question about zip

[gnupg+Steven.Murdoch@cl.cam.ac.uk]

> - is it possible to define maximal file size when ciphering/zipping a file?

Not as far as I know.
 
> I need to cipher and zip +-20GB file and I need the final file to be
> separated to more files that I can burn onto CDs (the compression rating
> should better then 80%).
> 
> Is it possible in one step? Or do I need to cipher the file with no
> compression, and then use for example rar to pack it?

If you encrypted the file using no compression then RAR will not be able to 
compress it very well (in general encrypted data compresses very poorly).

Also encrypting content that is uncompressed *may* decrease security by a 
small amount, however there is some discussion as to whether the converse is 
true.

You would be better encrypting the data with compression turned on then using 
RAR/Zip etc... to split the file into smaller chunks. This splitting step will 
not reduce the size significantly but it will split up the data. For the 
second splitting step you could even turn off compression in the program you 
are using to save time.

Another option is compressing the file before encrypting it, this may or may 
not make your file smaller - it depends on the nature of the original file.

> Also - I hope there is no limit related to the file size (is it possible to
> cipher/zip so big files I hope).

Sorry, I don't know.
 
Steven Murdoch.