' Объявляю структуры и функцию
Private Declare Function CertSetCertificateContextProperty Lib "crypt32" (ByRef pCertContext As Long, ByVal dwPropId As Long, ByVal dwFlags As Long, pvData As Any) As Long

Private Type CRYPT_KEY_PROV_PARAM
 dwParam As Long
 pbData As Long
 cbData As Long
 dwFlags As Long
End Type

Private Type CRYPT_KEY_PROV_INFO
    pwstringContainerName As String * 200
    pwstringProvName As String * 200
    longProvType As Long
    longFlags As Long
    longProvParam As Long
    rgProvParam As CRYPT_KEY_PROV_PARAM
    longKeySpec As Long
End Type

'Затем пробегаю по сертификатам, нахожу тех, которые без закрытого ключа, пытаюсь привязать ключ:
...
hCert = CertOpenSystemStore(0, "MY")
pCert = 0
    Do
        pCert = CertEnumCertificatesInStore(hCert, pCert)
        If (pCert <> 0) Then
            fResult = CertGetCertificateContextProperty(pCert, CERT_KEY_PROV_INFO_PROP_ID, 0, pcbData)
            If (fResult = 0) Then
                pvData = LocalAlloc(LPTR, pcbData)
                ProvInfo.pwstringContainerName = containerName
                ProvInfo.pwstringProvName = PROVIDER_NAME
                ProvInfo.longProvType = PROV_GOST_2001_DH
                ProvInfo.longFlags = 0
                ProvInfo.longProvParam = 0
                ProvInfo.longKeySpec = AT_KEYEXCHANGE
                If CertSetCertificateContextProperty(pCert, CERT_KEY_PROV_INFO_PROP_ID, 0, ProvInfo) <> 0 Then GoTo Hook
                MsgBox Err.LastDllError
            End If
        End If
    Loop While pCert <> 0
...

Private Type CRYPT_KEY_PROV_INFO
    pwstringContainerName As Long
    pwstringProvName As Long
    longProvType As Long
    longFlags As Long
    longProvParam As Long
    rgProvParam As Long
    longKeySpec As Long
End Type

Private Type CERT_CONTEXT
    dwCertEncodingType As Long
    pbCertEncoded As Long
    cbCertEncoded As Long
    pCertInfo As Long
    hCertStore As Long
End Type

Private Function CertInstall(containerName As String, Certificate As String) As Boolean

Dim hCP As Long
Dim hKey As Long
Dim pCert As Long
Dim provInfo As CRYPT_KEY_PROV_INFO
Dim a() As Byte
Dim b() As Byte
Dim c() As Byte
Dim hStore As Long
Dim Step As Integer

On Error GoTo Hook
    
    CertInstall = False
    Step = 0
    c = Certificate
    ' создать контекст сертификата
    Step = 1
    pCert = CertCreateCertificateContext(X509_ASN_ENCODING, VarPtr(c(0)), UBound(c) + 1)
    If pCert = 0 Then
        LogError "frmKeyChange: CertInstall. step = " & Step & ". dll error id = " & Err.LastDllError
        Exit Function
    End If
    ' заполнить инфу провайдера
    a = containerName
    b = PROVIDER_NAME
    provInfo.pwstringContainerName = VarPtr(a(0))
    provInfo.pwstringProvName = VarPtr(b(0))
    provInfo.longProvType = PROV_GOST_2001_DH
    provInfo.longFlags = 0
    provInfo.longProvParam = 0
    provInfo.longKeySpec = AT_KEYEXCHANGE
    ' ассоциировать сертификат с закрытым ключом
    Step = 2
    If CertSetCertificateContextProperty(pCert, CERT_KEY_PROV_INFO_PROP_ID, 0, provInfo) = 0 Then
        LogError "frmKeyChange: CertInstall. step = " & Step & ". dll error id = " & Err.LastDllError
        Call CertFreeCertificateContext(pCert)
        Exit Function
    End If
    ' запросить контекст контейнера закрытого ключа
    Step = 3
    If CryptAcquireContext(hCP, containerName, PROVIDER_NAME, PROV_GOST_2001_DH, 0) = 0 Then
        LogError "frmKeyChange: CertInstall. step = " & Step & ". dll error id = " & Err.LastDllError
        Call CertFreeCertificateContext(pCert)
        Call CryptReleaseContext(hCP, 0)
        Exit Function
    End If
    ' получить ссылку на пользовательский ключ
    Step = 4
    If CryptGetUserKey(hCP, AT_KEYEXCHANGE, hKey) = 0 Then
        LogError "frmKeyChange: CertInstall. step = " & Step & ". dll error id = " & Err.LastDllError
        Call CertFreeCertificateContext(pCert)
        Call CryptReleaseContext(hCP, 0)
        Exit Function
    End If
    ' записать сертификат в контейнер
    Step = 5
    If CryptSetKeyParam(hKey, KP_CERTIFICATE, VarPtr(c(0)), 0) = 0 Then
        LogError "frmKeyChange: CertInstall. step = " & Step & ". dll error id = " & Err.LastDllError
        Call CertFreeCertificateContext(pCert)
        Call CryptReleaseContext(hCP, 0)
        Exit Function
    End If
    ' добавить сертификат в личное хранилище
    Step = 6
    hStore = CertOpenSystemStore(0, "MY")
    Step = 7
    If CertAddCertificateContextToStore(hStore, pCert, CERT_STORE_ADD_ALWAYS, 0) = 0 Then
        LogError "frmKeyChange: CertInstall. step = " & Step & ". dll error id = " & Err.LastDllError
        Call CertFreeCertificateContext(pCert)
        Call CryptReleaseContext(hCP, 0)
        Call CertCloseStore(hStore, 0)
        Exit Function
    End If
    ' освободить ресурсы и уменьшить счетчик ссылок
    Step = 8
    Call CertCloseStore(hStore, 0)
    Call CertFreeCertificateContext(pCert)
    Call CryptReleaseContext(hCP, 0)
    CertInstall = True

Exit Function
Hook:
    LogError "frmKeyChange: CertInstall. step = " & Step & ". " & Err.description, eError
    CertInstall = False
End Function