I had the same problem on my Mac when installing with pip. I then removed pycrypto and installed it again with easy_install, like this:

pip uninstall pycryptoeasy_install pycrypto

also as Luke commented: If you have trouble running these commands, be sure to run them as admin (sudo)

Hope this helps!

EDIT: As winklerr correctly notes above, pycrypto is no longer safe. Use pycryptodome instead, it is a drop-in replacement

I ran into this on Mac as well, and it seems to be related to having an unfortunately similarly named "crypto" module (not sure what that is for) installed alongside of pycrypto via pip.

The fix seems to be removing both crypto and pycrypto with pip:

sudo pip uninstall cryptosudo pip uninstall pycrypto

and reinstalling pycrypto:

sudo pip install pycrypto

Now it works as expected when I do something like:

from Crypto.Cipher import AES

WARNING: Don't use crypto or pycrypto anymore!

As you can read on this page, the usage of pycrypto is not safe anymore:

Pycrypto is vulnerable to a heap-based buffer overflow in the ALGnew function in block_templace.c. It allows remote attackers to execute arbitrary code in the python application. It was assigned the CVE-2013-7459 number.

Pycrypto didn’t release any fix to that vulnerability and no commit was made to the project since Jun 20, 2014.

Update 2021-01-18

The CVE is fixed now (thanks @SumitBadsara for pointing it out!). You can find the current status of the open security tickets for each package at the Debian security tracker:

• python-crypto
• pycryptodome

Use Python3's pycryptodome instead!

Make sure to uninstall all versions of crypto and pycrypto first, then install pycryptodome:

pip3 uninstall crypto pip3 uninstall pycrypto pip3 install pycryptodome

All of these three packages get installed to the same folder, named Crypto. Installing different packages under the same folder name can be a common source for errors!

For more information, see pycryptodome.org.

Best practice: virtual environments

In order to avoid problems with pip packages in different versions or packages that install under the same folder (i.e. pycrypto and pycryptodome) you can make use of a so called virtual environment. There, the installed pip packages can be managed for every single project individually.

To install a virtual environment and setup everything, use the following commands:

# install python3 and pip3sudo apt updatesudo apt upgradesudo apt install python3sudo apt install python3-pip# install virtualenvpip3 install virtualenv# install and create a virtual environment in your target foldermkdir target_foldercd target_folderpython3 -m virtualenv .# now activate your venv and install pycryptodomesource bin/activatepip3 install pycryptodome# check if everything worked: # start the interactive python console and import the Crypto module# when there is no import error then it workedpython>>> from Crypto.Cipher import AES>>> exit()# don't forget to deactivate your venv againdeactivate

For more information, see docs.python-guide.org.