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Note: As mentioned, the other type of encryption next to block-layer encryption is filesystem-level encryption. Following that link, one will also read about some thoughts when either type (block-layer or filesystem-level encryption) might be used. As usual, there is no better in general — it depends on the use case and the environment we are confronted with in a particular situation.
Modern businesses, human rights groups, political minorities, federal agencies, individuals, the military... they all have one thing in common — they want to sustain their integrity, self-determination (links to German site) or maybe just their way of living and/or working by not letting anybody know anything about them. With all the data nowadays stored on computers and the information technologies humans use, all those gadgets and devices have more or less become peoples second brain — certainly, nobody wants anyone else reading his minds.
If we look a little closer, we might find very good and precise reasons why it should be commonsense to encrypt data and why it has to be accepted by anybody. Therefore, we need to take a look at our political as well as social environment and some terms.
Let us introduce two basic terms. Secrecy and privacy. Before you go, look them up somewhere try to answer to yourself, offhanded, what their meaning is. Mostly, when asked instantly, people get it wrong or cannot answer it completely. Another common term among geeks1 but also ordinary people when it comes to computer and modern communication related security is paranoia2. There are more but those three are the ones that suffice in justifying why a group3 of humans would want to use encryption.
Secrecy is the practice of sharing information among a group of people, which can be as small as one person, while hiding it from others. That which is kept hidden is known as the secret. Secrecy is often controversial. Many people claim that, at least in some situations, it is better for everyone if everyone knows all the facts — there should be no secrets. (Wikipedia)
Privacy has no definite boundaries and it has different meanings for different people. It is the ability of an individual or group to keep their lives and personal affairs out of public view, or to control the flow of information about themselves. The right against unsanctioned invasion of privacy by the government, corporations or individuals is part of many countries laws, and in some cases, constitutions or privacy laws. (Wikipedia)
Paranoia is a disturbed thought process characterized by excessive anxiety or fear, often to the point of irrationality and delusion. Paranoid thinking typically includes persecutory beliefs concerning a perceived threat. Paranoia is distinct from phobia, which is more descriptive of an irrational and persistent fear, usually unfounded, of certain situations, objects, animals, activities, or social settings. By contrast, a person suffering paranoia or paranoid delusions tends more to blame or fear others for supposedly intentional actions that somehow affect the afflicted individual. (Wikipedia)
Now that we got a notion about those three terms I am going to introduce another two essential terms — human rights and self-determination — which, by including the above, are just right for deriving the rationale for why encryption is a good thing and by doing so providing an answer to the question of what about the motivation behind encryption is.
And how does all this fit together nicely in order not just only to justify the effort but much more importantly make a stand and claim the right to use encryption for anybody at any times under any circumstances? Well, my point of view is it is all about
We need to look at this term from two different points of view. The first one being the one that tells about the integrity and self-determination focused towards whole nations. The second one, and as I find the more suitable/important point of view with regards to encryption is the one focusing on self-determination on a per individual basis — again, a group of people consisting of at least one person. Self-determination is a central principle of human rights... my understanding of it is:
Humans should be able to realize their own ideas, dreams and desires without being disabled or hassled from the outside. Acting, learning and living in a self-determined manner can be seen as flags of an adult human being that acts in free will, autonomous and responsible not just for himself but also for his environment. That in mind, self-determination is by far not to be confused with arbitrariness and self-righteousness since such behavior would harm a human beings environment and in turn penetrate somebody else "space", decreasing his degree of self-determination.
If you are able to live without breaking this basic principle you might unfortunately be part of a minority. The next section is intended to summarize and finally provide a reasoning why block-layer data encryption is a good thing.
Rationale 1: Now, that we've entered times where governments, arbitrary institutions or corporations as well as individuals4 think they can act against human rights and do whatever they desire in the name of something stupid like the war on terror56 for example, usual folks like you and me see themselves forced to protect their self-determination on their own. To my understanding it is quite commonsense that, in order to be declared a target, somebody needs to know something about you — if he does not (or if he maybe even does not know about your existence which is even better) he can hardly harm you.
Rationale 2: You are no human being. You are what humans call a business. Humans put a lot of effort into you, sometimes they love you, sometimes they hate you but no matter what... they need you and you need them. The reason for your existence is founded and based on the existence of a bunch of humans that march into the same direction by sharing a common mindset and by talking efforts that lead to projected outcomes. You are, more then ever before, subject of a whole variety of substantial threats that may cause damage to you. You, can catch a disease and become ill for example. If you're ill, you loose momentum and so do all the humans representing you as a single unit to the outside world. Nowadays, that you are so much reliant on information and the way you deal with it, if you make mistakes in this regaras, you can become very ill. Not having the correct information at the right times in the right places, pretty much equals problems if not dead.
