Suggest best encryption type when adding file(s) to .zip

[miskox]

I have a password protected .zip file. Protection is "zip 2.0". I usually pack items with AES256 (so this option is preselected). So when I wanted to add a file to the existing .zip (with zip2.0 password) new file was added with AES256 encryption (because this encryption was pre-selected). When I tried to unzip the files (with unzip.exe) I received the following error:

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unzip.exe -t -P password zipfile.zip
skipping: filename.txt                unsupported compression method 99
 testing: anotherfile.txt             OK

(other files were checked ok)

I would suggest that TC would check the .zip and maybe display a message and/or select other type of encryption method if required.

Thanks.
Saso

[Hacker]

Moderator message from: Hacker

Moved seven off-topic posts to ENG: Small talk / Geplauder / Forum Moderation / Spam-Report / Off-Topic and edited initial post for clarity.

[petermad]

Support - if feasible. The problem is that TC has to examine all files inside the existing acrchive until it finds an encrypted file, it could perhaps slow down things too much. On the other hand, TC shows the e-attribute for encrypted files in the file list, so it might not be so bad to check the encryption method of the first found file with the e-attribute set, and warn if that is not the same encryption method as the currently chosen method, so the user can change the method, if he does not want mixed encryption methods in the zip file.

[Usher]

2miskox
Could you describe your expectations in more details? I don't understand how it should work so I describe what is available now.

1. You can pack/unpack zip files using TC without any external tools. TC has no problem with zip20crypt (a.k.a. zip 2.0 encryption).

If you want to know more info about archived files, you can TEST archive in TC with Alt+Shift+F9. In case of any problems reported by TC during test, you can write down the problematic filename, then you can enter zip archive in TC, browse it like a directory and navigate to find needed file. Than you can press Alt+Enter on a found file to see info about compression/encryption methods used.

Unfortunately, you cannot add custom columns to see that info when browsing archive like a directory in TC. Such a feature is available in 7zfm (7-zip File Manager), when you turn on needed columns in view there. If the custom columns work in TC for archives, you could probably use similar custom columns provided by Total7zip plugin. Note that TC provides also 7zip library so the info provided in custom columns may be available without plugins for both zip and 7zip formats.

2. If you want to use external tools, you should know their features. TC isn't aware of such features and can only do whatever you configure personally.

Unzip isn't a good choice. It hasn't been updated for a long time. There were only security patches in last ten years, but I can't find such binaries compiled for Windows. That's why I suspect that your unzip is a buggy and outdated tool, which probably doesn't support Unicode and newest encryption/compression methods.
Zip format also isn't a good choice. You can find many reports about problems with encoding of filenames in zip archives - in this forum and in the Internet. Some tools have problems with creating zip files larger than 2 GiB - they either don't support deflate64 compression method or don't save proper metadata in zip file.

That's why many people stopped using pkzip/pkunzip/zip/unzip tools and zip format long time ago - they use 7-zip instead. It's not only 7zfm, there are also command line tools which also support zip archives. For example you can use the following command to get detailed archive info:

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7z.exe l -slt zipfile.zip

As you can see, there is no problem to list needed info fast enough in most cases. However, it may take a few minutes to get such info for huge archives with millions of files (try to open *.esd or *.wim archives from MS Windows 10/11 installers), so there may be some size limit needed in TC.