How to sign data using asymmetric key cryptography in Go?

To sign data using asymmetric key cryptography in Go, you can use the crypto and crypto/rand packages. Here's an example code to demonstrate the process:

package main

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

func main() {
	// Generate RSA key pair
	privateKey, err := rsa.GenerateKey(rand.Reader, 2048)
	if err != nil {
		fmt.Println("Error generating private key:", err)
		return
	}

	// Create a digest of the data to be signed
	data := []byte("Hello, World!")
	hash := sha256.Sum256(data)

	// Sign the digest using the private key
	signature, err := rsa.SignPKCS1v15(rand.Reader, privateKey, crypto.SHA256, hash[:])
	if err != nil {
		fmt.Println("Error signing data:", err)
		return
	}

	fmt.Println("Data:", string(data))
	fmt.Printf("Signature: %x\n", signature)

	// Verify the signature using the public key (can be done by anyone)
	publicKey := privateKey.PublicKey
	err = rsa.VerifyPKCS1v15(&publicKey, crypto.SHA256, hash[:], signature)
	if err != nil {
		fmt.Println("Signature verification failed:", err)
		return
	}

	fmt.Println("Signature verified successfully.")
}

Here's a brief explanation of the code:

Generate an RSA private key using rsa.GenerateKey from the crypto/rsa package.
Create a digest of the data you want to sign. In this example, we use the SHA-256 hash function from the crypto/sha256 package.
Sign the digest using rsa.SignPKCS1v15 with the private key.
Print the data and the signature.
Verify the signature using rsa.VerifyPKCS1v15 with the corresponding public key. Note that the public key can be shared and used by anyone for verification.

Make sure to import the required packages at the beginning of your code:

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

This example shows how to sign and verify data using RSA. You can also use other asymmetric key algorithms like ECDSA by replacing rsa with ecdsa where applicable.