(Though I suppose a streaming decompressor could decompress to a temporary location and then only move non-deleted entries into their final place.) it can be overwritten by new data, and then re-appended.) I think this approach allows tools to also "delete" data by simply removing the entry from the central directory, and re-appending it w/o, so the central directory is essentially the authoritative source for the ZIPs contents. It would still be huge, given the other tricks in the article.)Īlso, I think you can "append" to ZIPs (this is why the central directory is at the end, s.t. (In the streaming case, I think you'd see exactly 1 file. If you're streaming, you're using the local file headers, but for ZIPs such as those in the article, you will see many less LHFs than had you looked them up in the central directory, b/c they overlap. But this is only apparent if you're using the central directory, which you can't if you're streaming, since it appears after all the data. The core idea of the article is overlapping the various files within the ZIP, s.t. But the types of ZIPs in the article are going to act differently if you tried streaming them. For a normal, created in one-shot ZIP, yes. From what I could see, there were no false positives for rejecting gaps between referenced local files on a small sample of 5000 archives. The goal of is to scan email attachments at the gateway and reject zip archives that might prove dangerous to more vulnerable zip software running downstream (MS Office, macOS) etc.Īlso, as you say, I don't think incrementally updated archives are used much. Of course, the spec advocates parsing backwards according to the central directory record, but implementations exist that don't do this. These "invisible" dead zones can be used for malware stuffing, or to exploit ambiguity across different zip implementations, those that parse forwards (using the local file header as the canonical header) and those that parse backwards (using the central directory header as the canonical header).įor example, a malware author might put an EXE in the first version of a file, and a TXT in the second version of that same file. For a rarely used feature, it's a dangerous feature. It was a feature back in the day, but as you say it also leaves dead zones in the archive. And since it's free to try for an extended period, there's no reason not to check it out to see if it will work for you.Įditors' note: This is a review of the trial version of WinZip Mac 3.Yes, I made a decision to reject incrementally updated archives. It's not packed with features, but the features it does have are exactly the ones you're looking for in an app of this type. WinZip delivers exactly what it promises. Not free: While you can use WinZip for free during the 45-day trial period, you will eventually have to purchase a license for $29.95 if you want to continue using it indefinitely. This is a handy addition, and a nice way to safeguard important documents and sensitive communications. Password protection: If you opt to ZIP and email all at once, you can also choose the Encrypt option and include password protection on one or all of your files. The archive is zipped automatically, and a little bar graph at the top shows you how much space the files take up zipped versus unzipped. The main screen lays out your options clearly, and to add files to an archive, you can just drag and drop them in. Through its intuitive interface, WinZip makes these features accessible to users of all skill levels, and it runs quickly and smoothly.Įxcellent interface: Even if you've never used a program like this before, you'll have no problem finding your way around in WinZip. WinZip gives you the ability to compress any group of files quickly, and then burn them to a disk or email them directly from the app.
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