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

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://crafty-builder-6996.ck.page/e169c61186).
 
-_1292 TILs and counting..._
+_1293 TILs and counting..._
 
 ---
 
@@ -1219,6 +1219,7 @@ _1292 TILs and counting..._
 - [Change To That New Directory](unix/change-to-that-new-directory.md)
 - [Check If A Port Is In Use](unix/check-if-a-port-is-in-use.md)
 - [Check If Command Is Executable Before Using](unix/check-if-command-is-executable-before-using.md)
+- [Check SSH Key Fingerprints Of Known Hosts](unix/check-ssh-key-fingerprints-of-known-hosts.md)
 - [Check The Current Working Directory](unix/check-the-current-working-directory.md)
 - [Clear The Screen](unix/clear-the-screen.md)
 - [Command Line Length Limitations](unix/command-line-length-limitations.md)

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

@@ -0,0 +1,31 @@
+# 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.