Fault Attacks on RSA Public Keys: Left-To-Right Implementations Are Also Vulnerable

After attacking the RSA by injecting fault and corresponding countermeasures, works appear now about the need for protecting RSA public elements against fault attacks. We provide here an extension of a recent attack [BCG08] based on the public modulus corruption. The difficulty to decompose the ”Left-To-Right” exponentiation into partial multiplications is overcome by modifying the public modulus to a number with known factorization. This fault model is justified here by a complete study of faulty prime numbers with a fixed size. The good success rate of this attack combined with its practicability raises the question of using faults for changing algebraic properties of finite field based cryptosystems.