From http://www.kerneli.org

Included only if USE=crypto is set.

Due to previous regulations on export and use of
crypto, especially in the US, the Linux source
distribution has not contained crypto up to this
point.  The International Kernel Patch and 
CryptoAPI team have tried to remedy this situation
by providing the missing functionality in the form
of a unified patch to the Linux kernel source.  [A
patch is the difference between two sources - the
International Kernel Patch is distributed as the
difference between the original Linux source
distribution and the "International" Linux source
distribution].  Lately, some US export restrictions
have been lifted, and it is therefore possible that
crypto will be part of the linux kernel source code
in the future. However, until that happens, this is
where you can get crypto support in your linux
kernel.

The International Kernel Patch is not endorsed by
Linus Torvalds and should therefore not be considered
to be part of the official Linux kernel source.

See the Electronic Frontier Foundation for more
information about the issues regarding export of
crypto.

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