c# - How to set read permission on the private key file of X.509 certificate from .NET

Question

Here is the code to add a pfx to the Cert store.

X509Store store = new X509Store( StoreName.My, StoreLocation.LocalMachine );
store.Open( OpenFlags.ReadWrite );
X509Certificate2 cert = new X509Certificate2( "test.pfx", "password" );
store.Add( cert );
store.Close();

However, I couldn't find a way to set permission for NetworkService to access the private key.

Can anyone shed some light? Thanks in advance.

Answer 1

This answer is late but I wanted to post it for anybody else that comes searching in here:

I found an MSDN blog article that gave a solution using CryptoKeySecurity here, and here is an example of a solution in C#:

var rsa = certificate.PrivateKey as RSACryptoServiceProvider;
if (rsa != null)
{
    // Modifying the CryptoKeySecurity of a new CspParameters and then instantiating
    // a new RSACryptoServiceProvider seems to be the trick to persist the access rule.
    // cf. http://blogs.msdn.com/b/cagatay/archive/2009/02/08/removing-acls-from-csp-key-containers.aspx
    var cspParams = new CspParameters(rsa.CspKeyContainerInfo.ProviderType, rsa.CspKeyContainerInfo.ProviderName, rsa.CspKeyContainerInfo.KeyContainerName)
    {
        Flags = CspProviderFlags.UseExistingKey | CspProviderFlags.UseMachineKeyStore,
        CryptoKeySecurity = rsa.CspKeyContainerInfo.CryptoKeySecurity
    };

    cspParams.CryptoKeySecurity.AddAccessRule(new CryptoKeyAccessRule(sid, CryptoKeyRights.GenericRead, AccessControlType.Allow));

    using (var rsa2 = new RSACryptoServiceProvider(cspParams))
    {
        // Only created to persist the rule change in the CryptoKeySecurity
    }
}

I'm using a SecurityIdentifier to identify the account but an NTAccount would work just as well.