LZMA SDK is written and placed in the public domain by Igor Pavlov.

Some code in LZMA SDK is based on public domain code from another developers:
  1) PPMd var.H (2001): Dmitry Shkarin
  2) SHA-256: Wei Dai (Crypto++ library)

Anyone is free to copy, modify, publish, use, compile, sell, or distribute the
original LZMA SDK code, either in source code form or as a compiled binary, for
any purpose, commercial or non-commercial, and by any means.

LZMA SDK code is compatible with open source licenses, for example, you can
include it to GNU GPL or GNU LGPL code.