  Multiple-vantage-point domain control validation (multiVA) is an emerging
defense for mitigating BGP hijacking attacks against certificate authorities.
While the adoption of multiVA is on the rise, little work has quantified its
effectiveness against BGP hijacks in the wild. We bridge the gap by presenting
the first analysis framework that measures the security of a multiVA deployment
under real-world network configurations (e.g., DNS and RPKI). Our framework
accurately models the attack surface of multiVA by 1) considering the attacks
on DNS nameservers involved in domain validation, 2) considering deployed
practical security techniques such as RPKI, 3) performing fine-grained
internet-scale analysis to compute multiVA resilience (i.e., how difficult it
is to launch a BGP hijack against a domain and get a bogus certificate under
multiVA). We use our framework to perform a rigorous security analysis of the
multiVA deployment of Let's Encrypt, using a dataset that consists of about 1
million certificates and 31 billion DNS queries collected over four months. Our
analysis shows while DNS does enlarge the attack surface of multiVA, the of
Let's Encrypt's multiVA deployment still offers an 88% median resilience
against BGP hijacks, a notable improvement over 76% offered by
single-vantage-point validation. RPKI, even in its current state of partial
deployment, effectively mitigates BGP attacks and improves the security of the
deployment by 15% as compared to the case without considering RPKI. Exploring
11,000 different multiVA configurations, we find that Let's Encrypt's
deployment can be further enhanced to achieve a resilience of over 99% by using
a full quorum policy with only two additional vantage points in different
public clouds.
