Re^4: Compressing and Encrypting files on Windows

, why don't you tell us what you really feel?

Because I thought it would get reaped ;-) The OPs post obviously annoyed me. I have no problem with people being wrong. Like most people I spout rubbish from time to time, but I typically have the good grace to add an AFAIK, IMHO, perhaps, maybe or whatever. It was the authoratative presentation of absolutely incorrect information that set me off.

cheers

tachyon

Comment on Re^4: Compressing and Encrypting files on Windows

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Re^5: Compressing and Encrypting files on Windows by MidLifeXis (Monsignor) on Nov 02, 2004 at 18:18 UTC
Just a point - if you compress and then encrypt, you are encrypting known pieces of data (block headers, dictionaries, etc). Depending on the compression algorithm, this may give a large enough chunk of data to assist an attack against the encrypted data stream. All of this is IIRC, of course ;) --MidLifeXis	[reply]
Re^6: Compressing and Encrypting files on Windows by tachyon (Chancellor) on Nov 02, 2004 at 23:21 UTC
As you say knowing that the first two bytes of a valid decrypt must be say the gzip header bytes 0x1f 0x8b does provide a small chink that can potentially be exploited. If you are that paranoid they are easy to hide. Making two passes with the encryption algorithm is one easy way. cheers tachyon	[reply]