From: Arno Wagner Date: Sat, 4 Dec 2010 02:41:33 +0000 (+0000) Subject: fixes to formatting X-Git-Tag: upstream/1.6~546 X-Git-Url: http://review.tizen.org/git/?p=platform%2Fupstream%2Fcryptsetup.git;a=commitdiff_plain;h=80c101d15ca8e51354247c5ad371675b6b695fbd fixes to formatting git-svn-id: https://cryptsetup.googlecode.com/svn/trunk@396 36d66b0a-2a48-0410-832c-cd162a569da5 --- diff --git a/FAQ b/FAQ index 0634d2a..d137944 100644 --- a/FAQ +++ b/FAQ @@ -1,17 +1,9 @@ Sections + 1. General Questions2. Setup3. Common Problems4. Troubleshooting5. + Security Aspects6. Backup and Data Recovery7. Issues with Specific + Versions of cryptsetupA. Contributors -1. General Questions -2. Setup -3. Common Problems -4. Troubleshooting -5. Security Aspects -6. Backup and Data Recovery -7. Issues with Specific Versions of cryptsetup -A. Contributors - - -1. General Questions - + 1. General Questions * What is this? @@ -31,7 +23,6 @@ A. Contributors limitations imposed by the LUKS security model BEFORE you face such a disaster! - * Who wrote this? Current FAQ maintainer is Arno Wagner . Other @@ -53,14 +44,12 @@ A. Contributors this license is best suited for the purpose at hand and creates the least problems. - * Where is the project website? There is the project website at http://code.google.com/p/cryptsetup/ Please do not post questions there, nobody will read them. Use the mailing-list instead. - * Is there a mailing-list? Instructions on how to subscribe to the mailing-list are at on the @@ -77,9 +66,7 @@ A. Contributors with just the word "help" in the subject or message body. Make sure to send it from your list address. - -2. Setup - + 2. Setup * Can I encrypt an already existing, non-empty partition to use LUKS? @@ -95,7 +82,6 @@ A. Contributors For backup, plain GNU tar works well and backs up anything likely to be in a filesystem. - * How do I use LUKS with a loop-device? Just the same as with any block device. If you want, for example, @@ -108,7 +94,6 @@ A. Contributors Afterwards just use /dev/loop0 as a you would use a LUKS partition. To unmap the file when done, use "losetup -d /dev/loop0". - * When I add a new key-slot to LUKS, it asks for a passphrase but then complains about there not being a key-slot with that passphrase? @@ -120,7 +105,6 @@ A. Contributors the already configured key-slots in order to be able to configure a new key-slot. - * How do I read a dm-crypt key from file? Note that the file will still be hashed first, just like keyboard @@ -128,7 +112,6 @@ A. Contributors cryptsetup create --key-file keyfile e1 /dev/loop0 - * How do I read a LUKS slot key from file? What you really do here is to read a passphrase from file, just as @@ -154,7 +137,6 @@ A. Contributors cryptsetup luksOpen --key-file keyfile /dev/loop0 e1 - * How do I read the LUKS master key from file? The question you should ask yourself first, is why you would want @@ -165,7 +147,6 @@ A. Contributors good reason, please tell me. If I am convinced, I will add how to do this here. - * What are the security requirements for a key read from file? A file-stored key or passphrase has the same security requirements @@ -177,7 +158,6 @@ A. Contributors head -c 256 /dev/random > keyfile - * If I map a journaled file system using dm-crypt/LUKS, does it still provide its usual transactional guarantees? @@ -200,7 +180,6 @@ A. Contributors better with kernel 2.6.36 and the reworking of filesystem flush locking. Kernel 2.6.37 is expected to improve this even further. - * Can I use LUKS or cryptsetup with a more secure (external) medium for key storage, e.g. TPM or a smartcard? @@ -210,7 +189,6 @@ A. Contributors own tool that in turn gets the key from the more secure key storage. - * Can I resize a dm-crypt or LUKS partition? Yes, you can, as neither dm-crypt nor LUKS stores partition size. @@ -229,9 +207,7 @@ A. Contributors encrypted container sizes larger than 2TiB. Use aes-xts-plain64 for that. - -3. Common Problems - + 3. Common Problems * My dm-crypt/LUKS mapping does not work! What general steps are there to investigate the problem? @@ -239,18 +215,17 @@ A. Contributors If you get a specific error message, investigate what it claims first. If not, you may want to check the following things. - - Check that "/dev", including "/dev/mapper/control" is there. If it is - missing, you may have a problem with the "/dev" tree itself or you - may have broken udev rules. + - Check