(Delphi DLL) RSA-OAEP with SHA256 hashing

RSA encrypt a SHA256 hash with OAEP padding.

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, StringBuilder, Rsa, PublicKey, JsonObject;

...

procedure TForm1.Button1Click(Sender: TObject);
var
pubkey: HCkPublicKey;
sbPem: HCkStringBuilder;
bCrlf: Boolean;
success: Boolean;
json: HCkJsonObject;
rsa: HCkRsa;
bUsePrivateKey: Boolean;
encryptedStr: PWideChar;

begin
// This example requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

pubkey := CkPublicKey_Create();

sbPem := CkStringBuilder_Create();
bCrlf := True;
CkStringBuilder_AppendLine(sbPem,'-----BEGIN PUBLIC KEY-----',bCrlf);
CkStringBuilder_AppendLine(sbPem,'MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA33TqqLR3eeUmDtHS89qF',bCrlf);
CkStringBuilder_AppendLine(sbPem,'3p4MP7Wfqt2Zjj3lZjLjjCGDvwr9cJNlNDiuKboODgUiT4ZdPWbOiMAfDcDzlOxA',bCrlf);
CkStringBuilder_AppendLine(sbPem,'04DDnEFGAf+kDQiNSe2ZtqC7bnIc8+KSG/qOGQIVaay4Ucr6ovDkykO5Hxn7OU7s',bCrlf);
CkStringBuilder_AppendLine(sbPem,'Jp9TP9H0JH8zMQA6YzijYH9LsupTerrY3U6zyihVEDXXOv08vBHk50BMFJbE9iwF',bCrlf);
CkStringBuilder_AppendLine(sbPem,'wnxCsU5+UZUZYw87Uu0n4LPFS9BT8tUIvAfnRXIEWCha3KbFWmdZQZlyrFw0buUE',bCrlf);
CkStringBuilder_AppendLine(sbPem,'f0YN3/Q0auBkdbDR/ES2PbgKTJdkjc/rEeM0TxvOUf7HuUNOhrtAVEN1D5uuxE1W',bCrlf);
CkStringBuilder_AppendLine(sbPem,'SwIDAQAB',bCrlf);
CkStringBuilder_AppendLine(sbPem,'-----END PUBLIC KEY-----',bCrlf);

// Load the public key object from the PEM. 
success := CkPublicKey_LoadFromString(pubkey,CkStringBuilder__getAsString(sbPem));
if (success <> True) then
  begin
    Memo1.Lines.Add(CkPublicKey__lastErrorText(pubkey));
    Exit;
  end;

// Build a small string to encrypt
json := CkJsonObject_Create();
CkJsonObject_UpdateString(json,'example','123');
CkJsonObject_UpdateString(json,'hello','world');
Memo1.Lines.Add(CkJsonObject__emit(json));

// This is the JSON to be RSA encrypted:  {"example":"123","hello":"world"}

// IMPORTANT: RSA encryption is only used to encrypt small amounts of data.
// RSA is only able to encrypt data to a maximum amount of your key size (2048 bits = 256 bytes) 
// minus padding / header data (11 bytes for PKCS#1 v1.5 padding, 42 bytes for OAEP).
// As a result it is often not possible to encrypt files with RSA directly. 
// RSA is also not meant for this purpose. 
// 
// If you want to encrypt more data, you can use something like:
// 1) Generate a 256-bit random keystring K
// 2) Encrypt your data with AES-CBC with K
// 3) Encrypt K with RSA
// 4) Send both to the other side 

rsa := CkRsa_Create();
CkRsa_putOaepPadding(rsa,True);
CkRsa_putOaepHash(rsa,'SHA-256');
CkRsa_ImportPublicKeyObj(rsa,pubkey);
CkRsa_putEncodingMode(rsa,'base64');

// Note: The OAEP padding uses random bytes in the padding, and therefore each time encryption happens,
// even using the same data and key, the result will be different --  but still valid.  One should not expect
// to get the same output.
bUsePrivateKey := False;
encryptedStr := CkRsa__encryptStringENC(rsa,CkJsonObject__emit(json),bUsePrivateKey);
if (CkRsa_getLastMethodSuccess(rsa) <> True) then
  begin
    Memo1.Lines.Add(CkRsa__lastErrorText(rsa));
    Exit;
  end;

Memo1.Lines.Add('Result: ' + encryptedStr);

CkPublicKey_Dispose(pubkey);
CkStringBuilder_Dispose(sbPem);
CkJsonObject_Dispose(json);
CkRsa_Dispose(rsa);

end;