GoでAESアルゴリズム(CBCモード)を使った実装をする ref: https://qiita.com/ken5scal/items/22efdace02b199f7007f

file0.txt

func EncryptByCBCMode(key []byte, plainText string) ([]byte, error) {
    if len(plainText) % aes.BlockSize != 0 {
        panic("Plain text must be multiple of 128bit")
    }

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

    cipherText := make([]byte,  aes.BlockSize + len(plainText)) // 初期化ベクトルを保存するためにaes.BlockSizeを加えている
    iv := cipherText[:aes.BlockSize] // Unique iv is required
    _, err = rand.Read(iv); if err != nil {
        return nil, err
    }

    cbc := cipher.NewCBCEncrypter(block, iv)
    cbc.CryptBlocks(cipherText[aes.BlockSize:], []byte(plainText))

    return cipherText, nil
}

file1.txt

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

    if len(cipherText) < aes.BlockSize {
        panic("cipher text must be longer than blocksize")
    } else if len(cipherText) % aes.BlockSize != 0 {
        panic("cipher text must be multiple of blocksize(128bit)")
    }
    iv := cipherText[:aes.BlockSize] // assuming iv is stored in the first block of ciphertext
    cipherText = cipherText[aes.BlockSize:]
    plainText := make([]byte, len(cipherText))

    cbc := cipher.NewCBCDecrypter(block, iv)
    cbc.CryptBlocks(plainText, cipherText)
    fmt.Println(plainText)
    return string(plainText), nil
}

file2.txt

func main() {
    cipherText, _ = EncryptByCBCMode(key, "1234567891234567") // 16bye
    fmt.Println(cipherText)
    cipherText, _ = EncryptByCBCMode(key, "12345678912345671234123412341234") // 32byte
    fmt.Println(cipherText)
        // iv(32 byte) + 16byte

    plainText, _ = DecryptByCBCMode(key, cipherText)
    fmt.Println(plainText)
        // 12345678912345671234123412341234
}