DoubleCheck: Multi-path verification against man-in-the-middle attacks

Abstract

Abstract-Self-signed certificates for SSL and self-generated hosts keys for SSH are popular zero-cost, simple alternatives to public key infrastructure (PKI). They provide security against man-in-the-middle attacks, as long as the the client connecting to those services knows the certificates or host keys a priori. A simple solution used in practice is to trust the certificate or the host key when the client connects to a server for the first time. This approach is susceptible to man-in-the-middle attacks, a fact exploited by adversaries in a variety of attacks against unsuspecting users. We develop a simple and scalable solution named DoubleCheck to protect against such attacks. Our solution is achieved by retrieving the certificate from a remote host using multiple alternate paths. Our scheme does not require any new infrastructure; we make use of the Tor anonymity system to reach the destination using multiple independent paths. Hence our solution is easy to deploy in practice. Our solution does not introduce any privacy concerns. We have implemented DoubleCheck as SSH and Firefox extensions, demonstrating its practicality. Our experimental evaluation shows that the impact of DoubleCheck on performance is minimal, since the Tor network is used only for retrieving the certificate for the first time, while the data transfer and subsequent connection establishment follow normal routing rules. Our scheme is an effective way of mitigating the impact of man-in-the-middle attacks without requiring new infrastructure and at low overhead.

Enhanced Certificate Transparency and End-to-End Encrypted Mail

“…Certificate pinning addresses the problem of untrustworthy CAs, by restricting in the client browser parameters concerning the set of CAs that are considered entitled to certify the key for a given domain [14], [15]. Crowd-sourcing techniques have been proposed in order to detect untrustworthy CAs, by enabling a browser to obtain warnings if the certificates it is offered are out of line with those that other people are being offered [16], [17], [18], [19]. In another direction, certificate transparency [20] is an approach which aims to prevent certificate authorities from issuing public key certificates for a domain without being visible to the owner of the domain.…”

“…Proposals in this vein include the SSL Observatory [31]; Certificate Patrol [32]; Perspectives [33]; DoubleCheck [34]; CertLock [35]; Covergence [36]; and TACK (2012) [37]. There are also approaches based on using DNS, such as DANE [38]; and CAge (2013) [39].…”

Laribus: privacy-preserving detection of fake SSL certificates with a social P2P notary network

“…These privacy concerns are embraced by DoubleCheck [39], which suggests that whenever a client connects to a SSL web server it should retrieve its certificate additionally via the Tor network for comparison. An extension of this design is DetecTor [40], which suggests to retrieve each certificate over multiple Tor circuits using different exit nodes for increased trust.…”

CAge: Taming Certificate Authorities by Inferring Restricted Scopes

“…Multi-path probing [2,10,13] has been suggested as a way to reduce reliance on CAs; however, it necessitates the availability and access to trusted notaries. Browser extensions have also been proposed to pin previously seen certificates or CAs to domains [6,9,12].…”