This is forked from https://github.com/rkraevskiy/ubootpubkey.git to write the public key(s) directly to a binary device tree
instead of being added to the device tree source.
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Keys generation

Generate a private key:

openssl genrsa -out keys/uboot_sign_key.key 4096

Generate public key from private key:

openssl rsa -in keys/uboot_sign_key.key -pubout -out keys/uboot_sign_key.pem

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After compiling u-boot, add the signature node with the public key to the uboot control
device tree u-boot.dtb

ubpubkey.py --pubkey keys/uboot_sign_key.pem --keynode key-my_key --outfile u-boot.dtb

Several keys can be added like this:

ubpubkey.py --pubkey keys/uboot_sign_key.pem keys2/uboot_sign_key.pem --keynode key-my_key key-my_key2 --outfile u-boot.dtb --set-any-key