Rationale 3: To my understanding and from my point of view towards mankind, the third big argument for encryption is balance and saturation. Before we take a look into an encyclopedia let us ask what physics can tell us about saturation. There is a hard believe among physicist that only physical systems with self protection exist. In simple words that means, that there is no linearity in magnitude between a cause and its impact. From a certain point onwards, if the cause grows bigger, the related impact does not grow anymore or at least at such a tiny magnitude that, practically speaking, there can be no more relationship observed between a cause and an impact. All that is shown by the graph below.
A simple example of the above, everybody should be able to realize, is the relation between a humans will (cause) and body movement (impact). One can move his arms around at different speeds — his will can control the speed. He can move his arms not at all, very slow, a little faster, pretty fast and as fast as he can — in fact, everything in between not at all and as fast as he can. Definitely, there is the relationship between his mind (cause) and the speed of his arms moving (impact). The point where one cannot move his arms faster even if he wants to do so, is where the relationship between cause and impact seems to vanish — the curve turns into an horizontal line.
This is self protection since humans are able to imagine moving their arms around with the speed of light but they would simply die by doing so since centrifugal force would be way bigger than the force that keeps arms connected to a humans torso.
Ascertainment 1: We assume, existing systems of any kind know some sort of saturation otherwise they would have already vanished.
Ascertainment 2: In the metaphysical or conceptual sense, balance is used to mean a point between two opposite forces that is desirable over purely one state or the other, such as a balance between the metaphysical Law and Chaos — law by itself being overly controlling, chaos being overly unmanageable, balance being the point that minimizes the negatives of both. (Wikipedia)
So, what has all the saturation and balance stuff to do with block-layer encryption? It helps to keep the balance between rulers and the rest of our species. Block-layer encryption maybe just a tiny but nonetheless an important counterbalance that helps our species keeping balance between chaos9 and total slavery.
Now, after a philosophical journey which some of you might find amusing, others I might have confused and a portion of you is going to throw stones and whiskey bottles (hopefully you emptied them before) at court buildings (please don't do that, better start using block-layer encryption) we should probably get to grips with block-layer encryption. Just a last side blow: If nonetheless you find I am a weirdo and you're with the sane folks, you are either a political leader, you are listed among the richest (which, by the way, couldn't even manage to stop mass starvation, wars nor global climate crisis and the extinction of tons of species etc.) or just not informed enough.
However, do not take my philosophical thoughts to serious since I am a) no professional philosopher, b) not a professional politician (so it's easy to grouch a bit towards those folks) and c) I am not a Listen to me since I am the one and only messiah that can bring you <whatever_you_desire> guy. In fact I am just a free spirit guy who likes to scratch on peoples point of view every now and then...
This section shows some techniques used to encrypt data...
When using block-layer encryption, when the computer boots, the computer asks for a password and/or a keyfile e.g. stored on an USB stick in order to continue booting i.e. loading the operating system. If none or not the correct password is provided, nothing happens. The computer simply refuses to continue with booting thus the data stored on the disk cannot be seen — all information stored on the disk is hidden until somebody provides the correct password/keyfile or both in case of the more paranoid. It is very important that the boot password is complex11 as if the password is simple then the protection of the block-layer encryption is nullified by simple password. A weak passwords always trumps strong security methods.
As the sketch above shows, on the left side a system that uses encryption e.g. dm-crypt and LUKS and on the right side a normal system without encryption. As you can see, the important thing here is that on the left data stored on the computers hard disk drive is encrypted and on the right it is not. The box called Layer providing encryption resp. decryption at the left is where all the magic happens, to whom you provide your password and/or keyfile and which in turn makes any data stored on the disk only available to the person that knows either the correct password and/or has the correct keyfile. Ideally that would be you and only you. In cases, for whatever reason, someone else but you sits in front of your computer, he cannot read your data even if he takes the disk out of your computer and connects it to his own or any other device.
If you do not know about kernel or userspace anyway yet, do not worry, there is no need to in order to create and use an encrypted system — all you need to know is what you want is what the left column shows. If you are using an operating system like Windows, Linux or just love your overpriced Apple thingy and you are not a programmer or the like you are probably looking at something like the image12 below.
