--- a/setup.py	2019-07-22 20:18:46.000000000 +0200

+++ b/setup.py	2019-08-01 21:49:28.107607851 +0200

@@ -238,7 +238,7 @@

     install_requires=[

         'six>=1.11.0',       # MIT license

         'txaio>=18.8.1',     # MIT license

-        'cryptography>=2.7', # BSD *or* Apache license

+        'cryptography>=2.6.1', # BSD *or* Apache license

     ],

     extras_require={

         'all': extras_require_all,