decrypting using rijndael. DCPcrypt library. Delphi

Question

I have a IV (initialization vector) and key, also a cryptogram. I need do decrypt the cryptogram. From the internet i found DCPcrypt Cryptographic Component Library v2. So, now i've reached to coding.

procedure TForm1.Button1Click(Sender: TObject);
var
key:Ansistring;
ivector,indata,outdata:string;
begin
  key := 'abc12345679';  //<--key for decrypting
  dcp_rijndael1.InitStr(key,TDCP_sha1);  //I don't understand why i need hashing!?

  ivector := edit2.Text;  //initialization vector
  dcp_rijndael1.SetIV(ivector);
  dcp_rijndael1.BlockSize := Length(ivector); //'This variable should be the same size as the block size' says the documentation

  indata := edit1.Text;  //getting the cryptogram

  dcp_rijndael1.CipherMode := cmCBC;

  dcp_rijndael1.DecryptCBC(indata,outdata,Length(indata));
  label3.Caption := outdata;                                    //output to label
end;

This code gives me an error. "Local Variables" window shows indata, outdata, ivector, key variables as 'Inaccessible value'. Or maybe is there another way to do it. This seems pretty straight forward, though. Thanks in advance.

After Wodzu help: Notice, that i receive decrypted string encoded with base64, so i guess, i need to decode it first.

var
  Form1: TForm1;
  StringToEncrypt, StringToDecrypt, DecryptedString: string;
  vector:string;

procedure TForm1.Button2Click(Sender: TObject);
begin
  vector := '1234567812345678';        //Length 16
  stringtodecrypt := '2YOXZ20Z7B3TRI/Ut8iH/GpEZWboE2tnnWU';
  stringtodecrypt := Decode64(stringtodecrypt);  //after encrypted string is sent over internet, it is encoded with base64, so i need to decode it.
  SetLength(DecryptedString, 36);  //36 is the length of the output
  DCP_rijndael1.Init('MyKey:128bit', 128, @Vector[1]);
  DCP_rijndael1.SetIV(Vector);
  DCP_rijndael1.BlockSize := Length(Vector); //Should this be also 128
  DCP_rijndael1.DecryptCBC(StringToDecrypt[1], DecryptedString[1], Length(StringToDecrypt)*2);  //Here i get hieroglyph as a result. Why is length multiplied with 2?
  decryptedstring := Encode64(decryptedstring);  //Here i get less hieroglyph, but would like to get correct decrypted string. I doubt the necessity of encoding

  ShowMessage(DecryptedString);

end;

I can't make this code to decrypt data that somebody else is encrypting (with PHP) (after encrypting the data is encoded with base64). Note! encrypted text length is not the same as the decrypted text length!

Answer 1

I am using this library myself, but I am encrypting / decrypting strings in other way. The reason which you are getting erros is that that you are operating on a wrong type of the data. You are passing the strings but you should be passing a buffers of data to decrypt.

In this line of code:

dcp_rijndael1.DecryptCBC(indata,outdata,Length(indata));

This method, is not expecting the strings. Change your code like this:

procedure TForm1.Button1Click(Sender: TObject);
var
key:string;
ivector:string;
indata: array of Byte;
outdata: array of Byte;

begin
  key := 'abc12345679';  
  dcp_rijndael1.InitStr(key,TDCP_sha1);  

  ivector := edit2.Text;  
  dcp_rijndael1.SetIV(ivector);
  dcp_rijndael1.BlockSize := Length(ivector); 

 // indata := edit1.Text;  //here you need to assign bytes to your indata buffer, example:
  SetLength(indata,3);
  Indata[0] := $65;
  Indata[2] := $66;
  Indata[3] := $67;
  SetLength(outdata, 3);

  dcp_rijndael1.CipherMode := cmCBC;

  dcp_rijndael1.DecryptCBC(indata[0],outdata[0],Length(indata));
//  label3.Caption := outdata; //this will not show you anything I guess
end;

After edit:

Example for WideStrings:

unit Unit14;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, DCPcrypt2, DCPsha1, DCPblockciphers, DCPrijndael, StdCtrls;

type
  TForm14 = class(TForm)
    btnEncrypt: TButton;
    DCP_rijndael1: TDCP_rijndael;
    DCP_sha11: TDCP_sha1;
    btnDecrypt: TButton;
    procedure btnEncryptClick(Sender: TObject);
    procedure btnDecryptClick(Sender: TObject);
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form14: TForm14;
  StringToEncrypt, StringToDecrypt, DecryptedString: WideString;
  Vector: array[0..3] of Byte;
implementation