that "/dev", including "/dev/mapper/control" is there. If it + is missing, you may have a problem with the "/dev" tree itself or + you may have broken udev rules. - - Check that you have the device mapper and the crypt target in your kernel. - The output of "dmsetup targets" should list a "crypt" target. If it - is not there or the command fails, add device mapper and - crypt-target to the kernel. - - - Check that the hash-functions and ciphers you want to use are in the kernel. - The output of "cat /proc/crypto" needs to list them. + - Check that you have the device mapper and the crypt target in your + kernel. The output of "dmsetup targets" should list a "crypt" + target. If it is not there or the command fails, add device mapper + and crypt-target to the kernel. + - Check that the hash-functions and ciphers you want to use are in + the kernel. The output of "cat /proc/crypto" needs to list them. * My dm-crypt mapping suddenly stopped when upgrading cryptsetup. @@ -258,7 +233,6 @@ A. Contributors from 1.0.x to 1.1.x). See under "Issues With Specific Versions of cryptsetup". - * When I call cryptsetup from cron/CGI, I get errors about unknown features? @@ -271,7 +245,6 @@ A. Contributors from cron/CGI or the non-shell mechanism to be sure you have the right version. - * Unlocking a LUKS device takes very long. Why? The iteration time for a key-slot (see Section 5 for an explanation @@ -296,7 +269,6 @@ A. Contributors to 10, but it is now derived from the PBKDF2 benchmark as well and set to iterations in 0.125 sec or 1000, whichever is larger. - * "blkid" sees a LUKS UUID and an ext2/swap UUID on the same device. What is wrong? @@ -317,7 +289,6 @@ A. Contributors dd if=/dev/zero of= bs=512 seek=2 count=6 - * cryptsetup segfaults on Gentoo amd64 hardened ... There seems to be some inteference between the hardening and and @@ -326,9 +297,7 @@ A. Contributors other uses, you can apparently specify USE="dynamic" as compile flag, see http://bugs.gentoo.org/show_bug.cgi?id=283470 - -4. Troubleshooting - + 4. Troubleshooting * Can a bad RAM module cause problems? @@ -369,7 +338,6 @@ A. Contributors itself did not report any problems. If you find defect RAM, assume all backups and copied data to be suspect, unless you did a verify. - * How do I test RAM? First you should know that overclocking often makes memory problems @@ -385,10 +353,15 @@ A. Contributors recommend running the following procedure until the first error is found: - - Run Memtest86+ for one cycle - - Run memterster for one cycle (shut down as many other applications as possible) + - Run Memtest86+ for one cycle + + - Run memterster for one cycle (shut down as many other applications + as possible) + - Run Memtest86+ for 24h or more - - Run memtester for 24h or more + + - Run memtester for 24h or more + If all that does not produce error messages, your RAM may be sound, but I have had one weak bit that Memtest86+ needed around 60 hours to find. If you can reproduce the original problem reliably, a good @@ -399,9 +372,7 @@ A. Contributors the settings to the most conservative ones available and try with that. - -5. Security Aspects - + 5. Security Aspects * Should I initialize (overwrite) a new LUKS/dm-crypt partition? @@ -421,7 +392,6 @@ A. Contributors cat /dev/zero > /dev/mapper/e1 dd if=/dev/zero of=/dev/mapper/e1 - * How do I securely erase a LUKS (or other) partition? For LUKS, if you are in a desperate hurry, overwrite the first few @@ -445,7 +415,6 @@ A. Contributors dd_rescue -w /dev/zero /dev/sda10 - * How do I securely erase a backup of a LUKS partition or header? That depends on the medium it is stored on. For HDD and SSD, use @@ -463,12 +432,10 @@ A. Contributors after overwrites. Also write-head alignment issues can lead to data not actually being deleted at all during overwrites. - * What about backup? Does it compromise security? That depends. See next section. - * Why is all my data gone if I overwrite the LUKS header? Overwriting the LUKS header in part or in full is the most common @@ -495,7 +462,6 @@ A. Contributors the running system. Ask on the mailing-list on how to do that and make sure nobody switches off the machine. - * What is a "salt"? A salt is a random key-grade value added to the passphrase before @@ -523,7 +489,6 @@ A. Contributors reasonably-sized salt value (256 bit, e.g.) this is quite infeasible. - * Is LUKS secure with a low-entropy (bad) passphrase? This needs a bit of theory. The quality of your passphrase is @@ -565,7 +530,6 @@ A. Contributors either!) If you add 2 or 3 typos or switch some words around, then this is good passphrase material. - * What is "iteration count" and why is decreasing it a bad idea? Iteration count is the number of PBKDF2 iterations a passphrase is @@ -630,7 +594,6 @@ A. Contributors vulnerable. Lowering it even further increases this danger significantly. - * Is LUKS with default parameters less secure on a slow CPU? Unfortunately, yes. However the only aspect affected is the @@ -654,7 +617,6 @@ A. Contributors passphrases on fast CPUs. Technology can do only so much to compensate for problems in front of the keyboard. - * Why was the default aes-cbc-plain replaced with aes-cbc-essiv? The problem is that cbc-plain has a fingerprint vulnerability, where @@ -682,7 +644,6 @@ A. Contributors encryption key as key. This makes the IV unpredictable without knowing the encryption key and the watermarking attack fails. - * Are there any problems with "plain" IV? What is "plain64"? First, "plain" and "plain64" are both not safe to use with CBC, see @@ -698,7 +659,6 @@ A. Contributors volume sizes <= 2TiB, but not for those > 2TiB. Finally, "plain64" does not cause any performance penalty compared to "plain". - * What about XTS mode? XTS mode is potentially even more secure than cbc-essiv (but only if @@ -717,9 +677,7 @@ A. Contributors LUKS and dm-crypt always use 512B blocks and the issue does not apply. - -6. Backup and Data Recovery - + 6. Backup and Data Recovery * Does a backup compromise security? @@ -762,7 +720,6 @@ A. Contributors scenarios. (Well, you can burn the tape if it is under your control...) - * What happens if I overwrite the start of a LUKS partition or damage the LUKS header or key-slots? @@ -776,7 +733,6 @@ A. Contributors unrecoverable in a cryptographically strong sense, changing about 4-6 bits in random locations of its 128kiB size is quite enough. - * What happens if I (quick) format a LUKS partition? I have not tried the different ways to do this, but very likely you @@ -784,7 +740,6 @@ A. Contributors LUKS header, including the salts. You may also damage the key-slots in part or in full. See also last item. - * What does the on-disk structure of dm-crypt look like? There is none. dm-crypt takes a block device and gives encrypted @@ -797,7 +752,6 @@ A. Contributors dm-crypt device, the damage will be limited to the are you overwrote. - * What does the on-disk structure of LUKS look like? A LUKS partition consists of a header, followed by 8 key-slot @@ -827,7 +781,6 @@ A. Contributors The exact specification of the format is here: http://code.google.com/p/cryptsetup/wiki/Specification - * How do I backup a LUKS header? While you could just copy the appropriate number of bytes from the @@ -839,7 +792,6 @@ A. Contributors cryptsetup luksHeaderBackup --header-backup-file h_bak /dev/mapper/c1 - * How do I backup a LUKS partition? You do a sector-image of the whole partition. This will contain the @@ -854,7 +806,6 @@ A. Contributors a sector image of a partition. Note that compression is ineffective for encrypted data, hence it does not sense to use it. - * Do I need a backup of the full partition? Would the header and key-slots not be enough? @@ -869,7 +820,6 @@ A. Contributors It is highly advisable to have a complete backup to protect against this case. - * Are there security risks from a backup of the LUKS header or a whole LUKS partition? @@ -880,7 +830,6 @@ A. Contributors access, especially if you only erased the LUKS header and not the whole partition. - * I think this is overly complicated. Is there an alternative? Yes, you can use plain dm-crypt. It does not allow multiple @@ -889,9 +838,7 @@ A. Contributors exactly the overwritten parts are lost (rounded up to sector borders). - -7. Issues with Specific Versions of cryptsetup - + 7. Issues with Specific Versions of cryptsetup * When using the create command for plain dm-crypt with cryptsetup 1.1.x, the mapping is incompatible and my data is not accessible @@ -913,7 +860,6 @@ A. Contributors LUKS stores cipher and mode in the metadata on disk, avoiding this problem. - * cryptsetup on SLED 10 has problems... SLED 10 is missing an essential kernel patch for dm-crypt, which @@ -924,4 +870,6 @@ A. Contributors A. Contributors In no particular order: - Arno Wagner + - Milan Broz +