October 25

Linux: auto mount cryptsetup/LUKS/encrypted loop device

apt-get install cryptsetup

Using dm-crypt/LUKS/cryptsetup by doing the following steps:

1. Create a sparse disk image file: dd if=/dev/zero of=IMAGEFILE bs=1 count=1 seek=SIZE
2. Generate a random key in a file: dd if=/dev/random of=KEYFILE bs=1024 count=1
3. Use cryptsetup luksFormat –key-file KEYFILE –cipher aes-xts-plain –size 512 IMAGEFILE (Or use another cipher and key length. Note that 512 here will give you AES with 256 bits because of XTS.) Example 2: cryptsetup luksFormat –key-file KEYFILE –cipher aes-xts-plain64:sha512 -s 512 IMAGEFILE
4. Open crypt container: cryptsetup luksOpen –key-file KEYFILE IMAGEFILE NAME
5. Create file system on /dev/mapper/NAME.
6. Mount file system as usual.

Your script would just have to do steps 4 and 6. For unmounting/closing, umount the file system and call cryptsetup luksClose NAME.

Note that using sparse files will leak the information which sectors of the disk have been used already (the same way as not overwriting a partition with random data before encrypting it). It is up to you to decide whether this is ok for you.

Also note that deleting files will not make the disk image smaller. The sparse file will grow monotonically.

By: P Wendler

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Posted October 25, 2014 by Timothy Conrad in category "Linux

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If I were to describe myself with one word it would be, creative. I am interested in almost everything which keeps me rather busy. Here you will find some of my technical musings. PGP: 4CB8 91EB 0C0A A530 3BE9 6D76 B076 96F1 6135 0A1B