C# 字串處理實戰：DES 加解密與 Null、Empty、Nothing 差異解析 (第 4 部分)

1. DES 對稱加密範例

使用 DESCryptoServiceProvider 進行加密，輸出 Base64 字串：

textBox1.ReadOnly = false;
try
{
    DESCryptoServiceProvider des = new DESCryptoServiceProvider();
    byte[] key = Encoding.Unicode.GetBytes(encryptKey); // 金鑰需 8 位元組
    byte[] data = Encoding.Unicode.GetBytes(textBox1.Text.Trim());

    MemoryStream ms = new MemoryStream();
    CryptoStream cs = new CryptoStream(ms, des.CreateEncryptor(key, key), CryptoStreamMode.Write);
    cs.Write(data, 0, data.Length);
    cs.FlushFinalBlock();

    textBox2.Text = Convert.ToBase64String(ms.ToArray());
    textBox3.Text = "";
    textBox3.ReadOnly = true;
}
catch (Exception ex)
{
    MessageBox.Show(ex.Message, "資訊", MessageBoxButtons.OK, MessageBoxIcon.Information);
}

2. DES 解密範例 (搭配上例使用)

textBox3.ReadOnly = false;
try
{
    DESCryptoServiceProvider des = new DESCryptoServiceProvider();
    byte[] key = Encoding.Unicode.GetBytes(encryptKey);
    byte[] data = Convert.FromBase64String(textBox2.Text.Trim());

    MemoryStream ms = new MemoryStream();
    CryptoStream cs = new CryptoStream(ms, des.CreateDecryptor(key, key), CryptoStreamMode.Write);
    cs.Write(data, 0, data.Length);
    cs.FlushFinalBlock();

    textBox3.Text = Encoding.Unicode.GetString(ms.ToArray());
    textBox1.Text = "";
    textBox1.ReadOnly = true;
}
catch (Exception ex)
{
    MessageBox.Show(ex.Message, "資訊", MessageBoxButtons.OK, MessageBoxIcon.Information);
}

3. 關鍵字差異總結

補充

常用操作如首字大寫、字串比較、子串插入等較簡單，此處略過。