OCB has a clean, short, embeddable reference implemention, and there's a patent grant permitting usage in GPL projects. (Calling it "proprietary" is a stretch, but I understand what you mean.)
GCM didn't have any great implementations. There's starting to be an implementation in OpenSSL 1.0, but at the time mosh was written, that was difficult to count on, and even now that's still shaky.
It's important that the crypto algorithm implementation be known to be correct and safe (avoid side channels, etc.).
As far as I know there's no particular reason that iSSH does not use the standard mosh implementation. One thing to note is that iSSH is not free software (everything it embeds -- PuTTY, Xorg, dwm, etc. -- is under an MIT-style license), so embedding a GPL project would have forced them to open up the iSSH source code.
It would be great if someone wanted to write a free software terminal emulator for iOS, and at that point you can absolutely include mosh. (I'd probably encourage _building_ on mosh, which happens to include a rigorous terminal implementation.) But it's true that you can't embed GPL software inside proprietary software.
GCM didn't have any great implementations. There's starting to be an implementation in OpenSSL 1.0, but at the time mosh was written, that was difficult to count on, and even now that's still shaky.
It's important that the crypto algorithm implementation be known to be correct and safe (avoid side channels, etc.).
As far as I know there's no particular reason that iSSH does not use the standard mosh implementation. One thing to note is that iSSH is not free software (everything it embeds -- PuTTY, Xorg, dwm, etc. -- is under an MIT-style license), so embedding a GPL project would have forced them to open up the iSSH source code.
It would be great if someone wanted to write a free software terminal emulator for iOS, and at that point you can absolutely include mosh. (I'd probably encourage _building_ on mosh, which happens to include a rigorous terminal implementation.) But it's true that you can't embed GPL software inside proprietary software.