Оформил: DeeCo
Автор: http://www.swissdelphicenter.ch

unit EZCrypt;

 {modeled by Ben Hochstrasser(bhoc@surfeu.ch) after some code snippet from borland}

 interface

 uses Windows, Classes;

 type
   TWordTriple = Array[0..2] of Word;

 function FileEncrypt(InFile, OutFile: String; Key: TWordTriple): boolean;
 function FileDecrypt(InFile, OutFile: String; Key: TWordTriple): boolean;
 function TextEncrypt(const s: string; Key: TWordTriple): string;
 function TextDecrypt(const s: string; Key: TWordTriple): string;
 function MemoryEncrypt(Src: Pointer; SrcSize: Cardinal; Target: Pointer; TargetSize: Cardinal; Key: TWordTriple): boolean;
 function MemoryDecrypt(Src: Pointer; SrcSize: Cardinal; Target: Pointer; TargetSize: Cardinal; Key: TWordTriple): boolean;

 implementation

 function MemoryEncrypt(Src: Pointer; SrcSize: Cardinal; Target: Pointer; TargetSize: Cardinal; Key: TWordTriple): boolean;
 var
   pIn, pOut: ^byte;
   i : Cardinal;
 begin
   if SrcSize = TargetSize then
   begin
     pIn := Src;
     pOut := Target;
     for i := 1 to SrcSize do
     begin
       pOut^ := pIn^ xor (Key[2] shr 8);
       Key[2] := Byte(pIn^ + Key[2]) * Key[0] + Key[1];
       inc(pIn);
       inc(pOut);
     end;
     Result := True;
   end else
     Result := False;
 end;

 function MemoryDecrypt(Src: Pointer; SrcSize: Cardinal; Target: Pointer; TargetSize: Cardinal; Key: TWordTriple): boolean;
 var
   pIn, pOut: ^byte;
   i : Cardinal;
 begin
   if SrcSize = TargetSize then
   begin
     pIn := Src;
     pOut := Target;
     for i := 1 to SrcSize do
     begin
       pOut^ := pIn^ xor (Key[2] shr 8);
       Key[2] := byte(pOut^ + Key[2]) * Key[0] + Key[1];
       inc(pIn);
       inc(pOut);
     end;
     Result := True;
   end else
     Result := False;
 end;

 function TextCrypt(const s: string; Key: TWordTriple; Encrypt: Boolean): string;
 var
   bOK: Boolean;
 begin
   SetLength(Result, Length(s));
   if Encrypt then
     bOK := MemoryEncrypt(PChar(s), Length(s), PChar(Result), Length(Result), Key)
   else
     bOK := MemoryDecrypt(PChar(s), Length(s), PChar(Result), Length(Result), Key);
   if not bOK then Result := '';
 end;

 function FileCrypt(InFile, OutFile: String; Key: TWordTriple; Encrypt: Boolean): boolean;
 var
   MIn, MOut: TMemoryStream;
 begin
   MIn := TMemoryStream.Create;
   MOut := TMemoryStream.Create;
   Try
     MIn.LoadFromFile(InFile);
     MOut.SetSize(MIn.Size);
     if Encrypt then
       Result := MemoryEncrypt(MIn.Memory, MIn.Size, MOut.Memory, MOut.Size, Key)
     else
       Result := MemoryDecrypt(MIn.Memory, MIn.Size, MOut.Memory, MOut.Size, Key);
     MOut.SaveToFile(OutFile);
   finally
     MOut.Free;
     MIn.Free;
   end;
 end;

 function TextEncrypt(const s: string; Key: TWordTriple): string;
 begin
   Result := TextCrypt(s, Key, True);
 end;

 function TextDecrypt(const s: string; Key: TWordTriple): string;
 begin
   Result := TextCrypt(s, Key, False);
 end;

 function FileEncrypt(InFile, OutFile: String; Key: TWordTriple): boolean;
 begin
   Result := FileCrypt(InFile, OutFile, Key, True);
 end;

 function FileDecrypt(InFile, OutFile: String; Key: TWordTriple): boolean;
 begin
   Result := FileCrypt(InFile, OutFile, Key, False);
 end;