golang aes-256-gcm no-magic

aes-256-gcm.go

package main

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"fmt"
	"io"
)

func ExampleNewGCMEncrypter(input string) ([]byte, []byte) {
	// The key argument should be the AES key, either 16 or 32 bytes
	// to select AES-128 or AES-256.
	key := []byte("AES256Key-32Characters1234567890")
	plaintext := []byte(input)

	block, err := aes.NewCipher(key)
	if err != nil {
		panic(err.Error())
	}

	// Never use more than 2^32 random nonces with a given key because of the risk of a repeat.
	nonce := make([]byte, 12)
	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
		panic(err.Error())
	}
    fmt.Printf("Nonce:%x\n", nonce)

	aesgcm, err := cipher.NewGCM(block)
	if err != nil {
		panic(err.Error())
	}

	ciphertext := aesgcm.Seal(nil, nonce, plaintext, nil)
	fmt.Printf("Cyphertext:%x\n", ciphertext)
	
	return ciphertext, nonce
}

func ExampleNewGCMDecrypter(ciphertext []byte, nonce[]byte) {
	// The key argument should be the AES key, either 16 or 32 bytes
	// to select AES-128 or AES-256.
	key := []byte("AES256Key-32Characters1234567890")
	
	block, err := aes.NewCipher(key)
	if err != nil {
		panic(err.Error())
	}

	aesgcm, err := cipher.NewGCM(block)
	if err != nil {
		panic(err.Error())
	}

	plaintext, err := aesgcm.Open(nil, nonce, ciphertext, nil)
	if err != nil {
		panic(err.Error())
	}

	fmt.Printf("Plaintext: %s\n", plaintext)
	// Output: exampleplaintext
}

func main() {
    cyphertext, nonce := ExampleNewGCMEncrypter("exampleplaintext")
    ExampleNewGCMDecrypter(cyphertext, nonce)
}