How can I get CSR from signature key pair - c++

Question

Based on this tutorial, I have successfully created the signature key pair and Key Container.
The key container after creation will be stored in %AppData%\Roaming\Microsoft\Crypto\RSA folder.
Next, I want to use signature key pair to get CSR(certificate signing request). So how do I do this?
Thanks in advance.

Answer 1

Get NCRYPT_KEY_HANDLE key handle with NCryptOpenKey if use CNG
(or get HCRYPTPROV handle with CryptAcquireContext if use CAPI);
Export public key with CryptExportPublicKeyInfo;
Encode subject name with CertStrToName, for example:
DWORD EncodeCertificateName(const std::wstring& name_to_encode, const DWORD delim_flag,
std::vector<BYTE>& encoded_name)
{
DWORD encoded_name_len = 0;
/* get length */
if (!CertStrToName(X509_ASN_ENCODING | PKCS_7_ASN_ENCODING,
name_to_encode.data(),
CERT_X500_NAME_STR | delim_flag,
NULL,
NULL,
&encoded_name_len,
NULL))
{
return GetLastError();
}
encoded_name.resize(encoded_name_len);
/* encode */
if (!CertStrToName(X509_ASN_ENCODING | PKCS_7_ASN_ENCODING,
name_to_encode.data(),
CERT_X500_NAME_STR | delim_flag,
NULL,
encoded_name.data(),
&encoded_name_len,
NULL))
{
return GetLastError();
}
return ERROR_SUCCESS;
}
std::wstring subject = L"CN=Test_request, E=test#test.com";
std::vector<BYTE> encoded_name;
EncodeCertificateName(subject, CERT_NAME_STR_COMMA_FLAG, &encoded_name);
Fill CERT_REQUEST_INFO structure:
CERT_REQUEST_INFO cert_req_info;
/* set attributes if any */
cert_req_info.cAttribute = 0;
cert_req_info.rgAttribute = nullptr;
cert_req_info.dwVersion = CERT_REQUEST_V1;
/* set encoded subject name */
cert_req_info.Subject.cbData = static_cast<DWORD>(name_enc.size());
cert_req_info.Subject.pbData = name_enc.data();
/* set exported public key info */
cert_req_info.SubjectPublicKeyInfo = pub_key_info;
Fill CRYPT_ALGORITHM_IDENTIFIER structure:
CRYPT_ALGORITHM_IDENTIFIER sig_alg;
/* set signature algorithm, for example */
sig_alg.pszObjId = szOID_RSA_SHA256RSA;
Create certificate request with CryptSignAndEncodeCertificate and parameter lpszStructType = X509_CERT_REQUEST_TO_BE_SIGNED:
std::vector<BYTE> enc_req_val;
DWORD enc_req_len = 0;
/* get length */
if (!CryptSignAndEncodeCertificate(hProv,
AT_SIGNATURE,
PKCS_7_ASN_ENCODING | X509_ASN_ENCODING,
X509_CERT_REQUEST_TO_BE_SIGNED,
&cert_req_info,
&sig_alg,
nullptr,
nullptr,
&enc_req_len))
{
/* handle error */
}
enc_req_val.resize(enc_req_len);
/* create certificate request */
if (!CryptSignAndEncodeCertificate(hProv,
AT_SIGNATURE,
PKCS_7_ASN_ENCODING | X509_ASN_ENCODING,
X509_CERT_REQUEST_TO_BE_SIGNED,
&cert_req_info,
&sig_alg,
nullptr,
enc_req_val.data(),
&enc_req_len))
{
/* handle error */
}