AES-128 ECB decrypt example

[CC]

Hi,

as the title says it.
I have looked around but I could not find anything truly useful.

[lainz]

In other words Rijndael.

https://wiki.freepascal.org/DCPcrypt

Check that package, it has useful demos.

[trev]

You didn't look very far... this post for example.

[CC]

I have spent quite a few hours on this before asking and I did find the exact links provided here. Just figured that copy-pasting an example would be the least time consuming help. Faster then looking at my code. But here it is anyway. I know the format  the result should be, but it currently is gibberish.

The input length is 87.

Code: Pascal  [Select][+][-]

1. function TForm1.AES128_ECB_Decrypt(AString, aKey: string): string;
2. var
3.   inData  : TBytes;
4.   outData : TBytes;
5.   StreamSize: Int64;
6.   KeySizeInBytes, BlockSize: integer;
7.   inStream,outStream: TStringStream;   //inStream
8. begin
9.   inStream:= TStringStream.Create(AString);
10.   StreamSize:=  inStream.Size;
11.   outStream:= TStringStream.Create;
12.    try
13.      KeySizeInBytes:= 16;
14.      BlockSize:= KeySizeInBytes;
15.      SetLength(inData, BlockSize);
16.      SetLength(outData, BlockSize);
17.      //AES_Cipher := TDCP_rijndael.Create(nil); // already exists
18.      AES_Cipher.Init(aKey , 128, nil );
19.  
20.      While StreamSize > 0 do
21.      begin
22.        inStream.ReadBuffer(inData[0], BlockSize);
23.        AES_Cipher.DecryptECB(inData[0], outData[0]);
24.        outStream.WriteBuffer(outData[0], BlockSize);
25.        Log(inData);
26.        Log(outData);
27.        Dec(StreamSize, BlockSize);
28.        if StreamSize < KeySizeInBytes then  // Last block less then key size
29.        begin
30.           BlockSize:= StreamSize;
31.           SetLength(inData, BlockSize);
32.           SetLength(outData, BlockSize);
33.        end;
34.      end;
35.      result:= outStream.DataString;
36.    finally
37.      inStream.Free;
38.      outStream.Free;
39.    end;
40. end;                                

Result:

??M??.?I???RM?4?(%?=?6????ro?Id??m
??)\??
NO[??5??.????܊??r>?w𷋊xլ?k

[CC]

I still do not see what is wrong with the above code, but I got it working with mORMot lib SynCrypto.TAESECB.
It is higher level solution, only few lines of code to use it. Base64 decoding may be necessary  first though.