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From Chris Bamford <>
Subject compress - 3 questions about encryption
Date Fri, 17 Sep 2010 11:45:51 GMT

I hope someone can advise me.
I am developing Java code to handle archives using commons compress and am currently focusing
on ZIP files.  I understand that ZIPs can be encrypted in two ways:

   (a) the contained entries can be plain text or encrypted
   (b) the whole ZIP itself can be encrypted

QUESTION 1:  Is this correct?  
If so, I need to be able to detect both.  So far I only know how to handle (a), by using this

    public boolean checkZipEntryIsEncrypted(ZipArchiveEntry entry) {
        boolean encrypted = false;

        // Check if zip file is encrypted
        if (zfile != null) {
            if (! zfile.canReadEntryData(entry)) {
                encrypted = true;

        return encrypted;

QUESTION 2: is this the right way to detect encrypted entries?

QUESTION 3: what is the right way to detect that the ZIP itself is encrypted?


- Chris

Chris Bamford

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