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| -rw-r--r-- | doc/todo/multicast___34__broadcasting__34___of_content_on_local_net/comment_1_5353dc46ccecc6077f2643d281d58f99._comment | 91 |
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diff --git a/doc/todo/multicast___34__broadcasting__34___of_content_on_local_net/comment_1_5353dc46ccecc6077f2643d281d58f99._comment b/doc/todo/multicast___34__broadcasting__34___of_content_on_local_net/comment_1_5353dc46ccecc6077f2643d281d58f99._comment new file mode 100644 index 000000000..5c932cbf9 --- /dev/null +++ b/doc/todo/multicast___34__broadcasting__34___of_content_on_local_net/comment_1_5353dc46ccecc6077f2643d281d58f99._comment @@ -0,0 +1,91 @@ +[[!comment format=mdwn + username="joey" + subject="""comment 1""" + date="2017-03-30T16:51:24Z" + content=""" +Using a remote for this seems problimatic, because the remote is not +pointing at a single well-defined data store, but instead whatever peers +happen to exist on the network. + +For one, `copy --to=udp-multicast` would not try to send files that it thinks +are already located in that remote. I suppose this could be dealt with by +making the transfers always seem to fail, so it never thinks that the +multicast remote has any files. + +But then, `copy --from=udp-multicast` would not try to receive files, +unless it thinks they're in that remote. And we just established it should +not think any files are in that remote. So that's a problem. + +Also, the copy from/to would need to be operating on the same file at the +same time, which seems problimatic. If a receiving git-annex is a little +slower than the sender, or is operating on a slightly different set of +files, it would then miss a file being broadcast by the sender. + +These issues seem to point to this needing to use some other, more +special-purpose commands for muticast. + +---- + +It probably needs encryption, both for privacy and to ensure that files +are being received from the sender you intended, and not someone else +who might be broadcasting the contents of a different repository. + +Here's how to set up encryption and authentication with uftp, +so that both client and server actually encrypt and check that they're +talking with a known entity. It took a while to figure out. + +Client: + + uftp_keymgt -g rsa:512 ~/client_key + # Parse the fingerprint value from its output; does not + # seem to be a better way, except perhaps using openssl to examine + # the key file. This is CLIENT_FINGERPRINT + + # Pick a UID for the client. This is an 8-diget hex number, + # which needs to be unique across clients. Default is based on IP + # adddres, but for git-annex it could be derived from the git-annex + # UUID. This is CLIENT_UID. + +Server: + + uftp_keymgt -g rsa:512 ~/servant_key + # Parse the SERVER_FINGERPRINT from its output. + + # Pick a SERVER_UID for the server. + +Client: + + # create a file "authlist" that contains "$SERVER_UID|$SERVER_FINGERPRINT" + + uftpd -E -d -D/tmp/xx -k ~/client_key -U $CLIENT_UID -S '@authlist' + +Server: + + # create file "authlist" that contains "$CLIENT_UID|$CLIENT_FINGERPRINT" + # lines for each allowed client + + uftp -c -Y aes256-cbc -h sha1 -k ~/server_key -U $SERVER_UID -H '@authlist' file_to_send + +---- + +Notice that the client and server UID and key generation steps above +are the same. So, a command like `git annex multicast --gen-address` +could be run on both the server and clients, and could store +the addresses in the git-annex branch. +The uftp authlist file would be derived from all known such addresses. + +(Unlike `p2p --gen-address`, where the address allows connecting with +and authentication with a remote over TOR, these multicast addresses +are safe to make public.) + +The process of setting up a multicast classroom would then be: + +1. Teacher runs `git annex multicast --gen-address; git annex sync` +2. Students each run `git annex multicast --gen-address; git annex sync` +3. Teacher runs `git annex sync` once all the students have generated addresses. + (Now the students all have received the teacher's address, and the teacher + has received all the student's addresses.) +4. Students each run `git annex multicast-receive`, which listens for + files going by and stores them. +5. Once the students are listening (*ahem*), teacher runs + `git annex multicast-send [file]` to distribute files. |