M2Crypto is required.

M2Crypto is required to create the signature string and verify if it is
valid or not.

setup.py

@@ -24,6 +24,7 @@ setup(
     keywords="slapos networkcache shadir shacache",
     install_requires=[
       'setuptools', # for namespace
+      'M2Crypto',
     ],
     classifiers=[
       'Development Status :: 4 - Beta',