Category : Utilities for DOS and Windows Machines
Archive   : CODEIT.ZIP
Filename : DECODEIT.PAS

Program DECODEIT;
Const
MaxBuf = 30000;
Var
Password : String[6];
seed1, seed2, seed1x, seed2x : Byte;
source, dest : File;
buffer : Array [1..MaxBuf] of Byte;
BytesRead : Real;
i : Integer;

(********************************************************************)

Procedure OpenFiles;
Const
s : Array [1..6] Of Char = ('L','O','C','K','E','D');
Begin
Assign(source,ParamStr(1));
(*$I-*)
Reset(source,1);
(*$I+*)
If IOResult <> 0 Then
Begin
Writeln('File not found.');
Halt;
End;

BlockRead(source,buffer,6);
If Not ((buffer[1] = ord('L')) And
(buffer[2] = ord('O')) And
(buffer[3] = ord('C')) And
(buffer[4] = ord('K')) And
(buffer[5] = ord('E')) And
(buffer[6] = ord('D'))) Then
Begin
Writeln('File is not locked.');
Halt;
End;

BlockRead(source,Seed1x, 1);
BlockRead(source,Seed2x, 1);

If ((seed1 <> Seed1x) OR (seed2 <> Seed2x)) Then
Begin
Writeln('Wrong Password.');
Halt;
End;

Assign(dest,'$$$$$.$$');
Rewrite(dest,1);

End;

(****************************************************************)

Procedure GetSeed;
Var
i, j : Integer;
Begin
Seed1 := 0;
Seed2 := 0;
Password := ParamStr(2);

j := Length(Password);
For i:= 1 to Length(Password) Do
Begin
Seed1 := Seed1 + (Ord(Password[i]) * i);
Seed2 := Seed2 + (Ord(Password[i]) * i);
j := j - 1;
End;
End;

(*****************************************************************)

Procedure DecodeFiles;
Var
i1, i2 : Byte;
rr : Integer;
Begin
i1 := Seed1;
i2 := Seed2;
BytesRead := 0;
BlockRead(source, buffer, MaxBuf, rr);
BytesRead := BytesRead + rr;
While rr > 0 Do
Begin
For i := 1 to rr Do
Begin
i1 := i1 - i;
i2 := i2 +i;
If odd(i) Then
buffer[i] := buffer[i] + i1
Else
buffer[i] := buffer[i] - i2;
End;
BlockWrite(dest, buffer, rr);
BlockRead(source, buffer, MaxBuf, rr);
BytesRead := BytesRead + rr;
End;
End;

(*******************************************************************)

Procedure CloseFiles;
Var
i : Integer;
Begin
Rewrite(source, 1);
FillChar(buffer, MaxBuf, 0);
While BytesRead > 0 Do
Begin
If BytesRead > MaxBuf Then
BlockWrite(source, buffer, MaxBuf)
Else
Begin
i := Trunc(BytesRead);
BlockWrite(source, buffer, i);
End;
BytesRead := BytesRead - MaxBuf;
End;
Close(source);
Close(dest);
Erase(source);
Rename(dest, ParamStr(1));
End;

(***************************************************************)


Begin
If Paramcount <> 2 Then
Begin
Writeln('Syntax: DECODEIT Filename password');
Halt;
End;
Getseed;
OpenFiles;
DecodeFiles;
CloseFiles;
End.