Universal forgery on Sekhar's signature scheme with message recovery.
F. Laguillaumie, J. Traore, and D. Vergnaud.

Owing to the abundance of electronic applications of digital signatures, many additional properties are needed. Recently, Sekhar [Sekhar, M. R. (2004). Signature scheme with message recovery and its application. Int. J. Comput. Math., 81(3), 285-289.] proposed three signature schemes with message recovery designed to protect the identity of the signer. In this setting, only a specific verifier can check the validity of a signature, and he can transmit this conviction to a third party. In this note, we show that this protocol is totally insecure, as it is universally forgeable under a no-message attack. In other words, we show that anyone can forge a valid signature of a user on an arbitrary message. The forged signatures are unconditionally indistinguishable (in an information theoretical sense) from properly formed signatures.