AES Encryption Example in Golang

aes_encryption.go

// Playbook - http://play.golang.org/p/3wFl4lacjX

package main

import (
    "bytes"
    "crypto/aes"
    "crypto/cipher"
    "crypto/rand"
    "encoding/base64"
    "errors"
    "fmt"
    "io"
    "strings"
)

func addBase64Padding(value string) string {
    m := len(value) % 4
    if m != 0 {
        value += strings.Repeat("=", 4-m)
    }

    return value
}

func removeBase64Padding(value string) string {
    return strings.Replace(value, "=", "", -1)
}

func Pad(src []byte) []byte {
    padding := aes.BlockSize - len(src)%aes.BlockSize
    padtext := bytes.Repeat([]byte{byte(padding)}, padding)
    return append(src, padtext...)
}

func Unpad(src []byte) ([]byte, error) {
    length := len(src)
    unpadding := int(src[length-1])

    if unpadding > length {
        return nil, errors.New("unpad error. This could happen when incorrect encryption key is used")
    }

    return src[:(length - unpadding)], nil
}

func encrypt(key []byte, text string) (string, error) {
    block, err := aes.NewCipher(key)
    if err != nil {
        return "", err
    }

    msg := Pad([]byte(text))
    ciphertext := make([]byte, aes.BlockSize+len(msg))
    iv := ciphertext[:aes.BlockSize]
    if _, err := io.ReadFull(rand.Reader, iv); err != nil {
        return "", err
    }

    cfb := cipher.NewCFBEncrypter(block, iv)
    cfb.XORKeyStream(ciphertext[aes.BlockSize:], []byte(msg))
    finalMsg := removeBase64Padding(base64.URLEncoding.EncodeToString(ciphertext))
    return finalMsg, nil
}

func decrypt(key []byte, text string) (string, error) {
    block, err := aes.NewCipher(key)
    if err != nil {
        return "", err
    }

    decodedMsg, err := base64.URLEncoding.DecodeString(addBase64Padding(text))
    if err != nil {
        return "", err
    }

    if (len(decodedMsg) % aes.BlockSize) != 0 {
        return "", errors.New("blocksize must be multipe of decoded message length")
    }

    iv := decodedMsg[:aes.BlockSize]
    msg := decodedMsg[aes.BlockSize:]

    cfb := cipher.NewCFBDecrypter(block, iv)
    cfb.XORKeyStream(msg, msg)

    unpadMsg, err := Unpad(msg)
    if err != nil {
        return "", err
    }

    return string(unpadMsg), nil
}

func main() {
    key := []byte("LKHlhb899Y09olUi")
    encryptMsg, _ := encrypt(key, "Hello World")
    msg, _ := decrypt(key, encryptMsg)
    fmt.Println(msg) // Hello World
}