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Encrypt and decrypt functions

   

Here is some code that you can use in a .pas file that was written using encryption. Save this information to a unit called UEncrypt.pas.

The key here is creating a Seed Key.

unit UEncrypt;

interface

function Decrypt(const S: AnsiString; Key: Word): AnsiString;
function Encrypt(const S: AnsiString; Key: Word): AnsiString;

implementation

const
  C1 = 52845;
  C2 = 22719;

function Decode(const S: AnsiString): AnsiString;
const
  Map: array[Char] of Byte = (0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 62, 0, 0, 0, 63, 52, 53,
    54, 55, 56, 57, 58, 59, 60, 61, 0, 0, 0, 0, 0, 0, 0, 0, 1, 2,
    3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19,
    20, 21, 22, 23, 24, 25, 0, 0, 0, 0, 0, 0, 26, 27, 28, 29, 30,
    31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45,
    46, 47, 48, 49, 50, 51, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0
  );
var
  I: LongInt;
begin
  case Length(S) of
    2:
    begin
      I := Map[S[1]] + (Map[S[2]] shl 6);
      SetLength(Result, 1);
      Move(I, Result[1], Length(Result))
    end;
    3:
    begin
      I := Map[S[1]] + (Map[S[2]] shl 6) + (Map[S[3]] shl 12);
      SetLength(Result, 2);
      Move(I, Result[1], Length(Result))
    end;
    4:
    begin
      I := Map[S[1]] + (Map[S[2]] shl 6) + (Map[S[3]] shl 12) +
        (Map[S[4]] shl 18);
      SetLength(Result, 3);
      Move(I, Result[1], Length(Result))
    end;
  end;
end;

function PreProcess(const S: AnsiString): AnsiString;
var
  SS: AnsiString;
begin
  SS := S;
  Result := '';
  while SS <> '' do
  begin
    Result := Result + Decode(Copy(SS, 1, 4));
    Delete(SS, 1, 4)
  end;
end;

function InternalDecrypt(const S: AnsiString; Key: Word): AnsiString;
var
  I: Word;
  Seed: Word;
begin
  Result := S;
  Seed := Key;
  for I := 1 to Length(Result) do
  begin
    Result[I] := Char(Byte(Result[I]) xor (Seed shr 8));
    Seed := (Byte(S[I]) + Seed) * Word(C1) + Word(C2)
  end;
end;

function Decrypt(const S: AnsiString; Key: Word): AnsiString;
begin
  Result := InternalDecrypt(PreProcess(S), Key)
end;

function Encode(const S: AnsiString): AnsiString;
const
  Map: array[0..63] of Char = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ' +
    'abcdefghijklmnopqrstuvwxyz0123456789+/';
var
  I: LongInt;
begin
  I := 0;
  Move(S[1], I, Length(S));
  case Length(S) of
    1:
      Result := Map[I mod 64] + Map[(I shr 6) mod 64];
    2:
      Result := Map[I mod 64] + Map[(I shr 6) mod 64] +
        Map[(I shr 12) mod 64];
    3:
      Result := Map[I mod 64] + Map[(I shr 6) mod 64] +
        Map[(I shr 12) mod 64] + Map[(I shr 18) mod 64]
  end;
end;

function PostProcess(const S: AnsiString): AnsiString;
var
  SS: AnsiString;
begin
  SS := S;
  Result := '';
  while SS <> '' do
  begin
    Result := Result + Encode(Copy(SS, 1, 3));
    Delete(SS, 1, 3)
  end;
end;

function InternalEncrypt(const S: AnsiString; Key: Word): AnsiString;
var
  I: Word;
  Seed: Word;
begin
  Result := S;
  Seed := Key;
  for I := 1 to Length(Result) do
  begin
    Result[I] := Char(Byte(Result[I]) xor (Seed shr 8));
    Seed := (Byte(Result[I]) + Seed) * Word(C1) + Word(C2)
  end;
end;

function Encrypt(const S: AnsiString; Key: Word): AnsiString;
begin
  Result := PostProcess(InternalEncrypt(S, Key))
end;

end.

To demonstrate, create a windows form with three TMemo controls and a TButton and add a button click event handler as follows:

uses
  ...  
  UEncrypt;
...
procedure TForm1.Button1Click(Sender: TObject);
const
  SeedKey = 53269;
begin
  Memo2.Text := Encrypt(Memo1.Text,SeedKey);
  Memo3.Text := Decrypt(Memo2.Text,SeedKey);
end;

Enter some text to be converted into Memo1. Click the button. The encrypted code appears in Memo2 and the decrypted code in Memo3.

The demo code and narrative have been tweaked a little.

Author: Steve Schafer
Added: 2009-06-23
Last updated: 2009-08-11

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