How to encrypt and decrypt files in Go?

To encrypt and decrypt files in Go, you can use the Golang crypto/aes package. Here's an example of how you can encrypt and decrypt files using AES encryption:

package main

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"errors"
	"io"
	"io/ioutil"
	"os"
)

// EncryptFile encrypts a file with AES encryption algorithm
func EncryptFile(key []byte, inputFile, outputFile string) error {
	// Read the input file
	plaintext, err := ioutil.ReadFile(inputFile)
	if err != nil {
		return err
	}

	// Generate a new AES cipher block from the provided key
	block, err := aes.NewCipher(key)
	if err != nil {
		return err
	}

	// Generate a new random IV (initialization vector)
	iv := make([]byte, aes.BlockSize)
	if _, err := io.ReadFull(rand.Reader, iv); err != nil {
		return err
	}

	// Create a new AES-GCM cipher with the generated key and IV
	aesgcm, err := cipher.NewGCM(block)
	if err != nil {
		return err
	}

	// Encrypt the plaintext using AES-GCM and append the IV to the ciphertext
	ciphertext := aesgcm.Seal(nil, iv, plaintext, nil)
	ciphertext = append(iv, ciphertext...)

	// Write the ciphertext to the output file
	return ioutil.WriteFile(outputFile, ciphertext, 0644)
}

// DecryptFile decrypts a file encrypted with AES encryption algorithm
func DecryptFile(key []byte, inputFile, outputFile string) error {
	// Read the input file
	ciphertext, err := ioutil.ReadFile(inputFile)
	if err != nil {
		return err
	}

	// Generate a new AES cipher block from the provided key
	block, err := aes.NewCipher(key)
	if err != nil {
		return err
	}

	// Check if the ciphertext length is valid
	if len(ciphertext) < aes.BlockSize {
		return errors.New("invalid ciphertext")
	}

	// Extract the IV from the beginning of the ciphertext
	iv := ciphertext[:aes.BlockSize]
	ciphertext = ciphertext[aes.BlockSize:]

	// Create a new AES-GCM cipher with the generated key and IV
	aesgcm, err := cipher.NewGCM(block)
	if err != nil {
		return err
	}

	// Decrypt the ciphertext using AES-GCM
	plaintext, err := aesgcm.Open(nil, iv, ciphertext, nil)
	if err != nil {
		return err
	}

	// Write the decrypted plaintext to the output file
	return ioutil.WriteFile(outputFile, plaintext, 0644)
}

func main() {
	key := []byte("16-byte secret key") // Change this to your own secret key
	inputFile := "input.txt"
	encryptedFile := "encrypted.txt"
	decryptedFile := "decrypted.txt"

	err := EncryptFile(key, inputFile, encryptedFile)
	if err != nil {
		panic(err)
	}
	println("File encrypted successfully.")

	err = DecryptFile(key, encryptedFile, decryptedFile)
	if err != nil {
		panic(err)
	}
	println("File decrypted successfully.")
}

In this example, change the key variable to your own 16-byte secret key. Then, run the program to encrypt and decrypt the input.txt file. The encrypted file will be saved as encrypted.txt, and the decrypted file will be saved as decrypted.txt.