed that original signers cannot forge the proxy signature and the proxy signers cannot forge signature on behalf of the original signers. However, in this paper, we will give a attack to show that their scheme can not resist impersonation attacks.

Key words: cryptanalysis, impersonate attacks, threshold-proxy threshold-signature