PuTTY wish mosh

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Several people have asked us to extend PuTTY to add compatibility with Mosh, a rather unusual remote-terminal application that's particularly suited to use over bad networks. This is a tempting idea in principle, but there are several practical problems:

• The State Synchronization Protocol used by Mosh doesn't seem to have any public documentation. This makes writing another implementation difficult.
• Unlike all the protocols currently supported by PuTTY, Mosh doesn't transport a terminal stream but updates the screen by other means, so it would need hooks into the middle of the current monolithic terminal emulator. That would be a fairly large amount of work.
• Similarly, Mosh's use of the network is very different from all our existing backends, which use small numbers of TCP connections.
• On the other hand, Mosh does require an SSH client implementation for authentication and key-exchange, so there are some major parts of PuTTY that could be re-used.
• Mosh uses OCB, which is patented in the USA. While there are fairly generous licences available for the relevant patents, these are not as generous as PuTTY's copyright licence, so they would forbid uses of PuTTY's code that are currently allowed (specifically in proprietary software in military use).

It's possible that someone could write a patch to add Mosh compatibility to PuTTY that we'd be willing to accept, but it's not the most likely thing ever.