Common modulus attacks on small private exponent RSA and some fast variants (in practice)

In this work we re-examine two common modulus attacks on RSA. First, we show that Guo's continued fraction attack works much better in practice than previously expected. Given three instances of RSA with a commonmodulus N and private exponents each smaller than N0.33, the attack can factor the modulus about 93% of the time in practice. The success rate of the attack can be increased up to almost 100% by including a relatively small exhaustive search. Next, we consider Howgrave-Graham and Seifert's lattice-based attack and show that a second necessary condition for the attack exists that limits the bounds (beyond the original bounds) once n ≥ 7 instances of RSA are used. In particular, by construction, the attack is limited to private exponents at most N0.5–ε, given sufficiently many instances, instead of the original bound of N1–ε