How to get the private key from a separate file?

Question

I have an Apache (xampp/wamp) server that provides a SSL connection on port 443. It uses two certificate files: server.cert and server.key when the latter conains the private key.

I have another server configured to listen to requests on port 843 (flash policy stuff) and response to a certain request with some text reply written in C# which runs separately.

In order to achieve SSL connectivity, i use a flex object called SecureSocket which allowes that, however, it uses the original servers certificate in order to encrypt the request.

My goal is to teach my 843 C# server to decrypt the sent data and encrypt the reply and for this i'm using the X509Certificate object in C#.

However, since the pub and priv keys are on different files, i'm getting FALSE on the following:

string text = System.IO.File.ReadAllText(@"C:\xampp\apache\conf\ssl.crt\server.crt");
UTF8Encoding encoding = new System.Text.UTF8Encoding();
byte[] byteCert = encoding.GetBytes(text);
X509Certificate2 uberCert = new X509Certificate2();
uberCert.Import(byteCert);
Console.WriteLine("Has privateKey:" + uberCert.HasPrivateKey.ToString());
Console.WriteLine("PrivateKey: \n" + uberCert.PrivateKey);

Obviously, the False on uberCert.HasPrivateKey comes from the fact that the private key is on a different file, so my questions are:

1.How can i read the private key using the X509CErtificate2 object? 2.How can i use the public key in order to decrypt the received message and how to re-encrypt it with the private key (in order to send the encrypted response back) ?

Thanks in advance,

Mike.

score 1 · Answer 1 · answered Jul 17 '17 at 20:25

I've created a small helper NuGet package (based on opensslkey) to create a X509 certificate based on public key and private (rsa) key.

// Generate with: openssl req -x509 -sha256 -nodes -days 365 -newkey rsa:2048 -keyout private.key -out certificate_pub.crt
string certificateText = File.ReadAllText("certificate_pub.crt");
string privateKeyText = File.ReadAllText("private.key");

ICertificateProvider provider = new CertificateFromFileProvider(certificateText, privateKeyText);
X509Certificate2 certificate = provider.Certificate;

// Example: use the PrivateKey from the certificate above for signing a JWT token using Jose.Jwt:
string token = Jose.JWT.Encode(payload, certificate.PrivateKey, JwsAlgorithm.RS256);

See NuGet and Github-project for functionality and code-examples.

score 0 · Answer 2 · answered Feb 21 '12 at 13:15

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The private key is likely PEM encoded PKCS#8 structure.

The Mono project provides code to read this format (among other) in the Mono.Security.dll assembly. This assembly is purely managed and will work on Windows, Linux or OSX.

answered Feb 21 '12 at 13:15

poupou

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score 0 · Answer 3 · edited May 23 '17 at 12:06

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You can't in straight .NET.

You can either use BouncyCastle (see this answer: How to read a PEM RSA private key from .NET) or use a PKCS12 container instead for the username + password, which you can create using OpenSSL's tools from the PEM files.

edited May 23 '17 at 12:06

Community

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answered Feb 21 '12 at 13:18

Joe

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Hi @Joe, I've done the following: `X509Certificate2 uberCert = new X509Certificate2(@"C:\xampp\apache\conf\server.pfx","qwe123",X509KeyStorageFlags.MachineKeySet);` after combining both keys into a single pfx file using openssl. It replies with true if i check whether a private key exists, yet i don't know how use it in order to decipher my not Base64 encoded requests. When using the link you've provided, all i'm getting are exceptions. any tips? – silicakes Feb 22 '12 at 10:17

How to get the private key from a separate file?

3 Answers3