Add Check SSH Key Fingerprints Of Known Hosts as a Unix TIL

unix/check-ssh-key-fingerprints-of-known-hosts.md

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+# Check SSH Key Fingerprints Of Known Hosts
+
+The `ssh-keygen` utility can do a bunch of things related to SSH keys including
+generating key pairs, removing a key, and even showing the fingerprints for a
+public keys file.
+
+After [the recent GitHub SSH key
+rotation](https://github.blog/2023-03-23-we-updated-our-rsa-ssh-host-key/), I
+wanted to check that the key I had added produced a fingerprint matching what
+they described in the article.
+
+The `-l` flag will list the fingerprints and the `-f` flag allows you to
+specify what file it processes when doing that.
+
+```bash
+ssh-keygen -lf ~/.ssh/known_hosts
+```
+
+I have a bunch of known hosts, so I can narrow it down to just the GitHub entry
+like so.
+
+```bash
+ssh-keygen -lf ~/.ssh/known_hosts | grep github.com
+3072 SHA256:uNiVztksCsDhcc0u9e8BujQXVUpKZIDTMczCvj3tD2s github.com (RSA)
+```
+
+And [it matches what GitHub
+lists](https://docs.github.com/en/authentication/keeping-your-account-and-data-secure/githubs-ssh-key-fingerprints),
+so I'm good to go.
+
+See `man ssh-keygen` for more details.