* 1.5 Who wrote this?
- Current FAQ maintainer is Arno Wagner <arno@wagner.name>. Other
- contributors are listed at the end. If you want to contribute, send
- your article, including a descriptive headline, to the maintainer,
- or the dm-crypt mailing list with something like "FAQ ..." in the
- subject. You can also send more raw information and have me write
- the section. Please note that by contributing to this FAQ, you
- accept the license described below.
+ Current FAQ maintainer is Arno Wagner <arno@wagner.name>. If you
+ want to send me encrypted email, my current PGP key is DSA key
+ CB5D9718, fingerprint 12D6 C03B 1B30 33BB 13CF B774 E35C 5FA1 CB5D
+ 9718.
+
+ Other contributors are listed at the end. If you want to contribute,
+ send your article, including a descriptive headline, to the
+ maintainer, or the dm-crypt mailing list with something like "FAQ
+ ..." in the subject. You can also send more raw information and
+ have me write the section. Please note that by contributing to this
+ FAQ, you accept the license described below.
This work is under the "Attribution-Share Alike 3.0 Unported"
license, which means distribution is unlimited, you may create
Side-note: That has limited value against the authorities. In
civilized countries, they cannot force you to give up a crypto-key
- anyways. In the US, the UK and dictatorships around the world,
- they can force you to give up the keys (using imprisonment or worse
- to pressure you), and in the worst case, they only need a
- nebulous "suspicion" about the presence of encrypted data. My
- advice is to either be ready to give up the keys or to not have
+ anyways. In quite a few countries around the world, they can force
+ you to give up the keys (using imprisonment or worse to pressure
+ you, sometimes without due process), and in the worst case, they
+ only need a nebulous "suspicion" about the presence of encrypted
+ data. Sometimes this applies to everybody, sometimes only when you
+ are suspected of having "illicit data" (definition subject to
+ change) and sometimes specifically when crossing a border. Note
+ that this is going on in countries like the US and the UK, to
+ different degrees and sometimes with courts restricting what the
+ authorities can actually demand.
+
+ My advice is to either be ready to give up the keys or to not have
encrypted data when traveling to those countries, especially when
- crossing the borders.
+ crossing the borders. The latter also means not having any
+ high-entropy (random) data areas on your disk, unless you can
+ explain them and demonstrate that explanation. Hence doing a
+ zero-wipe of all free space, including unused space, may be a good
+ idea.
Disadvantages are that you do not have all the nice features that
the LUKS metadata offers, like multiple passphrases that can be
not work anymore. Therefore it is better to encrypt the RAID
device, e.g. /dev/dm0 .
+ This means that the typical layering looks like this:
+
+ Filesystem <- top
+ |
+ Encryption
+ |
+ RAID
+ |
+ Raw partitions
+ |
+ Raw disks <- bottom
+
+ The big advantage is that you can manage the RAID container just
+ like any RAID container, it does not care that what is in it is
+ encrypted.
+
* 2.7 How do I read a dm-crypt key from file?
own tool that in turn gets the key from the more secure key
storage.
+ For TPM support, you may want to have a look at tpm-luks at
+ https://github.com/shpedoikal/tpm-luks. Note that tpm-luks is not
+ related to the cryptsetup project.
+
* 2.13 Can I resize a dm-crypt or LUKS partition?
for that.
+ * 2.14 How do I Benchmark the Ciphers, Hashes and Modes?
+
+ Since version 1.60 cryptsetup supports the "benchmark" command.
+ Simply run as root:
+
+ cryptsetup benchmark
+
+ It will output first iterations/second for the key-derivation
+ function PBKDF2 parameterized with different hash-functions, and
+ then the raw encryption speed of ciphers with different modes and
+ key-sizes. You can get more than the default benchmarks, see the
+ man-page for the relevant parameters. Note that XTS mode takes two
+ keys, hence the listed key sizes are double that for other modes
+ and half of it is the cipher key, the other half is the XTS key.
+
+
+ * 2.15 How do I Verify I have an Authentic cryptsetup Source Package?
+
+ Current maintainer is Milan Broz and he signs the release packages
+ with his PGP key. The key he currently uses is the "RSA key ID
+ D93E98FC", fingerprint 2A29 1824 3FDE 4664 8D06 86F9 D9B0 577B
+ D93E 98FC. While I have every confidence this really is his key and
+ that he is who he claims to be, don't depend on it if your life is
+ at stake. For that matter, if your life is at stake, don't depend
+ on me being who I claim to be either.
+
+ That said, as cryptsetup is under good version control, a malicious
+ change should be noticed sooner or later, but it may take a while.
