Comment 30 for bug 1636573

On 16.04 LTS xenial, manually downloading and installing

http://archive.ubuntu.com/ubuntu/pool/main/p/pyopenssl/python-openssl_16.1.0-1_all.deb
http://archive.ubuntu.com/ubuntu/pool/main/p/python-cryptography/python-cryptography_1.7.1-2_amd64.deb

solved this problem for me. Because each package breaks the version of the other installed by default on 16.04 LTS xenial, the two packages must be installed _together_ with an override:

sudo dpkg -i --force-breaks python-cryptography_1.7.1-2_amd64.deb python-openssl_16.1.0-1_all.deb

In my case, I also needed to install the standard "python-setuptools" package from the standard distribution repository, after which manual configuration was necessary:

sudo dpkg --configure --force-breaks python-cryptography python-openssl