Verifying X509Certificate signature

Discussion in 'ASP .Net Security' started by Peter Ritchie [C# MVP], Jul 31, 2008.

  1. Sorry for the cross-post; the last post didn't use the correct MSDN e-mail...

    Can anyone point me in the right direction for verifying an X509Certificates
    signature? i.e. that it was truly signed by a known/trusted certificate

    Thanks -- Peter
     
    Peter Ritchie [C# MVP], Jul 31, 2008
    #1
    1. Advertisements

  2. Peter Ritchie [C# MVP]

    Joe Kaplan Guest

    What is it that you have that is signed? There may be different ways
    depending on the format of the signed object. If it is a PKCS7 signed data
    blob, then the SignedCms class is the way to go and is pretty easy to use.

    Joe K.
     
    Joe Kaplan, Jul 31, 2008
    #2
    1. Advertisements

  3. Hi Peter,

    As you said that you want some information about verifying X509 certificate
    signature, I'd like to confirm what's the exact verification you want.

    My understanding is that you may have a X509 certificate which assocate
    with a publickey/private key pair( of RSA or DSA encypt provider) and
    you've also used the private key to digital signed some data, and want to
    verify the data, correct?

    If this is the case, generally you will need to do two things here:

    1. Retrieve the public/private key from the certificate (in certificate
    store of windows)

    2. use the key info associated with the certificate to do encryption or
    digital sign.

    Here are some web articles introducing some code on this:

    http://www.codeproject.com/KB/security/RSACryptoPad.aspx

    http://www.eggheadcafe.com/articles/20020630.asp

    and here is a simple test function I've written which include accessing
    cert store to retrieve key info in cert and do some RSA signing and
    verification:


    ======================================
    private void btnTest_Click(object sender, EventArgs e)
    {
    RSACryptoServiceProvider rsa;
    RSAParameters key;
    SHA1CryptoServiceProvider sha = new SHA1CryptoServiceProvider();

    bool result;


    signSrc = Encoding.UTF8.GetBytes("ABCDEFG");

    string tp = "2b6f8ac51a85cbaf429474a55304313968667611";
    X509Store store = new X509Store(StoreName.My,
    StoreLocation.CurrentUser);
    store.Open(OpenFlags.ReadOnly);

    X509Certificate2 cert2 =
    store.Certificates.Find(X509FindType.FindByThumbprint, tp, true)[0];

    store.Close();

    rsa = cert2.PrivateKey as RSACryptoServiceProvider;



    signDes = rsa.SignData(signSrc, sha);

    result = rsa.VerifyData(signSrc, sha, signDes);


    MessageBox.Show("valid: " + result);



    /** here try exporting the CERT to a exportable file */


    byte[] pfx_bytes =
    cert2.Export(X509ContentType.Pfx,"Password01!");


    //txtContent.Text = Convert.ToBase64String(pfx_bytes);


    X509Certificate2 filecert = new X509Certificate2();
    filecert.Import(pfx_bytes, "Password01!",
    X509KeyStorageFlags.DefaultKeySet);



    RSACryptoServiceProvider rsa1 = filecert.PrivateKey as
    RSACryptoServiceProvider;



    result = rsa1.VerifyData(signSrc, sha, signDes);

    MessageBox.Show("valid: " + result);

    string expkey = Convert.ToBase64String(rsa.ExportCspBlob(true));

    txtExportedKey.Text = expkey;

    }
    =================================================

    Hope this helps some.

    Sincerely,

    Steven Cheng

    Microsoft MSDN Online Support Lead


    Delighting our customers is our #1 priority. We welcome your comments and
    suggestions about how we can improve the support we provide to you. Please
    feel free to let my manager know what you think of the level of service
    provided. You can send feedback directly to my manager at:
    .

    ==================================================
    Get notification to my posts through email? Please refer to
    http://msdn.microsoft.com/subscriptions/managednewsgroups/default.aspx#notif
    ications.

    Note: The MSDN Managed Newsgroup support offering is for non-urgent issues
    where an initial response from the community or a Microsoft Support
    Engineer within 1 business day is acceptable. Please note that each follow
    up response may take approximately 2 business days as the support
    professional working with you may need further investigation to reach the
    most efficient resolution. The offering is not appropriate for situations
    that require urgent, real-time or phone-based interactions or complex
    project analysis and dump analysis issues. Issues of this nature are best
    handled working with a dedicated Microsoft Support Engineer by contacting
    Microsoft Customer Support Services (CSS) at
    http://msdn.microsoft.com/subscriptions/support/default.aspx.
    ==================================================
    This posting is provided "AS IS" with no warranties, and confers no rights.

    --------------------
     
    Steven Cheng [MSFT], Jul 31, 2008
    #3
  4. Hi Peter,

    As you said that you want some information about verifying X509 certificate
    signature, I'd like to confirm what's the exact verification you want.

    My understanding is that you may have a X509 certificate which assocate
    with a publickey/private key pair( of RSA or DSA encypt provider) and
    you've also used the private key to digital signed some data, and want to
    verify the data, correct?

    If this is the case, generally you will need to do two things here:

    1. Retrieve the public/private key from the certificate (in certificate
    store of windows)

    2. use the key info associated with the certificate to do encryption or
    digital sign.

