Do not use this tool for new projects! Please use swupdate, Mender or RAUC.
fwupgrade was written many years ago, back when the above solutions didn't exist. fwupgrade is not maintained, poorly written, has no security features and probably lots of other issues. You have been warned.
fwupgrade is published under the terms of the GPLv2 license, which text is available in LICENSE.GPLv2.
fwupgrade includes code from the U-Boot project (md5.c, crc32.c). crc32.c itself comes from the Zlib project, and is released under the Zlib license, which text is available in LICENSE.zlib.