Comments on: Summarizing PKI Certificate Validation

By: Walter Goulet

Walter Goulet — Thu, 12 Jan 2012 13:56:05 +0000

Hi Deepak,

BER (Basic Encoding Rules – en.wikipedia.org/wiki/Basic_Encoding_Rules) is basically just a method to encode certificate data in a protocol message. Sounds like what you are seeing is that your endpoint is not properly configured with a certificate so it’s not sending anything to the peer.

Walter

By: Deepak Khandelwal

Deepak Khandelwal — Tue, 03 Jan 2012 15:36:15 +0000

I am trying to establishing a IPSec tunnel with the authentication method using certificates. the peer end asks for a certificate as certification request payload in the ISAKMP . But my end replied with some BER Error: Empty choice was found.
Any idea what is BER and what can be the problem ??

By: Walter Goulet

Walter Goulet — Wed, 07 Sep 2011 18:53:25 +0000

Thanks! In light of the Diginotar breach, I have some additional thoughts I plan on blogging about soon. You might be interested in this article I wrote up for the InfoSec Institute last month as well: http://resources.infosecinstitute.com/understanding-pki/

By: Jon H

Jon H — Wed, 07 Sep 2011 18:23:29 +0000

Excellent summary – all the pertinent info in one place!

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By: Joe Juric

Joe Juric — Mon, 04 Apr 2011 13:47:39 +0000

I’ve managed to find API which have a mathod that inspect digital signature versus its signer, both for Java and C# (http://www.bouncycastle.org/)

The problem with the Microsoft Verify() method is that its only suitable for basic chain verification, not digital signature (chain verification can be faked through manual certificate creation).
Note that you can’t see method implementation, so you can’t know what degree of basic is implemented.
If you want, you can implement your own chain verification overriding Validate method in your own class MyX509CertificateValidator : X509CertificateValidator.

I’ve also done verification in OpenSSL, and it worked.

Regards, Joe

By: Walter Goulet

Walter Goulet — Mon, 04 Apr 2011 02:34:33 +0000

@joe

I’m not much of a programmer myself; when I do need to inspect and validate certificates I usually use openssl in scripts. I do know that certificate validation is usually a built in function in certificate handling APIs. For example, in the X509Certificate2 class you describe, the verify method (http://msdn.microsoft.com/en-us/library/system.security.cryptography.x509certificates.x509certificate2.verify.aspx) is intended to do just that.

The signatureValue field is well defined in RFC3280, so any API should be able to export that value for you. It’s just a matter of finding an API that exposes the details you need. If it’s an academic exercise and you just want to extract signatures directly, you could try the following openssl command line:
openssl x509 -in cacert.pem -text -certopt ca_default,no_header,no_version,no_serial,no_validity,no_subject,no_issuer,no_signame,no_pubkey,no_extensions -noout

Hope this helps,
Walter

By: Joe Juric

Joe Juric — Sat, 02 Apr 2011 14:36:51 +0000

Hi
First, thank you for your answer.
But, I still have a problem how to validate a certificate (programmatically).
In section eight, you described in detail how one will do so. I got that, but the thing is that I don’t know how to get signatureValue from the certificate
(nor by inspecting certificate “visually” nor by programmatically digging properties,
such as Subject, Issuer, Dates, Thumbprint etc., I’m using C# .NET X509Certificate2 and other related libraries), so I can decrypt the digital signature (with public key of the issuer), and compare its content to a hash that I’ve previously computed., ie validate certificate.

Thank you in advance,
Joe