+ Also, the attacker model makes compromising the sources in a
+ non-obvious way pretty hard. Sure, you could put the master-key
+ somewhere on disk, but that is rather obvious as soon as somebody
+ looks as there would be data in an empty LUKS container in a place
+ it should not be. Doing this in a more nefarious way, for example
+ hiding the master-key in the salts, would need a look at the
+ sources to be discovered, but I think that somebody would find that
+ sooner or later as well.
+
+ That said, this discussion is really a lot more complicated and
+ longer as an FAQ can sustain. If in doubt, ask on the mailing list.
+
+
3. Common Problems
diagnosing and (if still possible) repairing this.
- * 4.2 Can a bad RAM module cause problems?
+ * 4.2 I cannot unlock my LUKS container! What could be the problem?
+
+ First, make sure you have a correct passphrase. Then make sure you
+ have the correct key-map and correct keyboard. And then make sure
+ you have the correct character set and encoding, see also
+ "PASSPHRASE CHARACTER SET" under Section 1.2.
+
+ If you are sure you are entering the passphrase right, there is the
+ possibility that the respective key-slot has been damaged. There
+ is no way to recover a damaged key-slot, except from a header
+ backup (see Section 6). For security reasons, there is also no
+ checksum in the key-slots that could tell you whether a key-slot has
+ been damaged. The only checksum present allows recognition of a
+ correct passphrase, but that only works if the passphrase is
+ correct and the respective key-slot is intact.
+
+ In order to find out whether a key-slot is damaged one has to look
+ for "non-random looking" data in it. There is a tool that
+ automatizes this in the cryptsetup distribution from version 1.6.0
+ onwards. It is located in misc/keyslot_checker/. Instructions how
+ to use and how to interpret results are in the README file. Note
+ that this tool requires a libcryptsetup from cryptsetup 1.6.0 or
+ later (which means libcryptsetup.so.4.5.0 or later). If the tool
+ complains about missing functions in libcryptsetup, you likely
+ have an earlier version from your distribution still installed. You
+ can either point the symbolic link(s) from libcryptsetup.so.4 to
+ the new version manually, or you can uninstall the distribution
+ version of cryptsetup and re-install that from cryptsetup >= 1.6.0
+ again to fix this.
+
+
+ * 4.3 Can a bad RAM module cause problems?
LUKS and dm-crypt can give the RAM quite a workout, especially when
combined with software RAID. In particular the combination RAID5 +
did a verify.
- * 4.3 How do I test RAM?
+ * 4.4 How do I test RAM?
First you should know that overclocking often makes memory
problems worse. So if you overclock (which I strongly recommend
foot, you can figure out how to do it yourself.
- * 5.19 What about SSDs or Flash Drives?
+ * 5.19 What about SSDs, Flash and Hybrid Drives?
The problem is that you cannot reliably erase parts of these
devices, mainly due to wear-leveling and possibly defect
done in some fashion so that larger writes do not cause a lot of
small internal updates.
- The thing is that the mappings between outside-adressable sectors
+ The thing is that the mappings between outside-addressable sectors
and inside sectors is arbitrary (and the vendors are not talking).
Also the discarded sectors are not necessarily erased immediately.
They may linger a long time.
If you trust the device vendor (you probably should not...) you can
try an ATA "secure erase" command for SSDs. That does not work for
- USB keys though. And if it finishes after a few seconds, it was
- possibly faked by the SSD.
+ USB keys though and may or may not be secure for a hybrid drive. If
+ it finishes on an SSD after a few seconds, it was possibly faked.
+ UNfortunately, for hybrid drives that indicator does not work, as
+ the drive may well take the time to dully erase the magnetic part,
+ but only mark the SSD/Flash part as erased while data is still in
+ there.
If you can do without password management and are fine with doing
- physical destruction for permenently deleting data (allways after
+ physical destruction for permanently deleting data (always after
one or several full overwrites!), you can use plain dm-crypt or
LUKS.
security as on a magnetic disk.
If you are concerned about your laptop being stolen, you are likely
- fine using LUKS on an SSD. An attacker would need to have access
- to an old passphrase (and the key-slot for this old passphrase
- would actually need to still be somewhere in the SSD) for your
- data to be at risk. So unless you pasted your old passphrase all
- over the Internet or the attacker has knowledge of it from some
- other source and does a targetted laptop theft to get at your
- data, you should be fine.
+ fine using LUKS on an SSD or hybrid drive. An attacker would need
+ to have access to an old passphrase (and the key-slot for this old
+ passphrase would actually need to still be somewhere in the SSD)
+ for your data to be at risk. So unless you pasted your old
+ passphrase all over the Internet or the attacker has knowledge of
+ it from some other source and does a targeted laptop theft to get
+ at your data, you should be fine.
6. Backup and Data Recovery
projects / platform / upstream / cryptsetup.git / blobdiff