OpenSSH 6.x has many awesome new features such as two-factor auth with key and a password. To get this newer version on Debian Wheezy, use backports. I’ll show you how!
1. First add the following line to your /etc/apt/sources.list:
deb http://ftp.debian.org/debian/ wheezy-backports main non-free contrib
(Add this in addition to any other entries you may have in that file.)
$ sudo apt-get update
3. Next install openssh from backports
$ sudo apt-get -t wheezy-backports install openssh-server