libssh2 介绍
libssh2是一个C 函数库，用来实现SSH2协议。
主要功能：
- Key Exchange Methods : diffie-hellman-group1-sha1, diffie-hellman-group14-sha1, diffie-hellman-group-exchange-sha1
- Hostkey Types : ssh-rsa, ssh-dss
- Ciphers : aes256-cbc (rijndael-cbc@lysator.liu.se), aes192-cbc, aes128-cbc, 3des-cbc, blowfish-cbc, cast128-cbc, arcfour, none
- Compression Schemes : zlib, none
- MAC hashes : hmac-sha1, hmac-sha1-96, hmac-md5, hmac-md5-96, hmac-ripemd160 (hmac-ripemd160@openssh.com), none
- Authentication : none, password, public-key, hostbased, keyboard-interactive
- Channels : shell, exec (incl. SCP wrapper), direct-tcpip, subsystem
- Global Requests : tcpip-forward
- Channel Requests : x11, pty
- Subsystems : sftp(version 3), publickey(version 2)
- Thread-safe : just don’t share handles simultaneously
- Non-blocking : it can be used both blocking and non-blocking
- Your sockets : the app hands over the socket, calls select() etc.
- OpenSSL or gcrypt : builds with either