There is a layered logic included when using block-layer encryption with dm-crypt. There is a whole variety how one might use block-layer encryption with dm-crypt. One can just encrypt his USB stick, he can encrypt his external USB disk or the internal disk in his computer. The hardware can be as small as an embedded device e.g. some SD card storage on a submarine robot or as huge as a rack-mountable multiprocessor, multicore systems that is installed at a DC (Data Center) which is controlled by staff located in some NOC (Network Operations Center). Our personal computer situation is probably somewhere in between those cases.
One could encrypt a single disk as a whole or just one or more partitions on a single disk. With servers, it is common to use RAID (Redundant Array of Independent Drives (or Disks)) arrays for reasons of increased I/O (Input/Output) and redundancy as well as to ease administration. Those can be in soft- as well as hardware (i.e. a hardware RAID). Adding to all the afore mentioned is the ability to use things like LVM (Logical Volume Manager), EVMS (Enterprise Volume Management System)13 and the like and a variety of filesystems.
A selection of three common examples using dm-crypt:
Before we go into detail with the three examples above, we need to know a little about technical jargon related to our case.
This covers the most common case. A device e.g. computer with a connected hard disk drive or an external USB hard disk drive or maybe something similar to these setups. However, the storage media is split into more than one partition — two in this case (note the free space in between of them — this means nothing else but a portion of the diskspace as not been partitioned15). What the figure also shows is the analogy with regards to the order in that the things are set up. First comes the partition. That follows the crypt device which is then used to create a file system on top of it.
Also, the figure not just only shows HDD but also USB stick, DVD and so on. That is perfectly right — you can use pretty much anything and encrypt the storage space it provides to you. I for example have encrypted my USB stick as well as a partition on my iPod. Further down that page, I will, next to others, use exactly such a setup to show you in detail how to set up and manage a system with dm-crypt16 and LUKS17 resp. cryptsetup to provide block-layer encryption.
The filesystem, which is installed on top of a partition can be any usual file system i.e. BtrFS, Ext2, Ext3, FAT, JFS, NTFS, OCFS2, OpenGFS, ReiserFS, Swap, XFS etc. I use XFS for the most part but will soon be a total BtrFS fan — actually I am already but then this file system is not yet (August 2008) considered finished.
This example differs in one particular point from the former one. It uses another intermediate layer next to dm-crypt which we already know, is responsible for encryption. This additional layer is LVM (Logical Volume Manager). It allows for greater flexibility and system resilience if one decides to use the optional RAID feature set. Both, LVM and dm-crypt are, if in place, virtual block devices within the device-mapper framework of the operating system Linux kernel which are capable of mapping one block device into another — thus creating a bidirectional I/O (Input/Output) chain starting at the plain hardware disk providing storage space, upwards, through virtual block devices into userspace utilization and finally inside RAM (Random Access Memory) and again downwards onto the HDD again and so forth — it is, this is a permanent circulation controlled and managed by the kernel.
This example could be realised as follows: One might use three HDDs installed in his computer (PVs) and create LVs. Thereby, during configuration he decides to use two of the PVs to provide encrypted LVs (LV 1 and LV 2) whereas one of two is additionally configured to provide for RAID 1 (LV 1) (note the mapping from one LE into two PE on different PVs). The third PV (the third HDD in this case) is used to form a non encrypted, non RAID third LV (LV 3) with 1:1 mapping between LEs and PEs as is the case for LV 2.
All three LVs together are part of the same VG and therefore can be managed as a single unit. One could for example move the whole VG to another hardware etc. This however is a simple example. In case you use EVMS (Enterprise Volume Management System) the setup could be much more complex and feature rich.
The filesystem, which is installed on top of LVs devices, can be any usual file system i.e. Ext2, Ext3, FAT, JFS, NTFS, OCFS2, OpenGFS, ReiserFS, BtrFS, Swap, XFS etc.
This one is just to show that things are not necessarily bound to happen on the local machine. Although figure 3 pictures a NAS (Network-attached storage), this can be any kind of storage where data stored on a remote device is accessed by another device and therefore has to travel through a computer network. On the remote site there can be any configuration — either the one depicted in figure 1 or figure 2 which might be an explicit computer configured as a NFS (Network File System) server or a dedicated network appliance18 or any other device running a Linux kernel and thus being able to use dm-crypt.
