66 lines
3.4 KiB
Markdown
66 lines
3.4 KiB
Markdown
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title = "DNSSEC + DANE: Part 1"
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date = "2013-09-14"
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tags = ["security", "technical", "DANE"]
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#### Problem
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Communications on the Internet overwhelmingly rely on SSL/TLS for protection.
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There are two forms of protection this is meant to provide - from snooping of
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traffic, and from impersonation. The first of those gets a lot of attention
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but, unless we have the latter as well, an attacker can snoop on your traffic
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by [performing a man-in-the-middle attack on you with a dodgy
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certificate](http://falkvinge.net/2013/09/12/the-nsa-and-u-s-congress-has-destroyed-ssl-we-must-rebuild-web-security-from-the-ground-up/).
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Unfortunately, the current method of providing protection-from-impersonation
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is terrible. Traditionally, OS and browser vendors pick a range of root
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certificates to bundle with their software - a list that's generally hundreds
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of entries long - and everyone trusts that the list is good. Anyone who can
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get a certificate into the lists can then sell certificates signed by it to
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people who can't (like me, for a start).
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They can sell certificates for any domain, for any reason, with any degree of
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publicity, transparency or validation; the only recourse vendors have is to
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threaten to stop trusting them if the're shown to be issuing certificates that
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don't meet some standard or another. If they're compromised and the key for the
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root certificate is stolen -
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[as happened in 2011](https://www.eff.org/deeplinks/2011/03/iranian-hackers-obtain-fraudulent-https)
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- then it's a mad scramble to revoke or blacklist new certificates based on that
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stolen information before too much harm is done.
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Recently, some vendors - Chrome, for instance - haver started introducing
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[certificate pinning](https://www.imperialviolet.org/2011/05/04/pinning.html)
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to restrict the range of CAs that are valid for a particular domain. This helps
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a bit against some attacks on large sites, but isn't much use as a general
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solution.
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As for the first part - the encryption itself - there's a lot of discussion
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right now over which parameters are safe, and which aren't. There's probably
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*some* setups that're safe from cryptanalysis - or if not, then we can probably
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come up with some. In this area, one more problem we have with the current CA
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model is that deploying new types of certificates is a slow process - you have
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to wait for a trusted CA to start offering them, before you can use them.
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#### Solutions
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The current system, then, can be summarised as trust silos. The main contender
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to replace it is an RFC known as
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[DANE](https://datatracker.ietf.org/doc/rfc6698/).
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This leverages DNSSEC-signed DNS to publish records that say which certificates
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(rather than certificate authorities) are valid for a particular service running
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on a domain. As it utilises the DNS, we move from trust silos to hierarchical
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trust.
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Hierarchical trust is narrower, and so better, but still vulnerable to
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compromises of keys not under your control. However, the only other schemes
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I'm really aware of at the moment are based on web-of-trust relationships with
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offline identity verification. This boils down to everyone manually curating
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bookmarks that tell them how much to trust things, and there are still keys
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out of your control that, if compromised, break you - you just get to choose
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between trust anchors more flexibly than with a hierarchical system. I'm not
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convinced the extra effort is worth it, so I've deployed DNSSEC + DANE instead,
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and in the next article, I'll go over how I did it.
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