    Here are some web articles introducing some code on this:

    http://www.codeproject.com/KB/security/RSACryptoPad.aspx

    http://www.eggheadcafe.com/articles/20020630.asp

    and here is a simple test function I've written which include accessing
    cert store to retrieve key info in cert and do some RSA signing and
    verification:


    ======================================
    private void btnTest_Click(object sender, EventArgs e)
    {
    RSACryptoServiceProvider rsa;
    RSAParameters key;
    SHA1CryptoServiceProvider sha = new SHA1CryptoServiceProvider();

    bool result;


    signSrc = Encoding.UTF8.GetBytes("ABCDEFG");

    string tp = "2b6f8ac51a85cbaf429474a55304313968667611";
    X509Store store = new X509Store(StoreName.My,
    StoreLocation.CurrentUser);
    store.Open(OpenFlags.ReadOnly);

    X509Certificate2 cert2 =
    store.Certificates.Find(X509FindType.FindByThumbprint, tp, true)[0];

    store.Close();

    rsa = cert2.PrivateKey as RSACryptoServiceProvider;



    signDes = rsa.SignData(signSrc, sha);

    result = rsa.VerifyData(signSrc, sha, signDes);


    MessageBox.Show("valid: " + result);



    /** here try exporting the CERT to a exportable file */


    byte[] pfx_bytes =
    cert2.Export(X509ContentType.Pfx,"Password01!");


    //txtContent.Text = Convert.ToBase64String(pfx_bytes);


    X509Certificate2 filecert = new X509Certificate2();
    filecert.Import(pfx_bytes, "Password01!",
    X509KeyStorageFlags.DefaultKeySet);



    RSACryptoServiceProvider rsa1 = filecert.PrivateKey as
    RSACryptoServiceProvider;



    result = rsa1.VerifyData(signSrc, sha, signDes);

    MessageBox.Show("valid: " + result);

    string expkey = Convert.ToBase64String(rsa.ExportCspBlob(true));

    txtExportedKey.Text = expkey;

    }
    =================================================

    Hope this helps some.

    Sincerely,

    Steven Cheng

    Microsoft MSDN Online Support Lead


    Delighting our customers is our #1 priority. We welcome your comments and
    suggestions about how we can improve the support we provide to you. Please
    feel free to let my manager know what you think of the level of service
    provided. You can send feedback directly to my manager at:
    .

    ==================================================
    Get notification to my posts through email? Please refer to
    http://msdn.microsoft.com/subscriptions/managednewsgroups/default.aspx#notif
    ications.

    Note: The MSDN Managed Newsgroup support offering is for non-urgent issues
    where an initial response from the community or a Microsoft Support
    Engineer within 1 business day is acceptable. Please note that each follow
    up response may take approximately 2 business days as the support
    professional working with you may need further investigation to reach the
    most efficient resolution. The offering is not appropriate for situations
    that require urgent, real-time or phone-based interactions or complex
    project analysis and dump analysis issues. Issues of this nature are best
    handled working with a dedicated Microsoft Support Engineer by contacting
    Microsoft Customer Support Services (CSS) at
    http://msdn.microsoft.com/subscriptions/support/default.aspx.
    ==================================================
    This posting is provided "AS IS" with no warranties, and confers no rights.

    --------------------
     
    Steven Cheng [MSFT], Jul 31, 2008
    #4
  5. Hi Joe, I'm actually looking to verify the signature of a certificate. I
    have an X509Certificate2 object that has been signed with another
    certificate. As part of my verification of the source of the certificate,
    I'd like to verify that it has been signed by a known certificate.

    Thanks -- Peter
    --
    Browse http://connect.microsoft.com/VisualStudio/feedback/ and vote.
    http://www.peterRitchie.com/blog/
    Microsoft MVP, Visual Developer - Visual C#


     
    Peter Ritchie [C# MVP], Jul 31, 2008
    #5
  6. Hi Steven. It appears your sample code signs some data and verifies the
    signature on that data. The signed data I'm looking to verify is a
    certificate itself. Verifying a signature on data I've signed isn't an
    issue--with that sort of data I know what data to pass to Verify. With am
    X509Certificate2, if I wanted to use the Verify method, what data would I
    pass?

    Thanks -- Peter

    --
    Browse http://connect.microsoft.com/VisualStudio/feedback/ and vote.
    http://www.peterRitchie.com/blog/
    Microsoft MVP, Visual Developer - Visual C#


     
    Peter Ritchie [C# MVP], Jul 31, 2008
    #6
  7. Peter Ritchie [C# MVP]

    Joe Kaplan Guest

    I see what you are saying. What you really want to do is to build a chain
    for the certificate and validate that. Simply checking the signing
    certificate may not be adequate because something may have issed it as well.

    Try taking a peek at the X509Chain class and the Build method. Note that it
    will want you to apply a ChainPolicy as well where you describe what you are
    checking the cert for.

    Joe K.
    --
    Joe Kaplan-MS MVP Directory Services Programming
    Co-author of "The .NET Developer's Guide to Directory Services Programming"
    http://www.directoryprogramming.net
    --
     
    Joe Kaplan, Jul 31, 2008
    #7
  8. Thanks for your reply Peter,

    Now, I've got that you actually want to verify the signed certificate. As
    Joe has mentioned, this is something related to verify the certificate
    trust chain. You can have a look at the X509Chain class and Joe has also
    provided some suggestion that

    #X509Chain Class
    http://msdn.microsoft.com/en-us/library/system.security.cryptography.x509cer
    tificates.x509chain.aspx

    Sincerely,

    Steven Cheng

    Microsoft MSDN Online Support Lead


    Delighting our customers is our #1 priority. We welcome your comments and
    suggestions about how we can improve the support we provide to you. Please
    feel free to let my manager know what you think of the level of service
    provided. You can send feedback directly to my manager at:
    .

    ==================================================
    Get notification to my posts through email? Please refer to
    http://msdn.microsoft.com/subscriptions/managednewsgroups/default.aspx#notif
    ications.

    ==================================================
    This posting is provided "AS IS" with no warranties, and confers no rights.


    --------------------
     
    Steven Cheng [MSFT], Aug 1, 2008
    #8
  9. Peter Ritchie [C# MVP], Aug 5, 2008
    #9
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.