Verify your ISO download.
Windows user? Follow these instructions instead.
Once you have downloaded an ISO, verify it for security and integrity. If you downloaded your ISO via BitTorrent, the file has already been verified as part of the download process (just make sure that you got the torrent from torrent.fedoraproject.org). Otherwise, to verify your ISO, start by downloading the proper SHA1SUM file into the same directory as the ISO:
Install DVD / Rescue CD
Live Media (both GNOME and KDE)
Next, import Fedora's GPG key:
$ wget https://fedoraproject.org/static/fedora.gpg $ gpg --import fedora.gpg
Now, to verify that the SHA1SUM file is valid, make sure that it has a good signature from the key ID 4F2A6FD2.
$ gpg --verify SHA1SUM
Finally, now that the SHA1SUM file has been verified, check that the ISO's checksum matches:
$ sha1sum -c SHA1SUM
If the output states that the file is valid, you're good to go!