Mostly, the traffic between remote and local machine does not need to be encrypted since this network should be considered as one to be trusted and not offering access for untrusted people or devices — it is a dedicated network for internal information exchange only, without offering access to the outside world e.g. the Internet (note, that the Internet is not to be confused with the WWW (Wold Wide Web)).
This is when the LVM layer sits on top of the dm-crypt/encryption layer as opposed to what Example 2 shows i.e. LVM layer below encryption layer. I have a few sketches onto another page where I show how it looks like.
This section is about theory — what has to be considered before writing a single line of code for LUKS (crypsetup) or the dm-crypt device-mapper inside the Linux kernel. In essence, it is about mathematics (especially those papers written by Clemens Fruhwirth, the mastermind behind LUKS).
For this part, I decided to just provide the reader with links to some resources since they already describe the issue plus my guess is, that most folks are not going to dive into the deep and wonderful mathematics ocean... those who will, will also prefer to choose their own travel routes thus it would be nonsense trying to provide common itineraries to individual needs and desires.
This section is probably better suited for most folks since it is pretty lightweight but should also satisfy the experienced user.
Is the short for Device Mapper Tables. All device-mappers get there
configuration from simple plaintext files. In case of the dm-crypt
device-mapper, the program
This had been the case before LUKS. With the introduction of LUKS, this two disadvantages where eliminated.
Before LUKS and also now with LUKS, dm-crypt (resp. the Crypt Engine - see below) needs to be provided with a key of fixed length to do en/decryption to/from the encrypted virtual block device. The trick is to use a password in order to compute the key. It is so, that the password can have an arbitrary length but not the key. The key, computed from the password always has the same length (a one-way hash function is used to derive the key from the password). Actually, RIPEMD-160 is used to create the one-way hash.
A screendump to get a notion of what we are talking about:
sa@pc1:/tmp$ echo "fox" | md5sum 475b45b6b3531765210a51ec138af816 - sa@pc1:/tmp$ echo "fox " | md5sum cf1d45ef2ce7d9223ccc6aff89ff7f85 - sa@pc1:/tmp$ echo "The fox wants to eat chicken all day long" | md5sum 16901fc60316999202f01b5c8498420f - sa@pc1:/tmp$ echo "fh&83ka83hz:9('#<)836hT%" | md5sum 6760de41fa137494d8ddd6da9cb14d93 - sa@pc1:/tmp$
Note that the hash19 (e.g.
As of now (July 2007)
,----[ aptitude show cryptsetup | sed -n '/^Description:/,/^Tags/p' - ] | Description: configures encrypted block devices | Since kernel 2.6.4, encrypted file system support is provided by the device | mapper target dm-crypt. This utility provides a command-line interface for | configuring this facility. It has integrated support for LUKS. | | cryptsetup is backwards compatible with the block-layer format of cryptoloop, but | also supports more secure formats. This package also includes support for | automatically configuring encrypted devices at boot time via the config file | /etc/crypttab. When combined with newer versions of the debian initrd-tools and | standard debian kernels, cryptoroot is also supported. | | For information on how to convert your system to use encrypted filesystems | please read /usr/share/doc/cryptsetup/CryptoRoot.HowTo. | | Tags: admin::boot, admin::filesystem, implemented-in::c, interface::commandline, `----
The advantage, with LUKS being part of
Block-layer encryption without (1) and with (2) LUKS:
In both cases an unencrypted block device is taken, subsequently the
dm-crypt device-mapper does its magic and what we get is an encrypted
virtual block device e.g.
The difference in handling block-layer encryption with or without LUKS makes a lot of a difference. There are two dominant parts to think of:
Both, the encrypted information and the information to handle the encrypted information where separated before LUKS and are in the same place now with LUKS (LUKS stores all that information within the partition header of a virtual block device).
So with LUKS, there is a Master Key and it is stored to the partition header of the encrypted virtual block device. That is fine but there is more magic. In fact there can be more ciphertext representations of the Master Key within the partition header. Each one can then be used to de/encrypt data with the encrypted virtual block device. Each of the ciphertext representations of the Master Key can be encrypted with another password thus providing the ability to have a multi-user setup. As of now (July 2007) there are eight so called key slots.
Metainformation now part of the partition header respectively Key Slots:
Quite frankly speaking, if you do that (and folks do that more than you would guess) the best on-diks encryption software and procedure would not help that in the end block-layer encryption would be frail because of the weak password.
