Reading a certificate signing request with C#

Question

I want to read the contents of a CSR in C#. However, I haven't found any way to do it in C#. What I've found was the namespace System.Security.Cryptography.X509Certificates, but it only handles existing certificates, not certificate requests.

Can anyone give me an hint about it? Thanks in advance.

Answer 1

There is a way, the CertEnroll library which comes with Windows (although I can't say how far back it's been there) allows you to load certificate requests and have them parsed.

First you need to import a reference to the CERTENROLLLib COM library into your project. This will create a CERTENROLLLib name space you can then use.

Then you do something like this;

string csr = "-----BEGIN CERTIFICATE REQUEST-----\r\n" +
             "MIIBnTCCAQYCAQAwXTELMAkGA1UEBhMCU0cxETAPBgNVBAoTCE0yQ3J5cHRvMRIw\r\n" +
             "EAYDVQQDEwlsb2NhbGhvc3QxJzAlBgkqhkiG9w0BCQEWGGFkbWluQHNlcnZlci5l\r\n" +
             "eGFtcGxlLmRvbTCBnzANBgkqhkiG9w0BAQEFAAOBjQAwgYkCgYEAr1nYY1Qrll1r\r\n" +
             "uB/FqlCRrr5nvupdIN+3wF7q915tvEQoc74bnu6b8IbbGRMhzdzmvQ4SzFfVEAuM\r\n" +
             "MuTHeybPq5th7YDrTNizKKxOBnqE2KYuX9X22A1Kh49soJJFg6kPb9MUgiZBiMlv\r\n" +
             "tb7K3CHfgw5WagWnLl8Lb+ccvKZZl+8CAwEAAaAAMA0GCSqGSIb3DQEBBAUAA4GB\r\n" +
             "AHpoRp5YS55CZpy+wdigQEwjL/wSluvo+WjtpvP0YoBMJu4VMKeZi405R7o8oEwi\r\n" +
             "PdlrrliKNknFmHKIaCKTLRcU59ScA6ADEIWUzqmUzP5Cs6jrSRo3NKfg1bd09D1K\r\n" +
             "9rsQkRc9Urv9mRBIsredGnYECNeRaK5R1yzpOowninXC\r" + 
             "-----END CERTIFICATE REQUEST-----";

CX509CertificateRequestPkcs10 request = new CX509CertificateRequestPkcs10();
request.InitializeDecode(csr, EncodingType.XCN_CRYPT_STRING_BASE64_ANY);
request.CheckSignature();

Console.WriteLine(((CX500DistinguishedName)request.Subject).Name);
Console.WriteLine(request.PublicKey.Length);
Console.WriteLine(request.HashAlgorithm.FriendlyName);

You can see the only fun part is getting the subject name out, as you need to cast it to a CX500DistinguishedName instance first.

Answer 2

Look at BouncyCastle's C# implementation. Used it for PGP stuff in the past, worked great. Something like this should get you started (not tested):

var textReader = File.OpenText(...);
var reader = new Org.BouncyCastle.OpenSsl.PEMReader(textReader);
var req = reader.ReadObject() as Org.BouncyCastle.Pkcs.Pkcs10CertificationRequest;
var info = req.GetCertificationRequestInfo();
Console.WriteLine(info.Subject);