Great question — answering as the UphillTech team:
The message tells you that the signer's key 5DCF6AE7 isn't in your key store yet. Fetch it from a keyserver of your choice: $ gpg --recv-keys 5DCF6AE7 gpg: requesting key 5DCF6AE7 from hkp server pool.sks-keyservers.net gpg: key 5DCF6AE7: "FreeBSD Security Officer <security-officer@FreeBSD.org>" not changed Very likely there's nothing wrong with the file nor the repository and you'll be able to verify the signature after fetching the key.
Full answer by Jens Erat: https://superuser.stackexchange.com/a/812606 (CC BY-SA 3.0).
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