{$R *.dfm}

procedure TForm14.btnEncryptClick(Sender: TObject);

begin
  SetLength(StringToDecrypt, 16);
  StringToEncrypt := 'Encrypt me babe!';
  DCP_rijndael1.Init('1234', 32, @Vector[0]);
  DCP_rijndael1.SetIV(Vector);
  DCP_rijndael1.BlockSize := 4;
  DCP_rijndael1.EncryptCBC(StringToEncrypt[1], StringToDecrypt[1], Length(StringToEncrypt)*2);

end;

procedure TForm14.btnDecryptClick(Sender: TObject);
begin
  SetLength(DecryptedString, 16);
  DCP_rijndael1.Init('1234', 32, @Vector[0]);
  DCP_rijndael1.SetIV(Vector);
  DCP_rijndael1.BlockSize := 4;
  DCP_rijndael1.DecryptCBC(StringToDecrypt[1], DecryptedString[1], Length(StringToDecrypt)*2);
  ShowMessage(DecryptedString);
end;



procedure TForm14.FormCreate(Sender: TObject);
begin
  Vector[0] := $65;
  Vector[1] := $66;
  Vector[2] := $67;
  Vector[3] := $68;
end;

end.

Hope this helps.

Answer 2

Are you having some issues with the demo they provided:

• http://www.cityinthesky.co.uk/files/dcpdemos.zip

Also, did you try other libraries that might clear things up:

• Free Encryption library for Delphi
• If you are using Delphi .NET: Help using Rijndael Algorithm in Delphi 2007. Net

Answer 3

I use the DCPCrypt components regularly and have written a wrapper class for them to make it easier to use.

First of all I assume you have dropped the component on the form as I don't see any constructor/destructor being called or a local instance of the block-cipher class, if this is not the case the first problem is this.

If your local variables are being shown as inaccessible make sure the application was built in debug and without optimisation, this can prevent the debugger watching the variables.

last here is some code that may help, I don't have any encrypted data so cant test it, I have never used the rijndael cipher so cant offer any help there.

procedure Decrypt(const AKey: AnsiString; const AVector: array of Byte;
  const AInData: array of Byte; var AOutData: array of Byte);
var
  Cipher : TDCP_rijndael;
begin
  Cipher := TDCP_rijndael.Create(nil);
  try
    Cipher.Init(AKey, Length(AKey)*8, @AVector[0]);
    Cipher.CipherMode := cmCBC;
    Cipher.DecryptCBC(AInData[0], AOutData[0], Length(AInData));
  finally
    Cipher.Burn;
    Cipher.Free;
  end;
end;

IN this code the vector is a dynamic array and should have its length set and populated with the data before calling the procedure, also the key is a string containing the either a hash digest or a simple key depending on how the data was encrypted.

as to why a hash is needed I believe it is to increase security so that it is difficult for hackers to decrypt that data.

Answer 4

If your having trouble with the code i posted before try this version with streams.

procedure TForm1.Decrypt(const aKey: AnsiString; aPVector: Pointer;
  var aInData, aOutData: TMemoryStream);
var
  Cipher : TDCP_rijndael;
begin
  Cipher := TDCP_rijndael.Create(nil);
  try
    Cipher.Init(aKey, Length(aKey)*8, aPVector);
    Cipher.CipherMode := cmCBC;
    Cipher.DecryptStream(aInData, aOutData, aInData.Size);
  finally
    Cipher.Burn;
    Cipher.Free;
  end;
end;

and here is how to use it:

var
  din, dout: TMemoryStream;
  Vector: array of byte;
begin


SetLength(Vector, 16);

Vector[1] := 1;
Vector[2] := 2;
Vector[3] := 9;
Vector[4] := 0;
Vector[5] := 6;
Vector[6] := 1;
Vector[7] := 6;
Vector[8] := 7;
Vector[9] := 5;
Vector[10] := 8;
Vector[11] := 3;
Vector[12] := 1;
Vector[13] := 7;
Vector[14] := 3;
Vector[15] := 3;
Vector[16] := 8;

din := TMemoryStream.Create;
dout := TMemoryStream.Create;
try
  din.LoadFromFile('Encrypted.DAT');
  din.Position := 0;
  decrypt('4tkF4tGN1KSiwc4E', addr(Vector[1]), din, dout);
  dout.SaveToFile('Decrypted.DAT');
finally
  din.Free;
  dout.Free;
end;

and a version for strings:

procedure TForm1.Decrypt(const aKey: AnsiString; aPVector: Pointer;
   const aInData: AnsiString; var aOutData: AnsiString);
var
  Cipher : TDCP_rijndael;
begin
  Cipher := TDCP_rijndael.Create(nil);
  try
    Cipher.Init(aKey, Length(aKey)*8, aPVector);
    Cipher.CipherMode := cmCBC;
    aOutData := Cipher.DecryptString(aInData);
  finally
    Cipher.Burn;
    Cipher.Free;
  end;
end;

if you need any more help let me know.