Berkeley CSUA MOTD:Entry 28837
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2025/07/10 [General] UID:1000 Activity:popular
7/10    

2003/6/25-26 [Computer/SW/Security] UID:28837 Activity:high
6/25    Does anyone have any day-to-day experience with encrypting
        many (O(100s of MBs)) of files on their hard drives?  For
        instance, if you have a laptop with all of your electronic
        bank statements/etc on it, and wanted to encrypt these with
        a key that you have on a compact flash or something similar?
        I know it is doable, but I'm wondering if it is in a way that
        is still usable?
        \_ why not use an encrypting file system...
                \_ MS EFS has somehighly annoying problems, like making it
                   really easy to accidentally generate new keys (which are
                   not backed up easily.)  Look at CFS under FreeBSD.  -John
           \_ The critical point would still be key management, right?
              You don't want to have the key on the machine if it
              gets stolen, but you still want fairly normal access to
              the files...  Put it on a "secret" web page so that you
              can download it to use?  Or on compact flash?  Does
              anyone do this kind of thing?
           \_ but that would be cheating.
           \_ is there any free/open source encrypted file system?
              \_ pffft.  You might as well just format the drive now.
           \_ Abe's Linux Encrypted Filesystem howto:
              http://www.abeowitz.com/crypto
              Also I've seen similar stuff with windows that uses a
              vxd to add encrypted filesystem support and mounts an
              encrypted block file.
              \_ no relation. -abe
        \_ Just tell your g/f that you look at porn. Stop trying to hide
           it from her.
ERROR, url_link recursive (eces.Colorado.EDU/secure/mindterm2) 2025/07/10 [General] UID:1000 Activity:popular
7/10    

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2013/6/6-7/31 [Politics/Foreign/Asia/China, Computer/SW/Security] UID:54690 Activity:nil
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2012/8/26-11/7 [Computer/SW/Security] UID:54465 Activity:nil
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2012/8/29-11/7 [Computer/SW/Security] UID:54467 Activity:nil
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2012/8/7-10/17 [Computer/SW/Security] UID:54455 Activity:nil
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2011/4/27-7/30 [Computer/SW/Security, Computer/SW/Unix] UID:54096 Activity:nil
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2011/5/19-7/30 [Computer/SW/Security] UID:54110 Activity:nil
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        \_ person k
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2011/2/14-4/20 [Computer/SW/Unix] UID:54039 Activity:nil
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Cache (2481 bytes)
www.abeowitz.com/crypto -> www.abeowitz.com/crypto/
Last Update: 2/20/2003 What is an Encrypted File System? It is mathematically difficult to decrypt the data in this form, and therefore useless to most people without a password and knowledge of the encryption algorithm. This allows the media storage structure and file names to be seen, while hiding the contents within each file. Each file may be encrypted with a different password and/or algorithm. Given sufficient computing power, I believe all algorithms are crackable. The difference is in the amount of computing power and time the cracker has available to him. In most cases, your data is safe from the average computer geek. In other words, file system encryption is only effective when your data is not mounted. Losetup /sbin/losetup /dev/loop0 test -e blowfish Available keysizes (bits): 128 160 192 256 Keysize: 256 Password: OK, now you have your virtual device. All your data will go through the loop0 device, get encrypted and stored within the file. Formatting Next we need to place a filesystem on that loop device. Note 2: Use '-b 2048' if you plan to make a CDROM image. Follow the directions for the test above EXCEPT when you make the file system, use a '-b 2048'. Note: Do NOT use EXT3, you don't need a journal for read only file systems, it will only take up space. For example: mke2fs /dev/loop0 -b 2048 The block size of 2048 is necessary since the CDROM block size is 2048. Otherwise, you will see a file directory, but the file data will be offset and thus corrupted. Burn the CD Nothing special here: cdrecord dev=0,0,0 speed=12 -v test Using the CD 1. Note: It is best to experiment with a CDRW and a SMALL file first. Encrypt a Block Device or Partition You can encrypt almost any block storage device, including Zip drives, floppy disks and whole hard drives or individual partitons. Note: dd from urandom to the device before you connect it to a loop device. Modifying your /etc/fstab One of my encrypted file system lines looks like this: /dev/hdd /mnt/ezip ext3 encryption=blowfish,user,noauto,rw,loop 0 0 Note that I can add this line for non encrypted zip disks: /dev/hdd /mnt/zip ext3 user,noauto,rw,loop 0 0 When I type 'mount /mnt/zip', I mount the non-encrypted zip disk. Note that with the encrypted devices in your fstab file, you no longer need to use losetup! If EXT2FS formats based on the geometry of the disk, couldn't this information be used to brute force attack the encryption based on the file size and location of the inodes?