Imagine a high security area, surrounded by a compound of impenetrable
barriers and one corridor to move in and out. What are all the
barriers worth when someone finds the secret key to pass the
checkpoint written on the asphalt like that
Salt and stretching is also to avoid the weakness of folks not using
The salting has to ensure that the derived key is not somehow guessable from the password or vice versa. Experts say, the derivation has to provide a high degree of entropy in order to be secure enough.
If the key for example has a length of 128 Bit (thus
possible variations — two
possible conditions (zero and one) and a sequence of 128 Bits) and the
password is a lot smaller e.g. 32 Bit, we end up with (128 - 32) 96
Bit of yet unused space within the key. This 96 Bit could be filled
with either zeros or ones (binary representation). In case we simply
So, 400,000 words... that is a lot from a humans point of view but we need to take another point of view:
sa@pc1:~$ python Python 2.4.4 (#2, Apr 26 2007, 00:02:45) [GCC 4.1.2 20061115 (prerelease) (Debian 4.1.1-21)] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> 2**19 524288 >>> sa@pc1:~$
So with 19 Bits (), what we got is around half a million different keys (words in the dictionary). All we have to do is to write a program that uses all those million words in a dictionary in order to try them as the key for the encrypted hard disk. We are lucky since we do not have to write such a program — there are already many of them on the net, ready for anybody to download and use. The problem is Mr. or Mrs. anybody could also be your worst enemy... As a matter of fact, positively attacking a 20 Bit or so key is possible for anybody with of-the-shelf hardware and even more easily if one has custom hardware available.
PBKDF (Password Based Key Derivation Function) takes care about this in simple but ingenius manner — the computation in order to derive the key from the password has intentionally been made very CPU-intensive. That is absolutely no problem since you, who knows the correct password/keyfile can provide it and subsequently the key gets computed and that is it. Even if it takes one or two seconds (that is very long) it does not really matter. It matters if you had to try it 524288 or 2^19 times. If you have hardware that manages to compute the key in one second, trying to guess the key depends on the key length — thus, it could take up to
sa@pc1:~$ python Python 2.4.4 (#2, Apr 26 2007, 00:02:45) [GCC 4.1.2 20061115 (prerelease) (Debian 4.1.1-21)] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> 524288 / 60 8738 >>> 524288 / (60**2) 145 >>> 524288 / ((60**2) * 24) 6 >>> 2**19 / ((60**2) * 24) 6 >>> 2**20 / ((60**2) * 24) 12 >>> 2**21 / ((60**2) * 24) 24 >>> 2**128 / ((60**2) * 24) 3938453320844195178974243141571391L >>> 2**128 / (((60**2) * 24)* 365) 10790283070806014188970529154990L >>> sa@pc1:~$
As can be seen, half a million attempts would take around six days. It is about twice the time if we just take one more Bit (twenty Bits). With 21 Bits, it would already take 24 days. The last two lines show how long it might take to guess a key with 128 Bits — well, that is more than the age of the universe so I guess a curious person may need a lot of patience. Of course, that example is pretty rough i.e. we did not bring into play mathematics e.g. statistics, probability etc. but for now that is fine and enough to get a notion about how much the key length influences the overall security (secrecy in this case) of encrypted data stored onto a storage device like a hard disk drive for example.
Another advantage that comes with salt is the fact, that if for example two passwords were provided to the KDF (Key Derivation Function) one after another do not result in the same hash (key). That, next to other things, is part of a procedure providing a high degree of entropy.
Again, it is all about the beauty of mathematics i.e. Combinatorics in this case. After the KDF provided us with a high degree of entropy by salting the derivation from the key to the password the user provided, the whole key derivation process is still vulnerable for attacks given enough resources (money, hardware, time, people, brain power, etc.) to the attacker. At this point LUKS introduces stretching. After say 64 of 128 Bit have been mangled by applying salt, the rest of the Bits (128 - 64) which is 64 in this case is not simply padded with zeros or ones but with another random (pseudo-random) value in order to avoid the following.
An attacker could pre-compute all keys (words in a dictionary), store them and later use the stored hash values for guessing the key. In this case he might only compute the hashes (keys) once and later on use them over and over again which reduces the effort from say 6 days to a couple of seconds or so in case of 19 Bits — as you see, this a huge factor; this factor makes it possible to guess the key which in turn renders block-layer encryption useless and probably ensures that ones nightmares become a reality by revealing what should be a secret.
