TL;DR how to I extract the raw form of the public key so I can do sha256 around it?
My chip’s ROM is super limited and I simply cannot afford to have certificate support compiled. Because, of the limitation, I only have
SHA256 compiled in, that’s all.
So I am trying to make a very simplified setup:
CAalternative, a public key to a master key.
device.pem- A device’s RSA key pair
device.sig- A “signature” of the device.pub, by basically doing
rsa.sign(ca.pem, sha256(device.pub))once and uploading it to the device
So devices can verify each other by
rsa.verify(ca.pub, sha256(otherdevice.pub), otherdevice.sig)
The question would be, how to I extract the raw form of the public key so I can do sha256 around it? Something like openssl’s
openssl rsa -in device.pub -pubin -outform der | openssl dgst -sha256
P.S. An offtopic question, is there a way to turn
base64 off and do keys if “binary” so I can save ROM?