var
  Prov: HCRYPTPROV;
  hKey: HCRYPTKEY;
  X509Certificate: AnsiString;
begin
  if not CryptAcquireContext(Prov, PAnsiChar(ContainerName), PAnsiChar(CP_GR3410_2001_PROV_A), PROV_GOST_2001_DH, 0) then
    CryptoError('CryptAcquireContext');
  try
    if not CryptGetUserKey(Prov, AT_SIGNATURE, hKey) then
      CryptoError('CryptGetUserKey');

    // Как получить X509Certificate?
  finally
    CryptReleaseContext(Prov, 0);
  end;
end;