Mega Code Archive
How to Encrypt Decrypt a String
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Title: How to Encrypt/ Decrypt a String
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.
{**************************************************************}
// Example:
{**************************************************************}
procedure TForm1.Button1Click(Sender: TObject);
const
my_key = 33189;
var
sEncrypted, sDecrypted :AnsiString;
begin
// Encrypt a string
sEncrypted := Encrypt('this is a sample text to encrypt...abcd 123 {}[]?=)=(',my_key);
// Show encrypted string
ShowMessage(sEncrypted);
// Decrypt the string
sDecrypted := Decrypt(sEncrypted,my_key);
// Show decrypted string
ShowMessage(sDecrypted);
end;
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