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Re^2: Compressing and Encrypting files on Windows

by Elgon (Curate)
on Nov 01, 2004 at 15:28 UTC ( #404324=note: print w/ replies, xml ) Need Help??


in reply to Re: Compressing and Encrypting files on Windows
in thread Compressing and Encrypting files on Windows

Tachyon is precisely correct.

When you encrypt something, the output is highly entropic and there will be no redundancy in the text. Compression works by removing redundancy from the file, so, given that there is no redundancy in an encrypted file there will be no compression.

See... this, for example. Pay particular reference to the section which states "Compression after encryption is silly. If an encryption algorithm is good, it will produce output which is statistically indistinguishable from random numbers and no compression algorithm will considerably compress random numbers. On the other hand, if a compression algorithm succeeds in finding a pattern to compress out of an encryption's output, then a flaw in that algorithm has been found. In the majority of encryption utilities (e.g., PGP ) the data is first compressed before it is actually encrypted."

It is better either to be silent, or to say things of more value than silence. Sooner throw a pearl at hazard than an idle or useless word; and do not say a little in many words, but a great deal in a few.

Pythagoras (582 BC - 507 BC)


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