How (Not) to design strong-RSA signatures

This paper considers strong-RSA signature schemes built from the scheme of Cramer and Shoup. We present a basic scheme encompassing the main features of the Cramer-Shoup scheme. We analyze its security in both the random oracle model and the standard model. This helps us to spot potential security flaws. As a result, we show that a seemingly secure signature scheme (Int. J. of Security and Networks, 2006) is universally forgeable under a known-message attack. In a second step, we discuss how to turn the basic scheme into a fully secure signature scheme. Doing so, we rediscover several known schemes (or slight variants thereof).