Delphi DLL

RSA Encryption -- Same Key Different Results

See more RSA Examples

The RSA encryption algorithm produces different results for each call, even when encrypting the same data with the same key. Decryption however, will produce the correct results. This example demonstrates.

*** The reason this occurs is that RSA encryption uses PKCS1 v1.5 padding, and this padding scheme uses random bytes. It is random bytes in the padding that causes the result to be different each time.

Delphi DLL

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

...

procedure TForm1.Button1Click(Sender: TObject);
var
success: Boolean;
rsa: HCkRsa;
pubKeyXml: PWideChar;
privKeyXml: PWideChar;
pubKey: HCkPublicKey;
privKey: HCkPrivateKey;
plainText: PWideChar;
usePrivateKey: Boolean;
encryptedStr1: PWideChar;
encryptedStr2: PWideChar;
rsa2: HCkRsa;
decryptedStr1: PWideChar;
decryptedStr2: PWideChar;

begin
success := False;

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

rsa := CkRsa_Create();

pubKeyXml := '<RSAPublicKey><Modulus>xxyv1RDPU0MvfFIIa98HppXdcuI7zSu8uIqyGAy/VoxPvxZFX0acajznvjVRHipHbpcO6ryo2LwXUPf89qOqLb3Qd1lfD2ZnH+TQ6MZXNxfFRxTpTUd+tTR4EBYpd2t6kzq8ZRJYLdlviaMQQqUEwR54k7Op5HJYVKUcHIkP1xE=</Modulus><Exponent>AQAB</Exponent></RSAPublicKey>';

privKeyXml := '<RSAKeyValue><Modulus>xxyv1RDPU0MvfFIIa98HppXdcuI7zSu8uIqyGAy/VoxPvxZFX0acajznvjVRHipHbpcO6ryo2LwXUPf89qOqLb3Qd1lfD2ZnH+TQ6MZXNxfFRxTpTUd+tTR4EBYpd2t6kzq8ZRJYLdlviaMQQqUEwR54k7Op5HJYVKUcHIkP1xE=</Modulus><Exponent>AQAB</Exponent><P>4cpW9fvG99Jsz8/AO7PDHTl+pPRAglksrR2kClLV2g9DEeFe/bvmCxLUgMCJ+0eGQ1zA6aA7McKr13zTQ7jKpQ==</P><Q>4cCS/kFlq/P1ExF37Fkh4pCodOEGutepLEG7Q/KljT3ZGlAY+2l8fGu4f+hrkUuGoFl7NOMaJflULoPIgQaq/Q==</Q><DP>lkjcSsvzqh3YKRXJiLNkyf3rypV8noYGU4+oEOsDxilkZfFRDafUPUiiQrRk4ui/d/SzvozU+ZDuWfaOk8PatQ==</DP><DQ>SYCD25i7W8Mwdibn3uIecEAdOQDTSh5RjIFSUYs9b8FFYJXXrHPp/jCsf6jS7RmkGa1Iui1/JAIL8KEjtS7QmQ==</DQ><InverseQ>EDAJa3TpNdPQ3GIdBpnTgFTQY5A60DcszsUW/iCYoXQdPVJ9BLBxVTe9jiLzGuNuzLkVBwQlCy0Bf84hACRV9A==</InverseQ><D>cMFdDYKkddlRNczaugOmOH8b1egpx2liSPs6GYZ2gFObAXJiPK8m+r6c2ckls7hrlUP0DZhi4cG6Tn7xANb0Ek17P7QquVhQYOmFy/YHzm+IJbcwwq7pJHhZBhtcjyXqfUZ+BADGE//GQbrSVwVltpOj5KcxG88NAprLn2MMxfE=</D></RSAKeyValue>';

pubKey := CkPublicKey_Create();
success := CkPublicKey_LoadFromString(pubKey,pubKeyXml);
if (success = False) then
  begin
    Memo1.Lines.Add(CkPublicKey__lastErrorText(pubKey));
    Exit;
  end;

privKey := CkPrivateKey_Create();
success := CkPrivateKey_LoadXml(privKey,privKeyXml);
if (success = False) then
  begin
    Memo1.Lines.Add(CkPrivateKey__lastErrorText(privKey));
    Exit;
  end;

success := CkRsa_UsePublicKey(rsa,pubKey);
if (success = False) then
  begin
    Memo1.Lines.Add(CkRsa__lastErrorText(rsa));
    Exit;
  end;

// Encrypt a string and return the encrypted data base64-encoded:
CkRsa_putEncodingMode(rsa,'base64');

plainText := 'RSA gives different results with each call, weird but OK';

usePrivateKey := False;
encryptedStr1 := CkRsa__encryptStringENC(rsa,plainText,usePrivateKey);
Memo1.Lines.Add(encryptedStr1);

// Do it again. The results are different...
encryptedStr2 := CkRsa__encryptStringENC(rsa,plainText,usePrivateKey);
Memo1.Lines.Add(encryptedStr2);

// Now decrypt both strings, and the results are correct
// in both cases:
rsa2 := CkRsa_Create();
success := CkRsa_UsePrivateKey(rsa2,privKey);
if (success = False) then
  begin
    Memo1.Lines.Add(CkRsa__lastErrorText(rsa));
    Exit;
  end;

CkRsa_putEncodingMode(rsa2,'base64');
usePrivateKey := True;

decryptedStr1 := CkRsa__decryptStringENC(rsa2,encryptedStr1,usePrivateKey);
Memo1.Lines.Add(decryptedStr1);

decryptedStr2 := CkRsa__decryptStringENC(rsa2,encryptedStr2,usePrivateKey);
Memo1.Lines.Add(decryptedStr2);

CkRsa_Dispose(rsa);
CkPublicKey_Dispose(pubKey);
CkPrivateKey_Dispose(privKey);
CkRsa_Dispose(rsa2);

end;