```
MD5 md5 = MD5.Create();
byte[] Ostring = System.Text.Encoding.UTF8.GetBytes("original string");
byte[] hashMD5 = md5.ComputeHAsh(Ostring);
StringBuilder sb = new StringBuilder();
for (int i=0; i<hashMD5.Length; i++)
{
   sb.Append(hashMD5[i].ToString("X2"));
}
string strMD5 = sb.ToString();

```

the value of strMD5 I want encrypt it, using the algorithm RSA with a key in DER format "file: aa.key"

How I can do it in c #?