Program.cs

var hStore = Libcapi.CertOpenSystemStoreA(IntPtr.Zero, "MY");
Console.WriteLine("hStore = {0}", hStore);
Console.WriteLine();

var pCertReceiver = Libcapi.CertFindCertificateInStore(
    hStore, Libcapi.X509_ASN_ENCODING | Libcapi.PKCS_7_ASN_ENCODING,
    0, Libcapi.CERT_FIND_SUBJECT_STR_A, "CRYPTO-PRO", IntPtr.Zero);
Console.WriteLine("certReceiver = {0}", pCertReceiver);
Console.WriteLine("GetLastError: {0} (0x{0:x})", Librdrsup.GetLastError());
Console.WriteLine();

var certReceiver = Marshal.PtrToStructure<Libcapi.CertContext>(pCertReceiver);
Console.WriteLine("certReceiver.hCertStore = {0}", certReceiver.hCertStore);
Console.WriteLine();

var certReceiverInfo = Marshal.PtrToStructure<Libcapi.CertInfo>(certReceiver.pCertInfo);
Console.WriteLine("receiver's alg id = {0}", certReceiverInfo.SignatureAlgorithm.pszObjId);
Console.WriteLine("receiver's pubk alg id = {0}", certReceiverInfo.SubjectPublicKeyInfo.Algorithm.pszObjId);
Console.WriteLine();

var pCertSender = Libcapi.CertFindCertificateInStore(
    hStore, Libcapi.X509_ASN_ENCODING | Libcapi.PKCS_7_ASN_ENCODING,
    0, Libcapi.CERT_FIND_SUBJECT_STR_A, "test@example.com", IntPtr.Zero);
Console.WriteLine("certSender = {0}", pCertSender);
Console.WriteLine("GetLastError: {0} (0x{0:x})", Librdrsup.GetLastError());
Console.WriteLine();

var certSender = Marshal.PtrToStructure<Libcapi.CertContext>(pCertSender);
Console.WriteLine("certSender.hCertStore = {0}", certSender.hCertStore);
Console.WriteLine();

var certSenderInfo = Marshal.PtrToStructure<Libcapi.CertInfo>(certSender.pCertInfo);
Console.WriteLine("sender's alg id = {0}", certSenderInfo.SignatureAlgorithm.pszObjId);
Console.WriteLine("sender's pubk alg id = {0}", certSenderInfo.SubjectPublicKeyInfo.Algorithm.pszObjId);
Console.WriteLine();

Console.WriteLine("CryptAcquireCertificatePrivateKey = {0}",
    Libcapi.CryptAcquireCertificatePrivateKey(
        pCertSender, 0, IntPtr.Zero,
        out var hSenderProv, out var senderKeySpec, out var callerFreeProv
    )
);
Console.WriteLine("GetLastError: {0} (0x{0:x})", Librdrsup.GetLastError());
Console.WriteLine($"hSenderProv = {hSenderProv}, keySpec = {senderKeySpec}, callerFreeProv = {callerFreeProv}");
Console.WriteLine();

Console.WriteLine("CryptGetUserKey = {0}",
    Libcapi.CryptGetUserKey(hSenderProv, senderKeySpec, out var hSenderPrivKey)
);
Console.WriteLine("hSenderPrivKey = {0}", hSenderPrivKey);
Console.WriteLine("GetLastError: {0} (0x{0:x})", Librdrsup.GetLastError());
Console.WriteLine();

Console.WriteLine("CryptImportPublicKeyInfoEx = {0}",
    Libcapi.CryptImportPublicKeyInfoEx(
        hSenderProv, Libcapi.X509_ASN_ENCODING | Libcapi.PKCS_7_ASN_ENCODING,
        ref certReceiverInfo.SubjectPublicKeyInfo, 0, 0, IntPtr.Zero,
        out var hReceiverPubKey
    )
);
Console.WriteLine("hReceiverPubKey = {0}", hReceiverPubKey);
Console.WriteLine("GetLastError: {0} (0x{0:x})", Librdrsup.GetLastError());
Console.WriteLine();

uint recPubKeyBlobLen = 256;
var recPubKeyBlob = Marshal.AllocHGlobal((int)recPubKeyBlobLen);
Console.WriteLine("CryptExportKey = {0}",
    Libcapi.CryptExportKey(
        hReceiverPubKey, IntPtr.Zero, Libcapi.PUBLICKEYBLOB, 0,
        recPubKeyBlob, ref recPubKeyBlobLen
    )
);
Console.WriteLine("recPubKeyBlobLen = {0}", recPubKeyBlobLen);
Console.WriteLine("GetLastError: {0} (0x{0:x})", Librdrsup.GetLastError());
Console.WriteLine();

Console.WriteLine("CryptImportKey = {0}",
    Libcapi.CryptImportKey(
        hSenderProv, recPubKeyBlob, recPubKeyBlobLen,
        hSenderPrivKey, 0, out var hAgreeKey
    )
);
Console.WriteLine("hAgreeKey = {0}", hAgreeKey);
Console.WriteLine("GetLastError: {0} (0x{0:x})", Librdrsup.GetLastError());
Console.WriteLine();

Console.WriteLine("CertCloseStore: {0}", Libcapi.CertCloseStore(hStore, 0));