在WP8上解密AES 128位RijndaelManaged

这段代码有点问题。

var symmetricKey = new RijndaelManaged { Mode = CipherMode.CBC, IV = iv, KeySize = 128, Key = keyBytes, Padding = PaddingMode.Zeros };
using (var decryptor = symmetricKey.CreateDecryptor())
using (var ms = new MemoryStream(cipherTextBytes))
using (var cs = new CryptoStream(ms, decryptor, CryptoStreamMode.Read))
{
    var plainTextBytes = new byte[cipherTextBytes.Length];
    int decryptedByteCount = cs.Read(plainTextBytes, 0, plainTextBytes.Length);
    return Encoding.UTF8.GetString(plainTextBytes, 0, decryptedByteCount);
}

问题在这里:

var symmetricKey = new RijndaelManaged { Mode = CipherMode.CBC, IV = iv,
                                         KeySize = 128, Key = keyBytes,
                                         Padding = PaddingMode.Zeros };

因为即使我包含了System.Security.Cryptography，它也找不到RijndaelManaed。上面写着:

"命名空间未找到。可能使用汇编引用"

"

事实上，当我添加using System.Security.Cryptography时，只有选项可用:

• Pkcs
• x509certificate
Xml>

我需要使用System.Security.Cryptography.RijndaelManaged