CertGetCertificateContextProperty & CertSetCertificateContextProperty

Question

Hi,

I am trying to use CertGetCertificateContextProperty to get CERT_ROOT_PROGRAM_CERT_POLICIES_PROP_ID to read the OID's and use the CertSetCertificateContextProperty to add OID's that are missing.

I have imported the required DLL's.

Could someone provide sample code of how to get the values and put them in the structures. The CERT_POLICIES_INFO and CERT_POLICY_INFO structures have been defined. Also how do I use CryptDecodeObject and CryptEncodeObject.

Answer 1

This was placed under c# as c# was the programming language being used, please move back.

Answer 2

Hi Paul,

Is your issue about calling some Win32 functions via P/Invoke?
If so could you provide some code snippet for us to know your current progress?
Thanks for your understanding.

Have a nice day,

---

Leo Liu [MSFT]
MSDN Community Support | Feedback to us

Answer 3

Hi,

I can call the functions ok, just can't work out how to extract the data from the pointers. The documentation reads "Data type of pvData: A pointer to an array of BYTE values. The size of this array is specified in the pcbData parameter."

"Returns a pointer to an encoded CERT_POLICIES_INFO structure that contains the application policies...."

"This property can be decoded by using the CryptDecodeObject function..."

The CERT_POLICIES_INFO structure is only a size 16 but pcbData is 63 and this is what has confused me.

/// <summary>
/// The CERT_POLICIES_INFO structure contains an array of CERT_POLICY_INFO.
/// </summary>

[StructLayout ( LayoutKind . Sequential )]

public struct CERT_POLICIES_INFO
{
	/// <summary>
	/// Number of elements in the rgPolicyInfo array.
	/// </summary>
		
	public Int32 cPolicyInfo;
		
	/// <summary>
	/// Array of CERT_POLICY_INFO structures.
	/// </summary>
	/// <seealso cref="CERT_POLICY_INFO"/>
		
	public IntPtr rgPolicyInfo;
}

/// <summary>
/// The CERT_POLICY_INFO structure contains an object identifier (OID) specifying a policy and an optional array of policy qualifiers.
/// </summary>

[StructLayout ( LayoutKind . Sequential )]

public struct CERT_POLICY_INFO
{
	/// <summary>
	/// Object identifier (OID) string specifying the policy.
	/// </summary>

	[MarshalAs ( UnmanagedType . LPStr )]

	public string pszPolicyIdentifier;

	/// <summary>
	/// Number of elements in the rgPolicyQualifier array.
	/// </summary>

	public Int32 cPolicyQualifier;

	/// <summary>
	/// Array of CERT_POLICY_QUALIFIER_INFO structures.
	/// </summary>
	/// <seealso cref="CERT_POLICY_QUALIFIER_INFO"/>

	public IntPtr rgPolicyQualifier;
}

/// <summary>
/// The CertGetCertificateContextProperty function retrieves the information contained in an extended property of a certificate context.
/// </summary>
/// <param name="pCertContext">A pointer to the CERT_CONTEXT structure of the certificate that contains the property to be retrieved.</param>
/// <param name="dwPropId">The property to be retrieved.</param>
/// <param name="pvData">A pointer to a buffer to receive the data as determined by dwPropId.</param>
/// <param name="pcbData">A pointer to a DWORD value that specifies the size, in bytes, of the buffer pointed to by the pvData parameter.</param>
/// <returns>If the function succeeds, the function returns TRUE.</returns>

[DllImport ( "CRYPT32.DLL" , EntryPoint = "CertGetCertificateContextProperty" , CharSet = CharSet . Auto , SetLastError = true )]
[return: MarshalAs ( UnmanagedType . Bool )]
		
public static extern Boolean CertGetCertificateContextProperty ( [In] IntPtr pCertContext , [In] Int32 dwPropId , [Out] IntPtr pvData , [In , Out] ref Int32 pcbData );

/// <summary>
/// The CertSetCertificateContextProperty function sets an extended property for a specified certificate context.
/// </summary>
/// <param name="pCertContext">A pointer to a CERT_CONTEXT structure.</param>
/// <param name="dwPropId">The property to be set. The value of dwPropId determines the type and content of the pvData parameter.</param>
/// <param name="dwFlags">CERT_STORE_NO_CRYPT_RELEASE_FLAG can be set for the CERT_KEY_PROV_HANDLE_PROP_ID or CERT_KEY_CONTEXT_PROP_ID dwPropId properties.</param>
/// <param name="pvData">A pointer to a data type determined by the value of dwPropId.</param>
/// <returns>If the function succeeds, the function returns TRUE. If the function fails, the function returns FALSE. For extended error information, call GetLastError.</returns>

[DllImport ( "CRYPT32.DLL" , EntryPoint = "CertGetCertificateContextProperty" , CharSet = CharSet . Auto , SetLastError = true )]
public static extern Boolean CertSetCertificateContextProperty ( [In] IntPtr pCertContext , [In] Int32 dwPropId , [In] Int32 dwFlags , [In] IntPtr pvData );

if ( Imports . CertGetCertificateContextProperty ( hCertCntxt , Constants . CERT_ROOT_PROGRAM_CERT_POLICIES_PROP_ID , IntPtr . Zero , ref size ) )

Above is whats left of my code after trying diffrent things.

Answer 4

This issue has been resolved, I was miss understanding the documentation. What I needed to do was first Decode the Data to get the Policy Structure.