This is part of my post "Just enough cryptography for better securing your apps"

main.go

package main

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/hmac"
	"crypto/rand"
	"crypto/sha1"
	"crypto/sha256"
	"encoding/base64"
	"fmt"
	"io"

	"golang.org/x/crypto/pbkdf2"
)

func decryptAESGCM(key []byte, data []byte) string {
	block, err := aes.NewCipher(key)
	if err != nil {
		return err.Error()
	}
	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return err.Error()
	}
	nonceSize := gcm.NonceSize()
	nonce, cipherText := data[:nonceSize], data[nonceSize:]
	plaintext, err := gcm.Open(nil, nonce, cipherText, nil)
	if err != nil {
		return err.Error()
	}
	return string(plaintext)
}

func encryptAESGCM(key []byte, message []byte) string {
	block, _ := aes.NewCipher(key)
	nonce := make([]byte, 12)
	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
		panic(err.Error())
	}
	aesgcm, err := cipher.NewGCM(block)
	if err != nil {
		panic(err.Error())
	}
	ciphertext := aesgcm.Seal(nonce, nonce, message, nil)
	return base64.StdEncoding.EncodeToString(ciphertext)
}

func deriveKey(key []byte, salt []byte) string {
	derivedKey := pbkdf2.Key(key, salt, 4096, 32, sha1.New)
	return base64.StdEncoding.EncodeToString(derivedKey)
}

func computeHmac256(message []byte, key []byte) string {
	h := hmac.New(sha256.New, key)
	h.Write(message)
	return base64.StdEncoding.EncodeToString(h.Sum(nil))
}

func main() {
	message := []byte("hello world")
	key := []byte("super secret key")
	messageHmac := computeHmac256(message, []byte("cryptographic key"))
	fmt.Println(string(message), messageHmac)
	fmt.Println(string(key), deriveKey(key, []byte("E1F53135E559C253")))
	cipherText := encryptAESGCM(key, message)
	fmt.Println(string(message), cipherText)
	data, _ := base64.StdEncoding.DecodeString(cipherText)
	fmt.Println(cipherText, decryptAESGCM(key, data))
}