Gentoo Archives: gentoo-security

From: Randy Barlow <randy@×××××××××××××××××.com>
To: gentoo-security@l.g.o
Subject: Re: [gentoo-security] Encrypting a user home folder on a laptop
Date: Sat, 16 Feb 2008 00:08:39
Message-Id: 47B62960.8050902@electronsweatshop.com
In Reply to: Re: [gentoo-security] Encrypting a user home folder on a laptop by bmicek@speakeasy.net
bmicek@×××××××××.net wrote:
> I spent time about a year ago looking into good encryption. At that > time, cryptsetup was the best bet. Its really easy to use. With > cryptsetup, your best off encrypting an entire filesystem/partition so > there are no restrictions regarding size. > > As far as ciphers, there are three popular ones that are 256 bits in the > Linux kernel. You'll have to pick the one(s) you like best. Generally, > everyone agrees Serpent is the strongest, followed by AES then followed > by TwoFish. From my tests, performance of the algorithms is in reverse > order (meaning TwoFish is the fastest). Linux is a bit behind last I > checked regarding encription modes of operation and seems to only offer > ECB or CBC. CBC is Chain Block Cipher and is based on an IV which is > like an index into your media. The IV is used to encript a block of > data so a previous identical block wont be identically encrypted. As > far as your question regarding one-bit changes, a one bit change will > have the effect you mentioned but only for one encrypted block. > > I'd recommend reading up on the ciphers to see what you like. There has > been some talk about TwoFish being broken however I find it hard to > believe. There has been a lot of talk about TrueCrypt on Linux. From > what I can tell, it seems a bit more advanced and supports different > (more modern?) modes of encryption.
Thanks for the reply Brian! In a course I am taking this semester, we have learned the nitty gritty of AES, and I think I am pretty happy with that one given a long enough key (256 is way plenty!) I have been playing around with the creation of the file for the loopback block device for dm-crypt, and I have learned some surprising things about filesystems. Can anybody explain the following to me? If I create a file like this: dd if=/dev/zero bs=1000000000 of=/path/to/crytped/file it makes a file that takes up 1 GB of hard drive space. It takes a while to write to disk, and you will notice that the file is 1 GB with ls -l and you will also notice a change in the space for the partition using df. If I create a file like this: dd bs=1 seek=1GB if=/dev/null of=/path/to/crypted/file it makes a file that reports itself to be 1 GB long by ls -l, but doesn't seem to write 1 GB to the disk. Also, df doesn't report 1 GB less than before you run the command. What's happening here? I had assumed before I did this that the output of ls -l is the actual number of bits consumed by a file, but that doesn't seem to be the case anymore. I created a file using the second command, and now as I copy files into it I can see the disk space going down bit by bit. This is really what I wanted in the first place, but I am just confused as to what is really going on. Could anybody explain, please? -- Randy Barlow http://electronsweatshop.com -- gentoo-security@l.g.o mailing list

Replies

Subject Author
Re: [gentoo-security] Encrypting a user home folder on a laptop Christian Spoo <mail@××××××××××××××.info>
Re: [gentoo-security] Encrypting a user home folder on a laptop William Kenworthy <billk@×××××××××.au>
Re: [gentoo-security] Encrypting a user home folder on a laptop Samuel Halicke <tuscantwelve@×××××.com>