AES GCM Example

aes-gcm-decrypt.go

// Copyright 2021 Abhijit Bose. All rights reserved.
// Use of this source code is governed by a Apache 2.0 license

package main

import (
	"crypto/aes"
	"crypto/cipher"
	"encoding/hex"
	"fmt"
)

func main() {
	// Load your secret key from a safe place and reuse it across multiple
	// Seal/Open calls. (Obviously don't use this example key for anything
	// real.) If you want to convert a passphrase to a key, use a suitable
	// package like bcrypt or scrypt.
	// When decoded the key should be 16 bytes (AES-128) or 32 (AES-256).
	key, _ := hex.DecodeString("6368616e676520746869732070617373776f726420746f206120736563726574")
	ciphertext, _ := hex.DecodeString("022100c774487456c404b3bb9b3938c7234b3837746a27fbd84a91df5d3ba62e")
	nonce, _ := hex.DecodeString("eed01d5099dc428d44bb18f1")

	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", plaintext)
}

aes-gcm-encrypt.go

// Copyright 2021 Abhijit Bose. All rights reserved.
// Use of this source code is governed by a Apache 2.0 license

package main

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

func main() {
	// Load your secret key from a safe place and reuse it across multiple
	// Seal/Open calls. (Obviously don't use this example key for anything
	// real.) If you want to convert a passphrase to a key, use a suitable
	// package like bcrypt or scrypt.
	// When decoded the key should be 16 bytes (AES-128) or 32 (AES-256).
	key, _ := hex.DecodeString("6368616e676520746869732070617373776f726420746f206120736563726574")
	plaintext := []byte("exampleplaintext")

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

	aesgcm, err := cipher.NewGCM(block)
	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, aesgcm.NonceSize())
	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
		panic(err.Error())
	}
	fmt.Printf("nonce : %x\n", nonce)

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