2022-02-14 19:53:22 +01:00
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# OVH DANE Companion
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> Untested code ahead! This was done in a rush and isn't tested! It *should* work,
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> but I wouldn't be surprised if it breaks sometimes.
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## Aim
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I wanted to implement in a matter of a few days worth of free time a companion
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container for my Let's Encrypt container. My certificates are generated by a
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Docker container, and I wanted to deploy TLSA records automatically.
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DANE and TLSA records are used to avoid TLS downgrade attacks, such as during a
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MITM attacks.
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I also wanted to have a 100% score on internet.nl for my email server security,
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and I got [it](https://internet.nl/mail/louis-vallat.xyz/671317/).
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## Rollover scheme
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There **isn't** any. I could add a "2 1 1" record using Let's Encrypt's root certificates,
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but then I could just use permanently a "2 1 1" record and the "3 1 1" record would
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be useless.
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As I used an external container to renew the certificates, I cannot modify the
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renewal procedure, so I can't use the "current + next" rollover scheme.
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In compensation, I set the TLSA TLLs as the lowest my DNS provider allows: 60 seconds.
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In case of a key rollover, the TLSA records will be wrong for **at most** 2 minutes
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(2 TTLs just to make sure), as long as some entity on the way doesn't keep the record
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longer than the TTL specified (that can happen with lazy ISPs). TLSA records being
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borked for 2 minutes once every few months shouldn't be an issue.
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Although this is not new, maybe a bit young (from 2012), this technology isn't
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widely spread.
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2022-02-14 19:56:53 +01:00
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## Security addendum
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Although it provides a bit more security, as it prevents MITM attacks from
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downgrading your TLS (or disable it all together), I would ***strongly*** recommend
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to send sensitive emails **only** using PGP encryption! Plain text emails are
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privacy nightmares!
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2022-02-14 19:53:22 +01:00
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## References and links
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- Article from Abyss Project: [link](https://www.abyssproject.net/2016/09/creer-utiliser-enregistrements-tlsa-dane/)
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- Internet technologies tester: [link](https://internet.nl/)
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- SMTP Protection HowTo: [link](https://github.com/internetstandards/toolbox-wiki)
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- OVH API: [link](https://eu.api.ovh.com/)
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