Ошибка при установке скрапа

Я пытаюсь установить scrapy, выдает следующую ошибку:

Downloading/unpacking cryptography>=0.2.1 (from pyOpenSSL->Scrapy)
  Running setup.py egg_info for package cryptography
    Package libffi was not found in the pkg-config search path.
    Perhaps you should add the directory containing `libffi.pc'
    to the PKG_CONFIG_PATH environment variable
    No package 'libffi' found
    Package libffi was not found in the pkg-config search path.
    Perhaps you should add the directory containing `libffi.pc'
    to the PKG_CONFIG_PATH environment variable
    No package 'libffi' found
    Package libffi was not found in the pkg-config search path.
    Perhaps you should add the directory containing `libffi.pc'
    to the PKG_CONFIG_PATH environment variable
    No package 'libffi' found
    Package libffi was not found in the pkg-config search path.
    Perhaps you should add the directory containing `libffi.pc'
    to the PKG_CONFIG_PATH environment variable
    No package 'libffi' found
    Package libffi was not found in the pkg-config search path.
    Perhaps you should add the directory containing `libffi.pc'
    to the PKG_CONFIG_PATH environment variable
    No package 'libffi' found
    c/_cffi_backend.c:13:17: fatal error: ffi.h: No such file or directory
    compilation terminated.
    Traceback (most recent call last):
      File "<string>", line 14, in <module>
      File "/home/nilesh/build/cryptography/setup.py", line 174, in <module>
        "test": PyTest,
      File "/usr/lib/python2.7/distutils/core.py", line 112, in setup
        _setup_distribution = dist = klass(attrs)
      File "/usr/lib/python2.7/dist-packages/setuptools/dist.py", line 221, in __init__
        self.fetch_build_eggs(attrs.pop('setup_requires'))
      File "/usr/lib/python2.7/dist-packages/setuptools/dist.py", line 245, in fetch_build_eggs
        parse_requirements(requires), installer=self.fetch_build_egg
      File "/usr/lib/python2.7/dist-packages/pkg_resources.py", line 576, in resolve
        dist = best[req.key] = env.best_match(req, self, installer)
      File "/usr/lib/python2.7/dist-packages/pkg_resources.py", line 821, in best_match
        return self.obtain(req, installer) # try and download/install
      File "/usr/lib/python2.7/dist-packages/pkg_resources.py", line 833, in obtain
        return installer(requirement)
      File "/usr/lib/python2.7/dist-packages/setuptools/dist.py", line 294, in fetch_build_egg
        return cmd.easy_install(req)
      File "/usr/lib/python2.7/dist-packages/setuptools/command/easy_install.py", line 608, in easy_install
        return self.install_item(spec, dist.location, tmpdir, deps)
      File "/usr/lib/python2.7/dist-packages/setuptools/command/easy_install.py", line 638, in install_item
        dists = self.install_eggs(spec, download, tmpdir)
      File "/usr/lib/python2.7/dist-packages/setuptools/command/easy_install.py", line 828, in install_eggs
        return self.build_and_install(setup_script, setup_base)
      File "/usr/lib/python2.7/dist-packages/setuptools/command/easy_install.py", line 1105, in build_and_install
        self.run_setup(setup_script, setup_base, args)
      File "/usr/lib/python2.7/dist-packages/setuptools/command/easy_install.py", line 1096, in run_setup
        raise DistutilsError("Setup script exited with %s" % (v.args[0],))
    distutils.errors.DistutilsError: Setup script exited with error: command 'gcc' failed with exit status 1
    Complete output from command python setup.py egg_info:
    Package libffi was not found in the pkg-config search path.

Perhaps you should add the directory containing `libffi.pc'

to the PKG_CONFIG_PATH environment variable

No package 'libffi' found

Package libffi was not found in the pkg-config search path.

Perhaps you should add the directory containing `libffi.pc'

to the PKG_CONFIG_PATH environment variable

No package 'libffi' found

Package libffi was not found in the pkg-config search path.

Perhaps you should add the directory containing `libffi.pc'

to the PKG_CONFIG_PATH environment variable

No package 'libffi' found

Package libffi was not found in the pkg-config search path.

Perhaps you should add the directory containing `libffi.pc'

to the PKG_CONFIG_PATH environment variable

No package 'libffi' found

Package libffi was not found in the pkg-config search path.

Perhaps you should add the directory containing `libffi.pc'

to the PKG_CONFIG_PATH environment variable

No package 'libffi' found

c/_cffi_backend.c:13:17: fatal error: ffi.h: No such file or directory

compilation terminated.

Traceback (most recent call last):

  File "<string>", line 14, in <module>

  File "/home/nilesh/build/cryptography/setup.py", line 174, in <module>

    "test": PyTest,

  File "/usr/lib/python2.7/distutils/core.py", line 112, in setup

    _setup_distribution = dist = klass(attrs)

  File "/usr/lib/python2.7/dist-packages/setuptools/dist.py", line 221, in __init__

    self.fetch_build_eggs(attrs.pop('setup_requires'))

  File "/usr/lib/python2.7/dist-packages/setuptools/dist.py", line 245, in fetch_build_eggs

    parse_requirements(requires), installer=self.fetch_build_egg

  File "/usr/lib/python2.7/dist-packages/pkg_resources.py", line 576, in resolve

    dist = best[req.key] = env.best_match(req, self, installer)

  File "/usr/lib/python2.7/dist-packages/pkg_resources.py", line 821, in best_match

    return self.obtain(req, installer) # try and download/install

  File "/usr/lib/python2.7/dist-packages/pkg_resources.py", line 833, in obtain

    return installer(requirement)

  File "/usr/lib/python2.7/dist-packages/setuptools/dist.py", line 294, in fetch_build_egg

    return cmd.easy_install(req)

  File "/usr/lib/python2.7/dist-packages/setuptools/command/easy_install.py", line 608, in easy_install

    return self.install_item(spec, dist.location, tmpdir, deps)

  File "/usr/lib/python2.7/dist-packages/setuptools/command/easy_install.py", line 638, in install_item

    dists = self.install_eggs(spec, download, tmpdir)

  File "/usr/lib/python2.7/dist-packages/setuptools/command/easy_install.py", line 828, in install_eggs

    return self.build_and_install(setup_script, setup_base)

  File "/usr/lib/python2.7/dist-packages/setuptools/command/easy_install.py", line 1105, in build_and_install

    self.run_setup(setup_script, setup_base, args)

  File "/usr/lib/python2.7/dist-packages/setuptools/command/easy_install.py", line 1096, in run_setup

    raise DistutilsError("Setup script exited with %s" % (v.args[0],))

distutils.errors.DistutilsError: Setup script exited with error: command 'gcc' failed with exit status 1

Не могли бы вы помочь мне в решении этой ошибки.