AES-256 GCM Encryption Example in Golang

aes256-gcm.go

package example_test

import (
	"crypto/aes"
	"crypto/cipher"
	"hex"
	"io"
)

// AES-GCM should be used because the operation is an authenticated encryption
// algorithm designed to provide both data authenticity (integrity) as well as
// confidentiality.

// Merged into Golang in https://go-review.googlesource.com/#/c/18803/

func ExampleNewGCMEncrypter() {
	// 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("exampleplaintext")

	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())
	}

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

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

func ExampleNewGCMDecrypter() {
	// The key argument should be the AES key, either 16 or 32 bytes
	// to select AES-128 or AES-256.
	key := []byte("AES256Key-32Characters1234567890")
	ciphertext, _ := hex.DecodeString("f90fbef747e7212ad7410d0eee2d965de7e890471695cddd2a5bc0ef5da1d04ad8147b62141ad6e4914aee8c512f64fba9037603d41de0d50b718bd665f019cdcd")

	nonce, _ := hex.DecodeString("bb8ef84243d2ee95a41c6c57")

	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("%s\n", string(plaintext))
}

@lukejoshuapark thanks for the feedback, this was not and is not a "use this example for whatever encryption you want". For the original use case, the code has been vetted by an outside security firm and the points you raised are not in play for the use case this specific code was designed for.