(Delphi DLL) Convert RSA Private Key to Public Key

Demonstrates how to get a public RSA key from a private RSA key.

Chilkat for Delphi Downloads Chilkat non-ActiveX DLL for Delphi Chilkat ActiveX DLL for Delphi * The examples here use the non-ActiveX DLL.

uses
    Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
    Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, PrivateKey, PublicKey;

...

procedure TForm1.Button1Click(Sender: TObject);
var
key: HCkPrivateKey;
success: Boolean;
pubKey: HCkPublicKey;
bPreferPkcs1: Boolean;

begin
key := CkPrivateKey_Create();

// Step 1: Load the private key from a source.
// (Chilkat can load private keys from all types of formats, and from in-memory bytes or encoded strings.
// see the online reference documentation for more options.)
success := CkPrivateKey_LoadPemFile(key,'qa_data/pem/VP_Private.pem');
if (success <> True) then
  begin
    Memo1.Lines.Add(CkPrivateKey__lastErrorText(key));
    Exit;
  end;

// Step 2: Get the public key object from the private key object.
pubKey := CkPrivateKey_GetPublicKey(key);
if (CkPrivateKey_getLastMethodSuccess(key) <> True) then
  begin
    Memo1.Lines.Add(CkPrivateKey__lastErrorText(key));
    Exit;
  end;

// Step 3: Save the public key in a desired format. 
// (Chilkat can load or save public and private keys in many different formats.  See
// the online reference documentation for more options.)

// Saves to a PKCS8 PEM file.
bPreferPkcs1 := False;
success := CkPublicKey_SavePemFile(pubKey,bPreferPkcs1,'qa_data/pem/VP_Public.pem');
if (CkPublicKey_getLastMethodSuccess(pubKey) <> True) then
  begin
    Memo1.Lines.Add(CkPublicKey__lastErrorText(pubKey));
    Exit;
  end;

CkPublicKey_Dispose(pubKey);

Memo1.Lines.Add('Extracted and saved public key from private key.');

CkPrivateKey_Dispose(key);

end;