找不到RSAEncryptionPadding

Question

我一直在尝试在C＃中更改加密函数的填充和散列模式：

https://msdn.microsoft.com/en-us/library/mt132684(v=vs.110).aspx

我试过了：

using System.Security.Cryptography;
...
RSACryptoServiceProvider rsaAlg = new RSACryptoServiceProvider ();
byte[] encrypted = rsaAlg.Encrypt (
                      System.Text.ASCIIEncoding.Default.GetBytes (msg),
                      RSAEncryptionPadding.OaepSHA1);    

编译期间发生错误：无法找到类型或命名空间名称RSAEncryptionPadding。

如何更改填充？