I'd like to "up" this discussion, because I also noticed that the library is very slow.
I haven't been able to manage why.
In my case, I have an Sftp server that I don't managed (provided by my hosting service). It uses aes256-ctr for its session encryption.
I've tested downloads from this server, with 3 applications, FlashFXP, FileZilla, and mine which uses this library.
With FlashFXP and FileZilla files are transfered at an average of 500KB/s, in my app i'm stuck at 75KB/s.
I though that may be the library was using another encryption (a slower one), but the CurrentServerEncryption is aes256-ctr like the other one.
I don't know if I can change the connection encryption (may be the server can handle another type of encryption), and if I can, how ?
But it seems weird that for the same encryption the library is about 10 times slower.
Anyway, thank you very much for the library, I'm trying to figure out how to fix this myself, but I'm not good enough with encryption ^^