Note: This page is horribly out of
date.
You can find the current pages for the dm-crypt
project (the Linux kernel part) here:
https://gitlab.com/cryptsetup/cryptsetup/wikis/DMCrypt
and the project page for the command line tool
cryptsetup (with Linux Unified Key
Setup - LUKS) here: https://gitlab.com/cryptsetup/cryptsetup.
Old page:
Device-mapper is a new infrastructure in the Linux 2.6 kernel that provides
a generic way to create virtual layers of block devices that can do different
things on top of real block devices like striping, concatenation, mirroring,
snapshotting, etc... The device-mapper is used by the
LVM2 and
EVMS 2.x tools.
dm-crypt is such a device-mapper target that provides transparent encryption of
block devices using the new Linux 2.6 cryptoapi. The user can basically specify
one of the symmetric ciphers, a key (of any allowed size), an iv generation mode
and then the user can create a new block device in /dev. Writes to this device
will be encrypted and reads decrypted. You can mount your filesystem on it as usual.
But without the key you can't access your data.
It does basically the same as cryptoloop only that it's a much cleaner code and
better suits the need of a block device and has a more flexible configuration
interface. The on-disk format is also compatible. In the future you will be able
to specify other iv generation modes for enhanced security (you'll have to
reencrypt your filesystem though).
I've set up a Wiki.
There's a mailing list at .
If you want to subscribe, use the mailman
web interface or its
archive.
Gmane provides a NNTP interface and also a
web archive
for this mailing list.
There is support for dm-crypt in the latest official kernel
2.6.4
which you can find on kernel.org.
Please use the mirrors for downloads.
There is a HIGHMEM cryptoapi bug in kernels before 2.6.4-rc2, please
upgrade if you were using such a kernel.
The latest version of the native userspace setup tool is cryptsetup 0.1.
Clemens Fruhwirth is maintaining an
enhanced
version of cryptsetup with the LUKS extension that allows you to have an
on-disk block of metadata which is superior to the current mechanism and was
my long term plan anyway but I didn't find the time to implement that yet...
In the real world, trash is gone when you empty it. In Google Drive, the trash holds files for 30 days. Fine. But if you share a folder with someone, and they delete a file, it goes to their trash, not yours. You won’t know a critical file is missing until you search for it. And if you run out of storage? Google doesn't delete the oldest file; it stops you from receiving emails in Gmail. Because, of course, your email storage is tied to your drive storage. That brings me to...
We have all sent a link to a coworker or client, only to receive an immediate email stating they need to "Request Access." Google’s permissions framework is incredibly strict by default. If you log into multiple Google accounts on one browser, Drive often tries to open links using your primary account rather than the specific account the link was shared with, creating a loop of access denials. 7. Enforced File Conversion on Uploads
The Google Drive for Desktop app promises a seamless bridge between your local hard drive and the cloud. In reality, it is a notorious resource hog. It frequently spikes CPU usage, drains laptop batteries, and gets stuck in infinite loops trying to sync hidden system files. When a sync conflict occurs, rather than offering an elegant fix, it often duplicates files or hides them away in a cryptic cache folder. 4. Searching for Files is Shockingly Difficult
Your 15GB of free Google storage is not just for Drive. It is aggressively shared across Google Drive, Gmail, and Google Photos. google drive 10 things i hate about you
: Once purchased, you can watch it on any device with the Google TV app, including Android phones, iPhones, tablets, and smart TVs. Google Play Public Google Drive Links
If you edit a document offline, Drive often struggles to merge your changes once you reconnect, resulting in messy duplicate copies.
The Google Drive desktop application (formerly Backup and Sync, now Google Drive for Desktop) remains notoriously fickle. It frequently pauses syncing without warning, throws cryptic error messages, and occasionally creates duplicate "conflicting copies" of files when two devices sync at slightly different times. For power users who rely on local file management, the desktop app often feels more like a system resource hog than a seamless bridge to the cloud. 4. Search That Fails at Basic Organization In the real world, trash is gone when you empty it
The promise: "Enable offline access to work on the plane!" The reality: Chrome uses 6GB of RAM to keep a cached version of a 2MB document. And even after you toggle "Offline" mode, Drive will often refuse to open a file unless you were psychic enough to open it while online five minutes before you lost Wi-Fi. I have stared at the spinning "Waiting for network" circle in an airport more times than I have blinked.
You finally decide to leave? You want to migrate to Dropbox or OneDrive? You run Google Takeout. It takes 12 hours to prepare the archive. It then splits your data into 50 separate ZIP files of 2GB each. It names them takeout-archive-1.zip , takeout-archive-2.zip ... but good luck figuring out which ZIP has the file you need. Also, the folder hierarchy collapses. Comments disappear. Version history vanishes. Google Drive holds your data hostage behind a wall of ZIP files.
Despite these ten glaring flaws, Google Drive remains an essential tool for modern digital life. Its collaboration features are still unmatched, and it is too deeply integrated into our daily routines to abandon completely. But if you share a folder with someone,
This public link is valid for 7 days and shares a thread, including any personal information you added. This link or copies made by others cannot be deleted. If you share with third parties, their policies apply. Can’t copy the link right now. Try again later.
Files are “available” — just a token.
