Good resources https://linuxconfig.org/using-openssl-to-encrypt-messages-and-files-on-linux Public key encrypt / private key decrypt – RSA (small files) Note RSA (rsault) is only suitable for very small files and is typically used to encrypt a randomly chosen private key that a larger file gets encrypted with.  The reason it won't allow use with large files (say over around 512 bytes) […]

SHA256 is widely regarded as a good security hash that's still secure (some others such as MD5 etc are no longer considered secure).  The following process lets you sign and verify files using sha256 Raspbian comes with openssl already and the commands used below are console commands  If you want to execute them programmatically you can use the approach […]