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;