Golang golang-aesgcm (snippet)

Go programming example 'golang-aesgcm'

golang-aesgcm

Golang beginners example: golang-aesgcm

package main

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

// AesGcmEncrypt takes an encryption key and a plaintext string and encrypts it with AES256 in GCM mode, which provides authenticated encryption. Returns the ciphertext and the used nonce.
func AesGcmEncrypt(key []byte, plaintext string) (ciphertext, nonce []byte) {
    plaintextBytes := []byte(plaintext)

    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, plaintextBytes, nil)
    fmt.Printf("Ciphertext: %x\n", ciphertext)
    fmt.Printf("Nonce: %x\n", nonce)

    return
}

// AesGcmDecrypt takes an decryption key, a ciphertext and the corresponding nonce and decrypts it with AES256 in GCM mode. Returns the plaintext string.
func AesGcmDecrypt(key, ciphertext, nonce []byte) (plaintext string) {
    block, err := aes.NewCipher(key)
    if err != nil {
        panic(err.Error())
    }

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

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

    plaintext = string(plaintextBytes)
    fmt.Printf("%s\n", plaintext)

    return
}

func main() {
    // Generate an encryption key. 16 bytes = AES-128, 32 bytes = AES-256.
    key := make([]byte, 32)
    if _, err := io.ReadFull(rand.Reader, key); err != nil {
        panic(err.Error())
    }

    // Specify the plaintext input
    plaintext := "Lorem Ipsum"
    ciphertext, nonce := AesGcmEncrypt(key, plaintext)

    // For decryption you need to provide the nonce which was used for the encryption
    plaintext = AesGcmDecrypt(key, ciphertext, nonce)
}

Useful links

• Learn Go: https://golangr.com
• Download Go: https://golang.org