Change dependency from pycrypto

[alanyee]

Is your feature request related to a problem? Please describe.
Pycrypto has not been maintained since 2014. So it susceptible to vulnerabilities like CVE-2013-7459 and CVE-2018-6594, and lacks some compatibility with the latest versions of python. Thus should not be in the tox file, documentation, etc.
Describe the solution you'd like
Replace pycrypto with an active, well-maintained python crypto library for development and testing
Describe alternatives you've considered
pycryptodome is "an almost drop-in replacement for the old PyCrypto library", but other libraries can still be considered.

[parthea]

Hi @alanyee,

I'm going to close this issue as pycrypto was removed in #799 .