A new study has demonstrated that it's possible for passive network attackers to obtain private RSA host keys from a vulnerable SSH server by observing when naturally occurring
computational faults that occur while the connection is being established.
The Secure Shell (SSH) protocol is a method for securely transmitting commands and logging in to a computer over an unsecured network. Based on a client-server architecture, SSH uses cryptography to authenticate and encrypt connections between devices.
A
host key is a cryptographic key used for authenticating computers in the SSH protocol. Host keys are key pairs that are typically generated using public-key cryptosystems like
RSA.
"If a signing implementation using CRT-RSA has a fault during signature computation, an attacker who observes this signature may be able to compute the signer's private key," a group of academics from the University of California, San Diego, and Massachusetts Institute of Technology
said in a paper this month.
