Because of branch, and https server configuration issues, the plain 'go
get' instructions to build imgtool don't work. Add a note to the README
file for imgtool and give some instructions on how to manually clone the
necessary git repositories.
The --key-type (-t) parameter to keygen allows (requires) the user to
specify the type of key to generate. This now supports "ecdsa-p224" and
"ecdsa-256". Note that the curve must match the one coded into the
bootloader.
The imgtool is a simple image signing tool based on the libraries in the
`newt` tool, but appropriate for images that live outside of a Mynewt
project.
This initial version is able to generate, extract public keys from, and
sign ECDSA P-256 keys. The signing tool is also able to add an image
trailer to mark this image for upgrade.
David Brown