OpenSSH 6.7 disabled by default insecure ciphers. Unfortunately, the ssh client in QtCreator only supports 3des-cbc and aes128-cbc. These ciphers are no longer enabled by default, and thus QtCreator cannot connect to newer SSH servers.

See these release notes for more information:
http://www.openssh.com/txt/release-6.7

You either need to implement a CTR-mode cipher, or ChaCha. It looks like recent Botan versions support both, though I'm not sure about Poly1305:
http://botan.randombit.net/doxygen/classBotan_1_1ChaCha.html
http://botan.randombit.net/doxygen/classBotan_1_1CTR__BE.html

This affects all versions.