Crypto RSA Signing and Verification in Golang

 

RSA [Rivest-shamir-Adleman] encryption is one of the most widely used algorithms for secure data encryption.

Signing and Verification: 

RSA works by generating form of key pair of private and public keys.

For Signing: 

we need to provide some inputs, 

1. A random reader used for generating random bits because if we provide the same input, it doesn't give the same output as last time.
2. Before signing, we need to hash our message.
3. we also need to provide which hash function is used for message hashing.
4. Finally, private key. 

For Verifying:

we need to provide some inputs, 

1. hash of our message.
2. which hash function is used for message hashing while signing.
3. Finally, public key and signature what we obtained while signing. 

Example:

 package main
 import (
	"crypto"
	"crypto/rand"
	"crypto/rsa"
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"log"
 )
 func main() {
	privatekey, publickey := GenerateRsaKeys()
	message := "hello"
	hashedMessage := sha256.Sum256([]byte(message))
	signedBytes, err := rsa.SignPKCS1v15(rand.Reader, privatekey, crypto.SHA256, hashedMessage[:])
	if err != nil {
		fmt.Println("signing error using RSA keys")
		log.Fatal(err)
	}
	err = rsa.VerifyPKCS1v15(publickey, crypto.SHA256, hashedMessage[:], signedBytes)
	if err != nil {
		fmt.Println("signing error using RSA keys")
		log.Fatal(err)
	}
	fmt.Println("Message verified Successfully")
}

func GenerateRsaKeys() (*rsa.PrivateKey, *rsa.PublicKey) {
	privatekey, err := rsa.GenerateKey(rand.Reader, 4096)
	if err != nil {
		fmt.Println("cannot generate RSA keys")
		log.Fatal(err)
	}
	publicKey := &privatekey.PublicKey
	return privatekey, publicKey
}

Output:

Message verified Successfully