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diff --git a/sites/www/installing.rst b/sites/www/installing.rst index 3e96a50f..f16369ff 100644 --- a/sites/www/installing.rst +++ b/sites/www/installing.rst @@ -66,6 +66,32 @@ Tools on the Mac, or the ``build-essential`` package on Ubuntu or Debian Linux -- basically, anything with ``gcc``, ``make`` and so forth) as well as the Python development libraries, often named ``python-dev`` or similar. +Slow vs fast crypto math +~~~~~~~~~~~~~~~~~~~~~~~~ + +PyCrypto attempts to use the ``gmp`` C math library if it is present on your +system, which enables what it internally calls "fastmath" (``_fastmath.so``). +When those headers are not available, it falls back to "slowmath" +(``_slowmath.py``) which is a pure-Python implementation. + +Real-world tests have shown significant benefits to using the C version of this +code; thus we strongly recommend you install the ``gmp`` development headers +**before** installing Paramiko/PyCrypto. E.g.:: + + $ apt-get install libgmp-dev # or just apt + $ yum install gmp-devel # or dnf + $ brew install gmp + +If you're unsure which version of math you've ended up with, a quick way to +check is to examine whether ``_fastmath.so`` or ``_slowmath.py`` appears in the +output of:: + + from Crypto.PublicKey import RSA + print(RSA._impl._math) + +Windows +~~~~~~~ + For **Windows** users we recommend using :ref:`pypm`, installing a C development environment such as `Cygwin <http://cygwin.com>`_ or obtaining a precompiled Win32 PyCrypto package from `voidspace's Python modules page |