Ben Laurie blathering

Trust and Vulnerability

Ed Felten has a nice post about the crazy idea that someone can decide for us which CAs are trusted. He correctly points out that we conflate two meanings of the word “trust”, but then proposes to fix it by using the word slightly differently, for example:

“CNNIC is a trusted certificate authority.”


“Everyone trusts CNNIC to be a certificate authority.”

I’ve long advocated instead saying “is vulnerable to”, which makes it much clearer what is going on, so I would say “CNNIC is a certificate authority everyone is vulnerable to”. “Trusted third party” would become “Third party you are vulnerable to” and so on. Kinda clunky, but you know where you stand.

A historical note: I believe I came up with this in one of my very first conversations with Jon Shapiro and Mark Miller about the nature of “trust” in distributed computer systems – a word that really should not be used at all in that context, I believe.


  1. Also – reliance and betrayal.

    “Philosophers such as Annette Baier have made a difference between trust and reliance by saying that trust can be betrayed, whilst reliance can only be disappointed (Baier 1986, 235)”

    Baier, Annette (1986). Trust and Antitrust. Ethics 96(2): 231-260.

    Comment by Terrell — 25 Feb 2010 @ 18:06

  2. In some ways its like a TCB, to quote wikipedia’s article on it:

    “In other words, the trusted computing base is ‘trusted’ first and foremost in the sense that it has to be trusted, and not necessarily that it is trustworthy.”

    That said, I guess it is all one of degrees anyway. You’re trusting the code in Firefox to actually validate the certificates correct, and the TLS protocol to operate properly, and your computer to not have a rootkit on it when shipped from the manufacturer, etc.

    Lots of trust issues to go around, I don’t know that CAs are really the weakest link.

    Comment by Andy Steingruebl — 25 Feb 2010 @ 18:07

  3. Like Goldman Sachs was a trusted bank.

    Comment by ignisvulpis — 25 Feb 2010 @ 22:46

  4. Vulnerability-to and trust are distinct relations, both of which have explanatory power. Rather than banishing one in favor of the other, I think we should use both, and be clear about which one we mean in a given case.

    Comment by Ed Felten — 1 Mar 2010 @ 15:45

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