Making secure TCP connections resistant to server failures

Methods are presented to increase resiliency to server failures by migrating long running, secure TCP-based connections to backup servers, thus mitigating damage from servers disabled by attacks or accidental failures. The failover mechanism described is completely transparent to the client. Using these techniques, simple, practical systems can be built that can be retrofitted into the existing infrastructure, i.e. without requiring changes either to the TCP/IP protocol, or to the client system. The end result is a drop-in method of adding significant robustness to secure network connections such as those using the secure shell protocol (SSH). As there is a large installed universe of TCP-based user agent software, it will be some time before widespread adoption takes place of other approaches designed to withstand these kind of service failures; our methods provide an immediate way to enhance reliability, and thus resistance to attack, without having to wait for clients to upgrade software at their end. The practical viability of our approach is demonstrated by providing details of a system we have built that satisfies these requirements.