Hi
I thought I had successfully added some code I found to
encrypt/decrypt a string into my project.
I found the code in several places and it appeared that most people
thought it worked. It had been written by someone in TeamB too.
However, although it worked fine when i first added and compiled my
application, it seems to have developed an odd error with this function:
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;
When I try and debug my app that is using this unit the app now gives
me rangeccheck errors on this line:
Seed := (Byte(Result[I]) + Seed) * Word(C1) + Word(C2).
The original test project that I used to test the code still works
with no problems.
I have tried tracing through the original test app to get values to
compare with the new 'not working' app to track down the problem.
When the values are:
s='1301'
Key=33199
C1 = 52845;
C2 = 22719;
and I=1
In the working app I get:
(Byte(Result[I]) + Seed) * Word(C1) + Word(C2)=1763724594
and seed gets assigned 19762
while in my new app that raises an exception with 'range check
error'
My delphi help says that the range of a word is 0..65535, so I would
have thought neither example should run.
So I dont understand why this works, or why the test app assigns seed
a value of 19762 while my other app creates an exception.
I've tried posting on the Borland newsgroups in the hope that the chap
from teamB can explain it to me, but not had an answer.
If someone could spare a moment to point me in the direction of why
this works and what may be causing my problems I will be very
gratefull! :)
Cheers
Pete
This is the code:
unit uEncrypt;
interface
uses
sysutils;
function Decrypt(const S: AnsiString; Key: Word): AnsiString;
function Encrypt(const S: AnsiString; Key: Word): AnsiString;
function getpassword:string;
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;
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