Conversation

Emily Stark
@estark37
a small human has been consuming all my blogging time lately, but I decided to get back into the game with a post full of terrible ideas for how to abuse Certificate Transparency to re-create public key pinning:
emilymstark.com
Certificate Transparency is really not a replacement for key pinning
I’ve noticed that there’s a common misconception that Certificate Transparency is a replacement for HTTP public key pinning. If those words make no sense to you: HTTP public key pinning was a...
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Aranjedeath
@Aranjedeath
Replying to
@estark37
and
@Cryptoki
Wondering if browser could enforce CAA list if DNS was delivered securely lol 95% of the benefits with 95% less pain over HPKP. Does not solve "My CA was breached", but helps with other CA breached/etc
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Daniel Micay
@DanielMicay
Replying to
@Aranjedeath
@estark37
and
@Cryptoki
This is provided by TLSA records, not CAA. TLSA records work well. You can use them to pin the hash of a leaf key, an intermediate key or a root key. You can have multiple valid pins which allows rotation, etc. You can set TTL low to minimize disruption from making mistakes.
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Aranjedeath
@Aranjedeath
Replying to
@DanielMicay
@estark37
and
@Cryptoki
spent 15 minutes just now trying to get one of these services to print me an appropriate DNS record, no dice. Would love for any of this to be about 10x easier for the standard use-case of having a single SSL root issuer
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Daniel Micay
@DanielMicay
Replying to
@Aranjedeath
@estark37
and
@Cryptoki
To get the public key hash: openssl x509 -in public-certificate.pem -pubkey -noout | openssl pkey -pubin -outform der | openssl dgst -sha256 -hex For leaf keys: TLSA 3 1 1 5FDBAC0BE6EE09E8B118DF22392F90CC0421EAA05993900DA27B8BE5 Change 3 to 2 for intermediate/root keys.
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Daniel Micay
@DanielMicay
Replying to
@DanielMicay
@Aranjedeath
and 2 others
It's mostly verified in practice by mail servers. To enable DANE verification for Postfix, you set up a validating resolver (unbound is nice), set that as your only resolver in /etc/resolv.conf and then enable the 2 settings to have Postfix enforce it.
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Daniel Micay
@DanielMicay
Replying to @encthenet
Enabling it for Postfix simply requires setting up unbound as your resolver and then enabling 2 configuration options: smtp_dns_support_level = dnssec smtp_tls_security_level = dane Enables opportunistic dane where it uses it when there are TLSA records and prevents downgrades.
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