[yunqa.de] Re: DIZipWriter: streaming question
- From: Delphi Inspiration <delphi@xxxxxxxx>
- To: yunqa@xxxxxxxxxxxxx
- Date: Tue, 09 Dec 2008 16:27:27 +0100
Yeoh Ray Mond wrote:
>Given what I've seen re the requirement to pass the CRC32 of the 'file' to the
>zip writer before compressing and encrypting a 'file', I would guess that it's
>impossible to also encrypt a stream that's passed block my block, as happens
>in my case.
Only if you use the PK ZIP 2.0 encryption. This encryption algorithm uses the
CRC32 value of all data for its initialization.
With WinZip AES encryption (TDIZipWriter.EncryptionMethod = emWinZipAes128),
you can write your archive block by block just as you would do without
encryption.
Attached is a simple project to demonstrate how this works.
>Is that true? Does that requirement also apply to encrypting streams in the
>zip64 format?
I did not look into the Zip64 format, but given that the CRC32 restriction does
not apply to WinZip AES encryption in standard format I expect no different for
Zip64.
Ralf
//------------------------------------------------------------------------------
program DIZipWriter_EncryptMultiple_AES;
{$I DI.inc}
{$APPTYPE Console}
uses
{$IFDEF FastMM}FastMM4, {$ENDIF}SysUtils, DIZipWriter;
var
FileName: string = '';
s1: AnsiString = '';
s2: AnsiString = '';
ZipWriter: TDIZipWriter;
begin
FileName := ExtractFilePath(ParamStr(0)) + 'test_aes.zip';
s1 := 'This is a first string';
s2 := ' which is followed by a 2nd string.';
ZipWriter := TDIZipWriter.Create{$IFNDEF
DI_No_ZipWriter_Component}(nil){$ENDIF};
// Enabl WinZip AES encryption and set the password.
ZipWriter.EncryptionMethod := emWinZipAes128;
ZipWriter.Password := 'password';
// Create a new Zip file in the temp folder.
ZipWriter.NewZipFile(FileName);
// Pass the Crc32 value to the new Zip entry.
ZipWriter.AddEntry('TwoStrings.txt');
// Write the two AnsiStrings, one at a time.
ZipWriter.WriteStrA(s1);
ZipWriter.WriteStrA(s2);
// Close the Zip entry, finish the Zip archive and close the file on disk.
ZipWriter.Free;
end. program DIZipWriter_EncryptMultiple_AES;
{$I DI.inc}
{$APPTYPE Console}
uses
{$IFDEF FastMM}FastMM4, {$ENDIF}SysUtils, DIZipWriter;
var
FileName: string = '';
s1: AnsiString = '';
s2: AnsiString = '';
ZipWriter: TDIZipWriter;
begin
FileName := ExtractFilePath(ParamStr(0)) + 'test_aes.zip';
s1 := 'This is a first string';
s2 := ' which is followed by a 2nd string.';
ZipWriter := TDIZipWriter.Create{$IFNDEF
DI_No_ZipWriter_Component}(nil){$ENDIF};
// Enabl WinZip AES encryption and set the password.
ZipWriter.EncryptionMethod := emWinZipAes128;
ZipWriter.Password := 'password';
// Create a new Zip file in the temp folder.
ZipWriter.NewZipFile(FileName);
// Pass the Crc32 value to the new Zip entry.
ZipWriter.AddEntry('TwoStrings.txt');
// Write the two AnsiStrings, one at a time.
ZipWriter.WriteStrA(s1);
ZipWriter.WriteStrA(s2);
// Close the Zip entry, finish the Zip archive and close the file on disk.
ZipWriter.Free;
end.
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