Prompt airgap to update

VERIFY_ISO.md

@@ -0,0 +1,51 @@
+### 2.3.50 ISO image built on 2021/04/26
+
+
+### Download and Verify
+
+2.3.50 ISO image:  
+https://download.securityonion.net/file/securityonion/securityonion-2.3.50.iso
+
+MD5: 1FF774520D3B1323D83BBF90BD9EFACE  
+SHA1: 0F323335459A11850B68BB82E062F581225303EE  
+SHA256: 2AACD535E0EACE17E8DC7B560353D43111A287C59C23827612B720D742DFD994 
+
+Signature for ISO image:  
+https://github.com/Security-Onion-Solutions/securityonion/raw/master/sigs/securityonion-2.3.50.iso.sig
+
+Signing key:  
+https://raw.githubusercontent.com/Security-Onion-Solutions/securityonion/master/KEYS  
+
+For example, here are the steps you can use on most Linux distributions to download and verify our Security Onion ISO image.
+
+Download and import the signing key:  
+```
+wget https://raw.githubusercontent.com/Security-Onion-Solutions/securityonion/master/KEYS -O - | gpg --import -  
+```
+
+Download the signature file for the ISO:  
+```
+wget https://github.com/Security-Onion-Solutions/securityonion/raw/master/sigs/securityonion-2.3.50.iso.sig
+```
+
+Download the ISO image:  
+```
+wget https://download.securityonion.net/file/securityonion/securityonion-2.3.50.iso
+```
+
+Verify the downloaded ISO image using the signature file:  
+```
+gpg --verify securityonion-2.3.50.iso.sig securityonion-2.3.50.iso
+```
+
+The output should show "Good signature" and the Primary key fingerprint should match what's shown below:
+```
+gpg: Signature made Mon 26 Apr 2021 03:54:51 PM EDT using RSA key ID FE507013
+gpg: Good signature from "Security Onion Solutions, LLC <info@securityonionsolutions.com>"
+gpg: WARNING: This key is not certified with a trusted signature!
+gpg:          There is no indication that the signature belongs to the owner.
+Primary key fingerprint: C804 A93D 36BE 0C73 3EA1  9644 7C10 60B7 FE50 7013
+```
+
+Once you've verified the ISO image, you're ready to proceed to our Installation guide:  
+https://docs.securityonion.net/en/2.3/installation.html