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> "croc send -c 'xyz blahblahblah' filename" on multiple computers without error That seemed to be a bug and is fixed now. After two parties enter a channel it

by qrv3w 6y ago

> "croc send -c 'xyz blahblahblah' filename" on multiple computers without error That seemed to be a bug and is fixed now. After two parties enter a channel it should give you a "room is full" response. > Magic Wormhole works a bit differently. IIRC it dynamically requests a channel from the server which is prepended to the passphrase as a number. This seems a bit more resilient to me, as the birthday problem suggests it's quite likely two people will end up with the same channel just by bad luck with Croc....There are only ~900 different three letter word beginnings in the wordlist, so you'd only need to claim that many channels on the server to make it unusable for anyone who lets Croc pick passwords, and occasional collisions between users are certain. Lol that should probably be fixed. I think wormhole uses only 99 channels [1] so it is also susceptible to a DOS attack. But generally, collisions in channels can occur but are probably pretty rare because I don't have enough people using croc simultaneously to collide. Importantly - colliding channels doesn't undermine security because you have to have the whole passphrase to successfully perform PAKE. But, when you say it should probably be fixed, you refer to mitigating a DOS attack? [1]: https://github.com/warner/magic-wormhole/issues/107 https://github.com/warner/magic-wormhole/issues/107

bscphil 6y ago
> That seemed to be a bug and is fixed now. That's likely the case, it looks like I had an old version installed in Termux. But in any event that's just a matter of getting an intelligible error message, and not fixing the underlying problem. > I think wormhole uses only 99 channels [1] so it is also susceptible to a DOS attack. In that case I'd certainly have the same concern. > But generally, collisions in channels can occur but are probably pretty rare because I don't have enough people using croc simultaneously to collide. I disagree. Suppose you only average 2 users at a time. In this case ~1/630 connections will randomly collide, just by chance, which means that some people have certainly experienced this already. IMO that's too high, and in any case the relay code certainly shouldn't be written to only support <10 channels. (Note that the number of collisions will actually be higher than my back of the envelope math suggests, because some 3 character prefixes will be more common than others since you're using English words.) Importantly - Wormhole doesn't have this problem, even though it technically has a lower channel limit, because it allocates channels dynamically instead of having the client pick them. IMO it's also pretty weird to take the channel ID from the beginning of the passphrase. This takes away any entropy you'd otherwise get from the first word, since you're using a wordlist, which means the effective size of the secret used for PAKE is only about 1600^2. If you're okay with that, just use the entire word. It seems pretty low to me. But yes I would like to see more work done to mitigate extremely easy DOS attacks, given that this seems like the most obvious vulnerability to these relay-managed PAKE approaches.
- qrv3w 6y ago
  I'm confused about why you wrote "relay code shouldn't be written to only support <10 channels" as any three character combination is a channel? You mention wormhole doesn't have a problem with colliding channels, but that it requires assigning a channel from the relay. To me this is a trade-off. If wormhole can't connect to a relay, wormhole can't assign a channel and won't work. Whereas, in croc, if you can't connect to the relay it will still work over LAN since the client chooses the channel. I appreciate this discussion, there's a discussion on Github about this now. [1] Would you mind moving this discussion there? [1]: https://github.com/schollz/croc/issues/261 https://github.com/schollz/croc/issues/261
psanford 6y ago
You are wrong about a 99 channel limit. You can see that is not the case by passing the `--code` flag to wormhole and specifying a mailbox id larger than 100.

by qrv3w 6y ago

bscphil 6y ago

> That seemed to be a bug and is fixed now. That's likely the case, it looks like I had an old version installed in Termux. But in any event that's just a matter of getting an intelligible error message, and not fixing the underlying problem. > I think wormhole uses only 99 channels [1] so it is also susceptible to a DOS attack. In that case I'd certainly have the same concern. > But generally, collisions in channels can occur but are probably pretty rare because I don't have enough people using croc simultaneously to collide. I disagree. Suppose you only average 2 users at a time. In this case ~1/630 connections will randomly collide, just by chance, which means that some people have certainly experienced this already. IMO that's too high, and in any case the relay code certainly shouldn't be written to only support <10 channels. (Note that the number of collisions will actually be higher than my back of the envelope math suggests, because some 3 character prefixes will be more common than others since you're using English words.) Importantly - Wormhole doesn't have this problem, even though it technically has a lower channel limit, because it allocates channels dynamically instead of having the client pick them. IMO it's also pretty weird to take the channel ID from the beginning of the passphrase. This takes away any entropy you'd otherwise get from the first word, since you're using a wordlist, which means the effective size of the secret used for PAKE is only about 1600^2. If you're okay with that, just use the entire word. It seems pretty low to me. But yes I would like to see more work done to mitigate extremely easy DOS attacks, given that this seems like the most obvious vulnerability to these relay-managed PAKE approaches.

qrv3w 6y ago
I'm confused about why you wrote "relay code shouldn't be written to only support <10 channels" as any three character combination is a channel? You mention wormhole doesn't have a problem with colliding channels, but that it requires assigning a channel from the relay. To me this is a trade-off. If wormhole can't connect to a relay, wormhole can't assign a channel and won't work. Whereas, in croc, if you can't connect to the relay it will still work over LAN since the client chooses the channel. I appreciate this discussion, there's a discussion on Github about this now. [1] Would you mind moving this discussion there? [1]: https://github.com/schollz/croc/issues/261 https://github.com/schollz/croc/issues/261

psanford 6y ago

You are wrong about a 99 channel limit. You can see that is not the case by passing the `--code` flag to wormhole and specifying a mailbox id larger than 100.