Re: building compatible zip files "by hand" that are encrypted and compressed

Greg,

Thank you, that is very helpful information.

Supposing then I accept the vulnerable but universal
96-bit encryption, how formidable do you think my two
tasks are:  1) Encrypting and compressing the files on
the "upstream" side, before the client sends them, and
2) Building the ZIP file from the (already compressed
and encrypted) files later?

I can see already that if I compress the file on the
client before sending it to the server I must also
transmit the original file size to the server; and if
I eventually allow the end user to select from a menu
of encryption methods I must also transmit which
algorithm was used.  I can add those items to my
protocol very easily.  I'm wondering what else I might
need to send to the server so that it can construct a
valid ZIP file later.

Are there any librarys or classes related to info-zip
that would make the two tasks easier?

Any pointers to documentation would be welcome too.

Thanks again, Greg.

ed

--- Greg Roelofs <[email protected]> wrote:
> Ed Fair <ed_fair-/[email protected]> wrote:
> 
> > I must ensure, during client preprocessing, that
> files
> > are compressed and encrypted in a manner
> compatible
> > with the common UNZIP utilities.
> 
> That rules out AES.  Only the newest WinZip or PKZIP
> supports it--
> the two are not compatible with each other, and I
> think the other
> one uses a different strong-crypto algorithm. 
> Info-ZIP supports
> only the old-style 96-bit,
> known-plaintext-susceptible variant that
> everybody supports.  So either use that or forget
> about portability.
> 
> Greg
> _______________________________________________
> Info-ZIP mailing list
> [email protected]
> http://lists.wku.edu/mailman/listinfo/info-zip


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