DataFlex

Get Certificate As XML (and gets Signature Algorithm Identifier)

Demonstrates how to convert a certificate to XML such that the contents can easily be identified and accessed. Typically, the Chilkat Cert API provides properties and methods to access the most commonly needed pieces of information from a certificate. If a bit of information is not readily available then it can likely be retrieved from the XML representation. One such case is the certificate's signature algorithm identifier.

The basic internal format of a certificate is as follows (from section 4.1 of RFC 5280).

   Certificate  ::=  SEQUENCE  {
        tbsCertificate       TBSCertificate,
        signatureAlgorithm   AlgorithmIdentifier,
        signatureValue       BIT STRING  }

   TBSCertificate  ::=  SEQUENCE  {
        version         [0]  EXPLICIT Version DEFAULT v1,
        serialNumber         CertificateSerialNumber,
        signature            AlgorithmIdentifier,
        issuer               Name,
        validity             Validity,
        subject              Name,
        subjectPublicKeyInfo SubjectPublicKeyInfo,
        issuerUniqueID  [1]  IMPLICIT UniqueIdentifier OPTIONAL,
        subjectUniqueID [2]  IMPLICIT UniqueIdentifier OPTIONAL,
                             -- If present, version MUST be v2 or v3
        extensions      [3]  EXPLICIT Extensions OPTIONAL
                             -- If present, version MUST be v3
        }

Chilkat does not expect you to fully understand this notation and structure, but you can see that at a high level, the certificate is a sequence of three things, one after the other (a TBSCertifciate, an AlgorithmIdentifier, and a BIT STRING that is the signature). In XML format, it will look like this:

<sequence>
    <sequence>
        TBSCertificate goes here...
    </sequence>
    <sequence>
        <oid>1.2.840.113549.1.1.11</oid>
        <null />
    </sequence>
    <bits n="2048">3D20E895... 8DA307EC</bits>
</sequence>

The "oid" specifies the signature algorithm (such as sha256RSA), but it is an OID. In this case, the OID "1.2.840.113549.1.1.11" indicates "sha256WithRSAEncryption". (Google "1.2.840.113549.1.1.11" and you will find the 1st search result is http://www.alvestrand.no/objectid/1.2.840.113549.1.1.11.html. You can lookup any OID this way, to see what it means.)

DataFlex

Use ChilkatAx-win32.pkg

Procedure Test
    Boolean iSuccess
    Handle hoSocket
    Boolean iUseTls
    Integer iMaxWaitMillisec
    String sTlsServerHost
    Variant vCert
    Handle hoCert
    String sCertXml
    Handle hoXml
    Variant vAlgId
    Handle hoAlgId
    String sOid
    String sTemp1

    Move False To iSuccess

    // This example assumes the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    Get Create (RefClass(cComChilkatSocket)) To hoSocket
    If (Not(IsComObjectCreated(hoSocket))) Begin
        Send CreateComObject of hoSocket
    End

    Move True To iUseTls
    Move 20000 To iMaxWaitMillisec
    Move "www.google.com" To sTlsServerHost

    Get ComConnect Of hoSocket sTlsServerHost 443 iUseTls iMaxWaitMillisec To iSuccess
    If (iSuccess = False) Begin
        Get ComLastErrorText Of hoSocket To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    Get Create (RefClass(cComChilkatCert)) To hoCert
    If (Not(IsComObjectCreated(hoCert))) Begin
        Send CreateComObject of hoCert
    End
    Get pvComObject of hoCert to vCert
    Get ComGetServerCert Of hoSocket vCert To iSuccess
    If (iSuccess = False) Begin
        Get ComLastErrorText Of hoSocket To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    // Close the connection with the server
    // Wait a max of 20 millsec for a clean TLS shutdown.  
    Get ComClose Of hoSocket 20 To iSuccess

    // Examine the server cert in XML format
    Get ComExportCertXml Of hoCert To sCertXml
    Showln sCertXml

    // Let's parse the XML to get the signature algorithm identifier.
    Get Create (RefClass(cComChilkatXml)) To hoXml
    If (Not(IsComObjectCreated(hoXml))) Begin
        Send CreateComObject of hoXml
    End
    Get ComLoadXml Of hoXml sCertXml To iSuccess

    // The 2nd child is at index 1.
    Get ComGetChild Of hoXml 1 To vAlgId
    If (IsComObject(vAlgId)) Begin
        Get Create (RefClass(cComChilkatXml)) To hoAlgId
        Set pvComObject Of hoAlgId To vAlgId
    End
    Get ComGetChildContent Of hoAlgId "oid" To sOid
    Showln "Signature Algorithm OID = " sOid

    Send Destroy of hoAlgId


End_Procedure