Above, I mentioned that programms to pre-compute all keys in a dictionary exist — just search for them and you will find many of them... but why? You do not have to wait a long time to compute all the keys for different dictionaries since that has already been done — again, search the net and download the result of the computations a brave attacker has already carried out. This pre-computed tables containing all hash keys can be used by any kid in order to attack you, your business etc. With LUKS this is no problem since LUKS takes care about such vulnerability by using salt and padding the key with a pseudorandom value.
With stretching dictionary attacks are impossible since one would have to compute
sa@pc1:~$ python Python 2.4.4 (#2, Apr 26 2007, 00:02:45) [GCC 4.1.2 20061115 (prerelease) (Debian 4.1.1-21)] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> 2**19 524288 >>> 2**(128-19) 649037107316853453566312041152512L >>> (2**(128-19))*(2**19) 340282366920938463463374607431768211456L >>> 2**128 340282366920938463463374607431768211456L >>> sa@pc1:~$
not just all possible keys (words in the dictionary) which we already
know is () but ANY combination
of any key with any number that can be formed of the (128-19) 109 Bits
which we already know is () respectively this absurd long decimal
number above starting with
This section provides a quick look into IT forensics and how it works plus even more importantly, how private persons, companies, governments, military etc. can protect themselves against state of the art techniques uses in IT forensics.
Visitors, Reselling, Dispose
It is common with IT (Information Technology) forensics (e.g. http://www.forensicts.co.uk/ - contractors to Scotland Yard and the like) that HDDs (Hard Disk Drives) are the most important source of information next to network traffic. Whatever you consider a secret, if you use block-layer encryption with dm-crypt then you can be sure that even if your hardware is taken away from you by force, you are save since those folks cannot decrypt the data — thus what is a secret stays a secret as long the password is a secret as well.
Another, more practical use case, is the one where old storage media
is replaced by newer one. Without block-layer encryption this storage
media cannot simply be put on resell or thrown away — anybody could
read the data... Instead, one would have to use tools like
Hard disks drives have a very long remaining memory effect. Even if data appears to be gone, even if the disk has been reinitialised with zeros, even if you invoked the security-erase command of your IDE hard disk, data can be easily recovered. Neither ATA (Advanced Technology Attachment) nor SCSI (Small Computer System Interface) instructions sets provide the opportunity to overwrite old physical sectors which had been in use so far but it then happened that the virtual sector got remapped to yet another physical sector.
Currently (July 2007) believes are that every single Bit has to be
changed (overwritten) at least 40 times in order to withstand state of
the art IT forensic efforts to read data from a storage media. Running
This (the time it takes to overwrite a HDD several times) plus the fact that there are already TiB HDDs available should make it clear to anybody that attempts to destroy information (data as the representation of information) this way (by deleting/overwriting) is nothing but a blind alley.
It is a no brainer that there is neither the time to overwrite data when the doorbell already rings and some curious folks ask you weird stuff nor is there the time to overwrite tens or hundreds of HDDs which are scheduled for disposal or resell.
The only way out of this misery is to use block-layer encryption since with block-layer encryption your data is secure at any times starting with the setup of dm-crypt. If the curious then knock on your door, all you have to do is to pull the plug or if you want the resell your HDD, just do it without concerns — in both cases only you know the password...
Destroying the Key
Assuming we use block-layer encryption with LUKS and dm-crypt, the only thing left to us is to destroy the key we would normally use to decrypt data stored within a virtual block device. This however is a bit tricky since some storage media e.g. HDDs are conceptually designed to avoid the loss of data (which of course is perfectly right). Extra precaution must be taken for this data, since data is not guaranteed to be ever erased.
However, the problem is that the key to unlock the encrypted virtual device is stored to key slots (see above) which fit into a single sector on the disk. The firmware carries out so called sector remapping23. Unintended remapping of sector data is especially bad for key material created via a key hierarchy, as the encrypted key material is typically very short and can be accommodated by a single sector in a reserved remapping zone.
So, if for example, the HDDs firmware remaps a sector and we try to
overwrite the sector afterwards with e.g.
In this case, an attacker (and be sure these guys have the resources, knowledge and will) can equip the HDD with a modified firmware in order to reread old (yet unused) physical sectors again.
LUKS (Linux Unified Key Setup) takes care of the afore mentioned issue as well. How this is accomplished follows subsequently.
