Recover a RSA Private Key from a TLS Session with Perfect Forward Secrecy

by Marco Ortisi Sept. 16, 2017 via submitted by belen_caty

In certain circumstances it is possible to derive the private key of server regardless of the size of the used modulus. Even RSA keys of 4096 bits can be factored at the cost of a few CPU cycles and computational resources. All that needed is the generation of a faulty digital signature from server, an event that can be observed when occurring certain conditions such as CPU overheating, RAM errors or other hardware faults. Because of these premises, devices like firewall, switch, router and other embedded appliances are more exposed than traditional IT servers or clients. During the talk, the author will explain the theory behind the attack, how common the factors are that make it possible and his custom practical implementation of the technique. At the end, a proof-of-concept, able to work both in passive mode (i.e. only by sniffing the network traffic) and in active mode (namely, by participating directly in the establishment of TLS handshakes), will be released.