replace "-prverify privatekey.txt" with "-verify publickey.txt" in signature examples

If you need to extract the public key from the private key you can do so with the following:

openssl rsa -in private.pem -pubout > publickey.txt
replace "inkey privatekey.txt" with "-inkey pubkey.txt -pubin" for OAEP encryption example
redo PKCS1 encryption examples

- replace '1234567890' with file_get_contents('plaintext.txt')
- replace "-inkey privatekey.txt" for encryption with "-inkey publickey.txt -pubin"
- replace "-encrypt" with "-decrypt" for decryption