I have an application which is making use of the RSACryptoServiceProvider to decrypt some data using a known private key (stored in a variable). 

When the IIS Application Pool is configured to use Network Service, everything runs fine. 

However, when we configure the IIS Application Pool to run the code under a different Identity, we get the following: 

```
System.Security.Cryptography.CryptographicException: The system cannot find the file specified.

   at System.Security.Cryptography.Utils.CreateProvHandle(CspParameters parameters, Boolean randomKeyContainer)
   at System.Security.Cryptography.RSACryptoServiceProvider.ImportParameters(RSAParameters parameters)
   at System.Security.Cryptography.RSA.FromXmlString(String xmlString)

```

The code is something like this: 

```
byte[] input; 
byte[] output; 
string private_key_xml; 

var provider = new System.Cryptography.RSACryptoServiceProvider(this.m_key.Key_Size);
provider.FromXmlString(private_key_xml); // Fails Here when Application Pool Identity != Network Service

ouput = provider.Decrypt(input, false); // False = Use PKCS#1 v1.5 Padding

```

There are resources which attempt to answer it by stating that you should give the user read access to the machine key store - however there is no definitive answer to solve this issue. 

Environment: IIS 6.0, Windows Server 2003 R2, .NET 3.5 SP1