signverify.go

package main

import (
	"crypto"
	"crypto/rand"
	"crypto/rsa"
	"crypto/sha256"
	"fmt"
)

func Example() {
	// The GenerateKey method takes in a reader that returns random bits, and
	// the number of bits
	privateKey, err := rsa.GenerateKey(rand.Reader, 2048)
	if err != nil {
		panic(err)
	}

	// The public key is a part of the *rsa.PrivateKey struct
	publicKey := privateKey.PublicKey

	msg := []byte("verifiable message")

	// Before signing, we need to hash our message
	// The hash is what we actually sign
	msgHash := sha256.New()
	_, err = msgHash.Write(msg)
	if err != nil {
		panic(err)
	}
	msgHashSum := msgHash.Sum(nil)

	// In order to generate the signature, we provide a random number generator,
	// our private key, the hashing algorithm that we used, and the hash sum
	// of our message
	// signature, err := rsa.SignPSS(rand.Reader, privateKey, crypto.SHA256, msgHashSum, nil)
	signature, err := rsa.SignPKCS1v15(rand.Reader, privateKey, crypto.SHA256, msgHashSum)
	if err != nil {
		panic(err)
	}

	// To verify the signature, we provide the public key, the hashing algorithm
	// the hash sum of our message and the signature we generated previously
	// there is an optional "options" parameter which can omit for now
	err = rsa.VerifyPKCS1v15(&publicKey, crypto.SHA256, msgHashSum, signature)
	if err != nil {
		fmt.Println("could not verify signature: ", err)
		return
	}
	// If we don't get any error from the `VerifyPSS` method, that means our
	// signature is valid
	fmt.Println("signature verified")
}