add encryption warning

Remote/GitLFS.hs

@@ -12,6 +12,7 @@ import Types.Remote
 import Annex.Url
 import Types.Key
 import Types.Creds
+import qualified Annex
 import qualified Git
 import qualified Git.Types as Git
 import qualified Git.Url
@@ -108,11 +109,21 @@ mySetup _ mu _ c gc = do
 
 	let repo = fromMaybe (giveup "Specify url=") $
 		M.lookup "url" c
-	-- TODO: don't allow using encryption w/o the user indicating they
-	-- know it will only encrypt git-annex objects, not git pushes
-	-- TODO: don't allow using encryption=shared w/o the user
-	-- indicating that pushing to the git-lfs remote will expose the
-	-- encrypted data.
+	
+	when (isEncrypted c) $
+		unlessM (Annex.getState Annex.force) $
+			giveup $ unwords $
+				[ "You asked that encryption be enabled for"
+				, "this remote, but only the files that"
+				, "git-annex stores on it would be encrypted;"
+				, "anything that git push sends to it would"
+				, "not be encrypted. Even encryption=shared"
+				, "encryption keys will be stored on the"
+				, "remote for anyone who can access it to"
+				, "see."
+				, "(Use --force if you want to use this"
+				, "likely insecure configuration.)"
+				]
 	(c', _encsetup) <- encryptionSetup c gc
 
 	-- The repo is not stored in the remote log, because the same

doc/special_remotes/git-lfs.mdwn

@@ -41,11 +41,12 @@ store its SHA256 checksum in the git-annex branch.
 
 ## encryption notes
 
-The encryption= parameter only makes git-annex encrypt data stored on the
-remote. `git push` can also be used with the remote (it is a git repository
-after all), and data pushed to it with git will *not* be encrypted.
+The encryption= parameter only makes git-annex encrypt data it stores
+on the remote. `git push` can also be used with the remote
+(it is a git repository after all), and data pushed to it with
+git will *not* be encrypted.
 
-This makes using encryption=shared with a git-lfs special remote very
+Using encryption=shared with a git-lfs special remote is especially
 unlikely to be secure, because the encryption key is committed to the git
 repository. It would only make sense if you never pushed it to the
 remote, or trusted the remote's host to keep it secure.