pmeerw's blog

Mon, 02 Oct 2023

Null MX

For servers that do not accept mail, there's "null MX". See RFC 7505.

posted at: 22:09 | path: /configuration | permanent link

Tue, 16 May 2023

DNS, minimal ANY queries

RFC 8482 deprecates DNS ANY queries. These were mostly used for debugging, i.e. retrieving all information for a domain. DNS server now just respond with HINFO "RFC8482" "" in the CPU and OS field of the HINFO response to indicate that information has been suppressed.

See also Cloudflare blog on this topic.

And the (hard to come by) configuration for bind9 is (tada!): 

minimal-any yes;
Use dig +tcp to get a full response (see here).

posted at: 10:24 | path: /configuration | permanent link

Sat, 17 Dec 2022

Using DNS to securely publish SSH key fingerprints

Another nice article showing off DNSSEC strength...

Generate SSHFP DNS records for by host (pmeerw.net): 

$ ssh-keygen -r @
@ IN SSHFP 1 1 3b00267ed86c211026e6d8b8eb5d9a7d9e51cf7d
@ IN SSHFP 1 2 189d464e8a13d2df66d882afdcb4220fb281ba1f19eda96aa35bf1a50188b0a7
@ IN SSHFP 2 1 adb06e3c4de279d2338bbec35a9a64c8661fb431
@ IN SSHFP 2 2 50e72d460ea86ad416b74b71f9b0c948bf42004ebf730290eff9d43fea9545a6
@ IN SSHFP 3 1 aaa45514f6bd534448ab7f09842fe1e13c269142
@ IN SSHFP 3 2 cc68f391aea002966cc3d7e84ce41dc73d4cfb6c2381e5b665f26603f8317dd3
@ IN SSHFP 4 1 7482ed5e3e6621978bd0bbd61f6b9740dcef252c
@ IN SSHFP 4 2 eb77b6f29bee067d6524459e4cfc696881bd70908d514be682cb068746729594

SSH can silently connect to an SSH server (without asking to verify the host fingerprint!) if VerifyHostKeyDNS is enabled: ssh -o VerifyHostKeyDNS=yes pmeerw@pmeerw.net.

posted at: 22:58 | path: /configuration | permanent link

PGP Key Distribution via DNSSEC: OPENPGPKEY

RFC7929 describes a way to put OpenPGP public keys into DNS using DANE. Here's an article which I shamelessly condense here...

There is a DNS resource record that stores the complete public key. I'm using ECC to bring down key size. It looks like this: 

c746aa6d791946caf1aade6dc6c5e720e6e79d650e5b882dc11a2078._openpgpkey.pmeerw.net. IN OPENPGPKEY (
                  mDMEY54vtRYJKwYBBAHaRw8BAQdAmhK78RNv+Azsrrcgnb4Ijf4JwEOfHM8D
                  paY2yy1w0oG0KlBldGVyIE1lZXJ3YWxkLVN0YWRsZXIgPHBtZWVyd0BwbWVl
                  cncubmV0PoiQBBMWCAA4FiEE5u5nS8lBNCYy5igrw5J6UWK+XtEFAmOeL7UC
                  GwMFCwkIBwIGFQoJCAsCBBYCAwECHgECF4AACgkQw5J6UWK+XtE+dAD/dZAp
                  If2WWK2fAQgGIxOepBr6Nj2g6Z78W25wyYiSxvIA/1VtCuCsveRGmKZ0wnuQ
                  kJP4z3v+r/XdjRJeingYSnsKuDgEY54vtRIKKwYBBAGXVQEFAQEHQPCrzg3G
                  IRhYWFdUkps1DSqmLEZ5xQX6D96jYpq28Lp1AwEIB4h4BBgWCAAgFiEE5u5n
                  S8lBNCYy5igrw5J6UWK+XtEFAmOeL7UCGwwACgkQw5J6UWK+XtGQyQD/RD1d
                  zIk/Kjnb1yKcW+GAIHkpahgEQzpk7Bcxk38ReaAA/j2ZoXGMeMNVlJdOIv7d
                  gr/Hw9ygwxInPg9Nth2wpKoB
)
The name part is the SHA-256 hash of "pmeerw". You can use the command openpgpkey --create pmeerw@pmeerw.net to create the record (install the Debian/Ubuntu hash-slinger package).

Try openpgpkey.info to query a PGP public key!

posted at: 22:49 | path: /configuration | permanent link

Sat, 17 Sep 2022

Open Graph meta tags

Open Graph meta tags allow a web page to be interpreted/rendered nicely by social media platform, such as Twitter, Facebook (who originally created it), etc. It's as simple as putting some <meta property="og:xxx" content="..."/> in the <head> of an HTML page, where xxx can be title, type, description, image, etc.

https://www.opengraph.xyz is really useful for checking, previewing and generating Open Graph meta tags, thanks to Duncan for pointing out!

Another proposal to add information to web pages is JSON for Linking Data (JSON-LD). Here the focus is on machine-readable meta data for a person, place, event, product, recipe, etc. Yet another is Twitter Cards.

posted at: 22:05 | path: /configuration | permanent link

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