How do I call the default windows screen to choose a certificate? - windows

Question

THTTPRIO component, in HTTPWebNode property, when you click in ClientCertificate, Delphi opens a form to choose the certificate and load it's information in the component's propertys. Is this a windows screen? If it is, how can I use it? Today I'm using SecureBlackBox to load the certificates in a combobox, but I'd like to know if is possible to use this screen.
Thanks
UPDATE
I was able to show the dialog using the ms function CryptUIDlgSelectCertificateFromStore, using JWAPI. Now I'm having problems with the result of the function, the PCCERT_CONTEXT structure.
var
P: Pointer;
Context: PCCERT_CONTEXT;
Issuer: DATA_BLOB;
function GetDataBlobText(Data: DATA_BLOB): string;
begin
SetString(Result, PAnsiChar(Data.pbData), Data.cbData div SizeOf(AnsiChar));
end;
begin
P := CertOpenSystemStore(0, 'MY');
Context := CryptUIDlgSelectCertificateFromStore(P, 0, PChar('test'), nil, CRYPTUI_SELECT_ISSUEDTO_COLUMN, 0, nil);
if Context <> nil then
begin
Issuer := Context.pCertInfo.Issuer;
ShowMessage((GetDataBlobText(Issuer)));
end;
end;
The result in ShowMessage is:
UPDATE2
Thanks #RbMm.
To get string of ASN encoding fields (Issuer and Subject)
var
P: Pointer;
Context: PCCERT_CONTEXT;
Subject: DATA_BLOB;
SubjectStr: string;
size : Cardinal;
begin
P := CertOpenSystemStore(0, PAnsiChar('MY'));
Context := CryptUIDlgSelectCertificateFromStore(P, 0, 'test', 'select certificate',
CRYPTUI_SELECT_ISSUEDTO_COLUMN, 0, nil);
if Context <> nil then
begin
Subject := Context.pCertInfo.Subject;
size := CertNameToStr(X509_ASN_ENCODING or PKCS_7_ASN_ENCODING, #Subject, CERT_X500_NAME_STR, 0, 0);
SetString(SubjectStr, PAnsiChar(Subject.pbData), size);
CertNameToStr(X509_ASN_ENCODING or PKCS_7_ASN_ENCODING, #Subject, CERT_X500_NAME_STR, PAnsiChar(SubjectStr), size);
Result := SubjectStr;
end;
To get the string of raw data block (SerialNumber):
var
SerialNumber: CRYPT_INTEGER_BLOB;
size : Cardinal;
s: PWideChar;
ss: string;
begin
SerialNumber := Context.pCertInfo.SerialNumber;
CryptBinaryToStringW(SerialNumber.pbData, SerialNumber.cbData, CRYPT_STRING_HEX, nil, size);
s := AllocMem(SizeOf(Char) * size);
CryptBinaryToStringW(SerialNumber.pbData, SerialNumber.cbData, CRYPT_STRING_HEX, s, size);
ss := s;
showmessage(ss);
FreeMem(s, SizeOf(Char) * size);

Answer 1

all data blobs in certificate is encoded. so you need decode it. in general by using CryptDecodeObjectEx api. however for Issuer ( i.e. CERT_NAME_BLOB) decode you can use also CertNameToStrW. only after converts an encoded name in a CERT_NAME_BLOB structure to a null-terminated character string you can print it. code example on c/c++:
void PrintIssuer(PCCERT_CONTEXT Context)
{
CERT_NAME_BLOB Issuer = Context->pCertInfo->Issuer;
// option #1
if (ULONG len = CertNameToStrW(X509_ASN_ENCODING | PKCS_7_ASN_ENCODING, &Issuer, CERT_X500_NAME_STR, 0, 0))
{
PWSTR sz = (PWSTR)alloca( len * sizeof(WCHAR));
if (CertNameToStrW(X509_ASN_ENCODING | PKCS_7_ASN_ENCODING, &Issuer, CERT_X500_NAME_STR, sz, len))
{
DbgPrint("%S\n", sz);
}
}
// option #2
PCERT_NAME_INFO pcni;
ULONG size;
if (CryptDecodeObjectEx(X509_ASN_ENCODING | PKCS_7_ASN_ENCODING, X509_NAME, Issuer.pbData, Issuer.cbData,
CRYPT_DECODE_ALLOC_FLAG, 0, &pcni, &size))
{
if (DWORD cRDN = pcni->cRDN)
{
PCERT_RDN rgRDN = pcni->rgRDN;
do
{
if (DWORD cRDNAttr = rgRDN->cRDNAttr)
{
PCERT_RDN_ATTR rgRDNAttr = rgRDN->rgRDNAttr;
do
{
DbgPrint("ObjId = %s\n", rgRDNAttr->pszObjId);
switch (rgRDNAttr->dwValueType)
{
case CERT_RDN_PRINTABLE_STRING:
DbgPrint("Value = %s\n", rgRDNAttr->Value.pbData);
break;
}
} while (rgRDNAttr++, --cRDNAttr);
}
} while (rgRDN++, --cRDN);
}
LocalFree(pcni);
}
}
and output
CN=***
ObjId = 2.5.4.3
Value = ***
(the string after CN= and Value = is the same)
you can note that "2.5.4.3" is szOID_COMMON_NAME or "CN". so first api is append CN= before Issuer name. second variant return you name as is and additional ObjId = 2.5.4.3
convert SerialNumber to printable string can next way:
CRYPT_INTEGER_BLOB SerialNumber = Context->pCertInfo->SerialNumber;
DWORD cb = 0;
if (CryptBinaryToStringW(SerialNumber.pbData, SerialNumber.cbData, CRYPT_STRING_HEX, 0, &cb))
{
PWSTR sz = (PWSTR)alloca( cb * sizeof(WCHAR));
if (CryptBinaryToStringW(SerialNumber.pbData, SerialNumber.cbData, CRYPT_STRING_HEX, sz, &cb))
{
DbgPrint("%S\n", sz);
}
}