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I'm just not sure that I can see a world where all devices that rely on TLS/PKI are capable of CT SCT validation. Look at the issues we have around stale root stores still happening when we have validity periods of literally decades. Some of these clients out there simply won't ever be able to keep their trusted log store updated.

Refs: Part 1: https://scotthelme.co.uk/impending-doom-root-ca-expiring-leg... Part 2: https://scotthelme.co.uk/complexities-chain-building-ca-infr... Part 3: https://scotthelme.co.uk/cross-signing-alternate-trust-paths... Part 4: https://scotthelme.co.uk/building-certificate-chains/

There's also the Let's Encrypt root migration that was postponed due to legacy devices: https://scotthelme.co.uk/lets-encrypt-postpone-isrg-root-tra...

by akerl_8 hours ago|

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Similarly to vaccines, part of the magic is that you don't need "all", you just need "most".

Right now CT support is rough for things outside of browsers; it's a pretty fair bet that if you pick up a command line tool or library, it is not checking SCTs, and that makes those workflows vulnerable. If we flipped that, and the average command line tool or library did validate by default, it would dramatically alter the risk calculus for attackers.

by Scott_Helme_7 hours ago|

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For a scenario like this it doesn't help a given client what % of the ecosystem does SCT validation or not, all that matters is whether that client does it.

I agree that more SCT validation across the ecosystem reduces the value of a mis-issued certificate to an attacker, but a lot of value still remains.

If 90% of clients did SCT validation, an attacker can still succeed against the 10% that don't, there's no herd immunity.

by lelandbatey7 hours ago|

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You said:

> In a world [where] CT logs and CAA records [exist]

And we are in that world. CT logs and CAA records exist. They are around. What you are implying you said is:

> In a world with CT logs and CAA records [and everyone/everything reads and validates them]

We are not in that world, and we probably won't enter that world for the next 15 to 20 years because we are also in a world where folks expect networked devices to be able to communicate (mostly) securely without constantly communicating with a centralized set of clearinghouses arbitrating "what is secure".

As we are discovering, our flawed systems may need broader rethinking, especially if we want secure communication (with all the epistemological ball of yarn that comes with it) without constant total centralization, which seems to be the approach-of-least-resistance lately.