libemsha
========

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This library is an MIT-licensed HMAC-SHA-256 C++11 library designed for
embedded systems. It is built following the JPL [Power of
Ten](http://spinroot.com/gerard/pdf/P10.pdf) rules. It was written in
response to a need for a standalone HMAC-SHA-256 package that could run
on several platforms.

Getting and Building the Source
-------------------------------

The source code is available via
[Github](https://github.com/kisom/libemsha/); each version should be git
tagged. :

    git clone https://github.com/kisom/libemsha
    git clone git@github.com:kisom/libemsha

The current release is
[1.0.1](https://github.com/kisom/libemsha/releases/tag/v1.0.1).

The project is built using Autotools and `make`.

When building from a git checkout, the [autobuild]{.title-ref} script
will bootstrap the project from the autotools sources (e.g. via
`autoreconf -i`), run `configure` (by default to use clang), and attempt
to build the library and run the unit tests.

Once the autotools infrastructure has been bootstrapped, the following
should work: :

    ./configure && make && make check && make install

There are three flags to `configure` that might be useful:

-   `--disable-hexstring` disables the provided `hexstring` function;
    while this might be useful in many cases, it also adds extra size to
    the code.
-   `--disable-hexlut` disables the larger lookup table used by
    `hexstring`, which can save around a kilobyte of program space. If
    the `hexstring` function is disabled, this option has no effect.
-   `--disable-selftest` disables the internal self-tests, which can
    reclaim some additional program space.

Documentation
-------------

Documentation is currently done with [Sphinx](http://sphinx-doc.org/).
See `doc/`.

### See also

-   [FIPS 180-4, the Secure Hash
    Standard](http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.180-4.pdf)
-   [FIPS 198-1, The Keyed-Hash Message Authentication Code
    (HMAC)](http://csrc.nist.gov/publications/fips/fips198-1/FIPS-198-1_final.pdf)
-   [RFC 2014, HMAC: Keyed-Hashing for Message
    Authentication](https://tools.ietf.org/html/rfc2104)
-   [RFC 6234, US Secure Hash Algorithms (SHA and SHA-based HMAC and
    HKDF)](https://tools.ietf.org/html/rfc6234)[^1]
-   The behaviour of this package was cross-checked using the Go 1.5.1
    linux/amd64 standard library\'s
    [crypto/sha256](https://golang.org/src/crypto/sha256/) package.

**Footnotes**

[^1]: This library came about after extracting the relevant C code from
    RFC 6234, and needing a C++ version. It draws heavy inspiration from
    that code base.