openssl/RSA - Using a Public key to decrypt

Question

I\'m looking to secure the software update procedure for a little device I\'m maintaining that runs Linux. I want to generate an md5sum of the update package\'s contents and the

Answer 1

Let's assume you have generated a public and private RSA key using openssl genrsa:

$ openssl genrsa -out mykey
Generating RSA private key, 512 bit long modulus
...++++++++++++
..........++++++++++++
e is 65537 (0x10001)
$ openssl rsa -in mykey -pubout -out mykey.pub
writing RSA key

You can sign something with the private key like this:

$ md5sum myfile | openssl rsautl -inkey mykey -sign > checksum.signed

You can verify this data using the public key:

$ openssl rsautl -inkey mykey.pub -pubin -in checksum.signed
df713741d8e92b15977ccd6e019730a5  myfile

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