delphi - How can we connect with a website? Getting SSL error 1409442E

Question

I am using Delphi 10.2 Tokyo, trying to download some information from a web server.

I pass the command URL https://poloniex.com/public?command=returnCurrencies through this function using Indy 10.6.2.5366 (the command works if I paste it in a browser):

function ReadHTTPS(const url: string): string;
var
  IdHTTP: TIdHTTP;
  IdSSL: TIdSSLIOHandlerSocketOpenSSL;
begin
  IdHTTP := TIdHTTP.Create;
  try
    IdSSL := TIdSSLIOHandlerSocketOpenSSL.Create(IdHTTP);
    IdHTTP.IOHandler := IdSSL;
    result := IdHTTP.Get(url);
    if IdHTTP.ResponseText <> '' then
      OutputDebugString(PWideChar('ReadHTTPS: ' + IdHTTP.ResponseText));
  finally
    IdHTTP.Free;
  end;
end{ ReadHTTPS};

That gives the following error:

Error connecting with SSL. error:1409442E:SSL routines:ssl3_read_bytes:tlsv1 alert protocol version

I have tried installing the latest DLLs for OpenSSL in the same directory as the exe, but that didn't solve it.

Any ideas?

Answer 1

Make sure you are using an up-to-date version of the OpenSSL DLLs that support TLS v1.2 (the latest version that Indy currently supports is 1.0.2u), and then you need to enable the sslvTLSv1_2 flag in the SSLIOHandler's SSLOptions.SSLVersions property:

IdSSL.SSLOptions.SSLVersions := [sslvTLSv1, sslvTLSv1_1, sslvTLSv1_2];

Or:

IdSSL.SSLOptions.SSLVersions := [sslvTLSv1_2];

Indy enables only TLS v1.0 by default, and apparently https://poloniex.com does not allow TLS versions prior to TLS v1.2.