: Go to Drive Settings (the gear icon) and uncheck "Convert uploads to Google Docs editor format." This keeps your Office files in their native format while storing them. 7. Storage Sharing Across Services
Google reserves the right to scan your files for policy violations. While this is technically for safety, the lack of native end-to-end encryption means Google (and potentially others) can theoretically see what you're storing if they really want to. 10. The "New Folder" Hide-and-Seek
The on-disk layouts used by the current 2.6 cryptoloop are supported by dm-crypt.
Cryptoloop also uses cryptoapi so the name of the ciphers are the same. Cryptoloop also
supports ECB and CBC mode. Use <cipher>-ecb and
<cipher>-plain accordingly with dm-crypt. If you didn't
explicitly specify either -ecb or -cbc before you don't need it now, the default plain
IV generation will be used. There will be additional (incompatible, but more secure) possibilites
in the future because the unhashed sector number as IV is too predictible.
You'll need to figure out how your passphrase was turned into a key to use for losetup.
There are several patches floating around doing things differently. But usually cryptsetup
will provide a working solution to recreate the same key from your passphrase.
If you want to migrate from 2.4 cryptoloop please take a look at Clemens Fruhwirth's
Cryptoloop
Migration Guide. He describes the differences between 2.4 and 2.6 cryptoapi (or basically
the bugs in 2.4 cryptoapi...). If you need to cut the key size you can use the -s
option instead of playing with dd.
(BTW: Clemens has a i586 optimized version of the aes and serpent cipher on his page,
about twice as fast as the kernel implementation.)
Why dm-crypt?
Originally it started as a fun project because I wanted to play with the new Linux 2.6 internals.
I got a lot of great help from the device-mapper guys at Sistina (now Redhat). Thank you very
much!
It turned out that this implementation worked great and is very clean compared to the hacked
loop device. The device-mapper core provides much better facilities to stack block devices.
dm-crypt uses mempools to assure we never run into out-of-memory deadlocks when allocating
buffers.
Also the device-mapper configuration interface provides much more flexibility than the losetup
ioctl. And you can create as many devices as you want with any names you want and combine them
with other dm targets. Online device resizing is also possible, e.g. if you use dm-crypt on top
of a logical volume. There might perhaps even be LVM or EVMS support for device encryption
in the future.
But I don't want to use LVM!
You don't need LVM. Device-mapper is an all-purpose kernel feature,
not tied to LVM in any way.
What if I want to encrypt a filesystem and keep it in a file?
You can use dm-crypt on top of a normal loop device, call losetup and cryptsetup.
I'm going to add loop support to cryptsetup so it can do this for you.
I created my filesystem on the encrypted device. How can I keep it across reboots?
Very simple. Call cryptsetup again and supply the same passphrase. It only creates
a mapping, not a filesystem.
What if I want to change my passphrase?
At the moment you'll need to reencrypt your device because the passphrase is directly
tied to the key.
There are plans to write a tool that stores the master key on disk
and encrypted so it can be unlocked using a passphrase. You can then
change your passphrase on a regular basis.
If you want to reencrypt your filesystem you'll have to recreate a new one and move your files.
(I've got an experimantal tool in the works that allows you to reencrypt your block device on the fly,
assuming you don't reboot your machine...)
I've read about security problems.
Yes, the IV schemes currently supported by dm-crypt are the same as the ones supported by
cryptloop. There's the ECB mode which is a catastrophe (no IV at all) and the "plain"
mode, which is already a lot better. Older cryptoloops used ECB by default, but with dm-crypt
the default is "plain" (which is the unhashes sector number used as IV).
Since dm-crypt is extensible there will be better possibilities in the future, but they will be
on-disk incompatible with cryptoloop so you'll have to reencrypt.
Help! I can't figure out how to use my old encrypted data! I was using...
There are different implementations out there. Some are non-cryptoapi and/or
broken implementations. SuSE uses its own loop-twofish implementation which
makes dangerous assumptions and is broken when changing the blocksize
("timebomb crypto"). You cannot use this with dm-crypt.
Can I reencrypt my data without copying all the files?
There's an experimental and unfinished dmconvert program
that can reencrypt the data while the filesystem is mounted. If you can get it running it should
be safe enough to not eat your data, but make sure you don't interrupt it or crash your system
while it is running. Don't blame me if something goes wrong.
Can I use encrypted swap?
Yes. You can specify a key file /dev/random and run mkswap afterwards, so the device will be
created with a different key each time and the data is not accessible at all after a reboot.
Is there a mailing list?
I've set up a Wiki.
There's a mailing list at .
If you want to subscribe, use the mailman
web interface or its
archive.
Gmane provides a NNTP interface and also a
web archive
for this mailing list.
My system hangs for some time in regular intervals when writing to encrypted disks.
You are probably using Linux 2.6.4. Du to the introduction of kthread pdflush is running at nice level -10,
which means that the kernels treats dm-crypt writes as a real time task and doesn't allow scheduling.
Solution: Switch to 2.6.5 or later or renice pdflush manually.
Can I use the mount command itself to do all the magic needed?
I've written an experimental patch for this, see
my post
in the mailing list archive.
Where can I send my contributions?
Because maintaining a web page takes time and people keep mailing me a lot of
things I could integrate they can enter it into this nice Wiki.
Please contact the mailing list: dm-crypt@saout.de. Or in case there is a problem with the mailing list, me: .