### Error: "You have not agreed to the Xcode license agreements"

On macOS, did you try to install the dependencies with pip and encounter the following error?

```
Downloading cffi-1.9.1.tar.gz (407kB): 407kB downloaded
  Running setup.py (path:/private/tmp/pip_build_root/cffi/setup.py) egg_info for package cffi

You have not agreed to the Xcode license agreements, please run 'xcodebuild -license' (for user-level acceptance) or 'sudo xcodebuild -license' (for system-wide acceptance) from within a Terminal window to review and agree to the Xcode license agreements.

    No working compiler found, or bogus compiler options
    passed to the compiler from Python's distutils module.
    See the error messages above.
    (If they are about -mno-fused-madd and you are on OS/X 10.8,
    see http://stackoverflow.com/questions/22313407/ .)

----------------------------------------
Cleaning up...
Command python setup.py egg_info failed with error code 1 in /private/tmp/pip_build_root/cffi
Storing debug log for failure in /Users/algore/Library/Logs/pip.log
```

The Xcode compiler is installed but requires you to accept its license agreement prior to using it. Run `xcodebuild -license` to agree and then retry installing the dependencies.

### Error: "fatal error: 'openssl/opensslv.h' file not found"

On macOS, did you try to install pycrypto and encounter the following error?

```
build/temp.macosx-10.12-intel-2.7/_openssl.c:434:10: fatal error: 'openssl/opensslv.h' file not found

#include <openssl/opensslv.h>

        ^

1 error generated.

error: command 'cc' failed with exit status 1

----------------------------------------
Cleaning up...
Command /usr/bin/python -c "import setuptools, tokenize;__file__='/private/tmp/pip_build_root/cryptography/setup.py';exec(compile(getattr(tokenize, 'open', open)(__file__).read().replace('\r\n', '\n'), __file__, 'exec'))" install --record /tmp/pip-sREEE5-record/install-record.txt --single-version-externally-managed --compile failed with error code 1 in /private/tmp/pip_build_root/cryptography
Storing debug log for failure in /Users/algore/Library/Logs/pip.log
```

You are running an old version of `pip` that cannot build the `pycrypto` dependency. Upgrade to a new version of `pip` by running `sudo pip install -U pip`.

### Various parts of the internet appear to be offline through the VPN

The issue may related to the MTU size, try to use `ping` with the don't fragment bit and various packet size in order to determine the MTU size for your network and set up this properly on the physical adapter.