Check RSA Signature (golang)

check-rsa-signature.go

package main

import (
	"crypto"
	"crypto/rand"
	"crypto/rsa"
	"crypto/sha256"
	"crypto/x509"
	"encoding/pem"
	"fmt"
	"io/ioutil"
)

func main() {
	prv, err := readPrivate("NZLSpecimen")
	if err != nil {
		fmt.Println("Error reading private key: %v", err)
		panic(err)
	}

	msg := []byte("This is the message to be signed")

	signature, err := signMessage(msg, prv)
	if err != nil {
		fmt.Println("Error generating signature: %v", err)
		panic(err)
	}

	pub, err := readPublic("NZLSpecimenPublic.pem")
	if err != nil {
		fmt.Println("Error reading public key: %v", err)
		panic(err)
	}

	err = checkSignature(msg, signature, pub)
	if err != nil {
		fmt.Println("Signature does not match: %v", err)
		panic(err)
	}

	fmt.Println("Signature matches")
}

func readPrivate(path string) (*rsa.PrivateKey, error) {
	data, err := ioutil.ReadFile(path)
	if err != nil {
		fmt.Println("Error reading private key: %v", err)
		panic(err)
	}

	block, _ := pem.Decode(data)
	return x509.ParsePKCS1PrivateKey(block.Bytes)
}

func readPublic(path string) (*rsa.PublicKey, error) {
	data, err := ioutil.ReadFile(path)
	if err != nil {
		fmt.Println("Error reading public key: %v", err)
		panic(err)
	}

	block, _ := pem.Decode(data)
	return x509.ParsePKCS1PublicKey(block.Bytes)
}

func signMessage(data []byte, key *rsa.PrivateKey) ([]byte, error) {
	hasher := sha256.New()
	hasher.Write(data)
	hashed := hasher.Sum(nil)
	return rsa.SignPKCS1v15(rand.Reader, key, crypto.SHA256, hashed)
}

func checkSignature(data []byte, signature []byte, key *rsa.PublicKey) error {
	hasher := sha256.New()
	hasher.Write(data)
	hashed := hasher.Sum(nil)
	return rsa.VerifyPKCS1v15(key, crypto.SHA256, hashed, signature)
}