Encrypt and decrypt a plaintext with AES-GCM in Go. Plaintext is passed in as command line argument.

aesgcm.go

package main

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

func main() {
    if len(os.Args) < 2 {
        fmt.Println("Usage: aesgcm <plaintext>")
        os.Exit(0)
    }

    fmt.Println("Plaintext = " + os.Args[1])

    // Get plaintext as a byte slice
    plaintext := []byte(os.Args[1])

    // Randomly generate a 32 byte (128 bit) AES key
    key := make([]byte, 32)
    if _, err := io.ReadFull(rand.Reader, key); err != nil {
        panic(err.Error())
    }

    fmt.Printf("Key = %x\n", key)

    // Get an AES cipher instance using the key
    block, err := aes.NewCipher(key)
    if err != nil {
        panic(err.Error())
    }

    // Generate a nonce for GCM
    nonce := make([]byte, 12)
    if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
        panic(err.Error())
    }

    // Get GCM instance that uses the AES cipher
    aesgcm, err := cipher.NewGCM(block)
    if err != nil {
        panic(err.Error())
    }

    // Perform AES-GCM encryption with generated nonce
    ciphertext := aesgcm.Seal(nil, nonce, plaintext, nil)
    fmt.Printf("Ciphertext = %x\n", ciphertext)

    // Now perform decryption of the ciphertext
    plaintextNew, err := aesgcm.Open(nil, nonce, ciphertext, nil)
    if err != nil {
        panic(err.Error())
    }

    fmt.Printf("Decrypted Plaintext = %s\n", plaintextNew)
}