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Re^5: Compressing and Encrypting files on Windows

by MidLifeXis (Monsignor)
on Nov 02, 2004 at 18:18 UTC ( [id://404700] : note . print w/replies, xml ) Need Help??


in reply to Re^4: Compressing and Encrypting files on Windows
in thread Compressing and Encrypting files on Windows

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

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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