On the security of two identity-based signature schemes based on pairings

ID-based signature enables users to verify signatures using only public identifier. Very recently, Rossi and Schmid (2015) 9 proposed two identity-based signature schemes along with the application to group communications. Unfortunately, by proposing concrete attack, we demonstrate that the former scheme is insecure against forgery attack, while the latter scheme has been totally broken in the sense that the signing key can be recovered from the valid signature easily. ID-based signature enables users to verify signatures using only public identifier.Rossi and Schmid proposed two provably-secure ID-based signature schemes recently.We show that both schemes are insecure against the forgery and key disclosure attack.