$ apt-cache policy libssl1.0.0
libssl1.0.0:
  Installed: 1.0.2g-1ubuntu4.5
  Candidate: 1.0.2g-1ubuntu4.5
  Version table:
 *** 1.0.2g-1ubuntu4.5 100
        100 /var/lib/dpkg/status
     1.0.2g-1ubuntu4.1 500
        500 http://mirror.uoregon.edu/ubuntu xenial-updates/main amd64 Packages
        500 http://mirror.uoregon.edu/ubuntu xenial-security/main amd64 Packages
     1.0.2g-1ubuntu4 500
        500 http://mirror.uoregon.edu/ubuntu xenial/main amd64 Packages

$ apt-cache policy libssl-dev
libssl-dev:
  Installed: (none)
  Candidate: 1.0.2g-1ubuntu4.1
  Version table:
     1.0.2g-1ubuntu4.1 500
        500 http://mirror.uoregon.edu/ubuntu xenial-updates/main amd64 Packages
        500 http://mirror.uoregon.edu/ubuntu xenial-security/main amd64 Packages
     1.0.2g-1ubuntu4 500
        500 http://mirror.uoregon.edu/ubuntu xenial/main amd64 Packages

sudo apt-get install libssl1.0.0=1.0.2g-1ubuntu4.1