The intention of AF Splitting and AF Merging is to not allow IT forensics to recover the key respectively to ensure the key can be securely destroyed if we want to. Such methods are commonly known as AF (Anti-Forensic).
As we already know, in order to make sure we can securely (no chances
to recover) destroy the key on a persistent storage media, using
The smart thing with the AF methods being part of LUKS (Linux Unified Key Setup) is as follows.
What AF Splitting does is quite simple but genius at once. It takes the master-key data and balloons it to about 4000 times of its original size. Roughly speaking, because of the new size, it is necessary to distribute the master-key (here, denoted with the letter x) across the whole HDD (Hard Disk Drive). This leads to the fact that the key is then stored in about 4000 sectors24.
The way those 4000 chunks () are computed is so, that a function computes from . This function ensures for each
At some point, the complete master-key (what it has been before ballooning) is of course needed to unlock/decrypt data stored within the encrypted virtual block device. Any data can be securely destroyed if its not stored in persistent but volatile storage media. Since HDDs are persistent storage media and RAM (Random Access Memory) is not (its volatile) the following is done.
AF Merging is the process of reading all the sectors, each containing a chunk of the 4000 original master-key chunks from HDD into memory and then merging it — all merging takes place inside a computers RAM which guarantees (as with in contrast to HDDs) that it can be deleted securely.
If only one of the 4000 chunks contains incorrect data or is absent, the AF Merging and thus AF (Anti-Forensic) fails entirely.
Because it can be statistically shown, that overwriting one out of 4000 sectors on a HDD (Hard Disk Drive) can be done with almost 100% probability, the AF Splitting/Merging method ensures to be secure against AF (Anti-Forensic) methods and those who use it to reveal your secrets, those of or your business or your country or...
In conjunction with key hierarchies and PBKDF (Password Based Key Derivation Function), LUKS (Linux Unified Key Setup) provides a sophisticated key/password management system which allows to add, delete and change key/keyfiles the secure way (no way for AF (Anti-Forensic) to recover a key).
With the CLI (Command Line Interface) tool
Ciphers used by Dm-Crypt
To really understand dm-crypt and LUKS, it is necessary to take a look at the principles that play a major role when it comes to block-layer encryption. We need to know about the basics of the techniques in place in order to understand what is going on, how it is works and why it is done in a particular way. What exactly is a cipher anyway?
Block Cipher vs Stream Cipher
In cryptography, a block cipher is a symmetric key cipher which operates on fixed-length groups of bits, termed blocks, with an unvarying transformation. When encrypting, a block cipher might take a (for example) 128-bit block of plaintext as input, and output a corresponding 128-bit block of ciphertext. The exact transformation is controlled using a second input — the secret key. Decryption is similar: the decryption algorithm takes, in this example, a 128-bit block of ciphertext together with the secret key, and yields the original 128-bit block of plaintext.
This is in contrast to how a stream cipher works:
In cryptography, a stream cipher is a symmetric cipher where plaintext bits are combined with a pseudorandom cipher bit stream (keystream), typically by an XOR (exclusive-or) operation. In a stream cipher the plaintext digits are encrypted one at a time, and in which the transformation of successive digits varies during the encryption. An alternative name is a state cipher, as the encryption of each digit is dependent on the current state. In practice, the digits are typically single bits or bytes.
Stream ciphers represent a different approach to symmetric encryption from block ciphers. Block ciphers operate on large blocks of digits with a fixed, unvarying transformation.
Because of its nature (dm-crypt works on data blocks), dm-crypt makes use block ciphers and not of stream ciphers.
Block Cipher Modes of Operation
Now, that we know that dm-crypt makes use of block ciphers only, there is still more to know. Block ciphers know several modes of operation. It is not only the cipher in use but also the operation mode the cipher works in that decides what ciphertext is written to the storage media and thus it also has big impact on how secure block-layer encryption is.
Dm-crypt currently (July 2007) allows for two different operation modes:
CBC is preferable (see below why this is true) over ECB but still, both suffer from some security issues which would vanish if LRW-AES (LRW: Liskov, Rivest, Wagner; AES: Advanced Encryption Standard) would be implemented. This however is not done yet because of some issues26 with the Linux Kernel itself.
Electronic Code Book
The simplest of the encryption modes is the electronic codebook (ECB) mode. The message is divided into blocks and each block is encrypted separately. The disadvantage of this method is that identical plaintext blocks are encrypted into identical ciphertext blocks — thus, it does not hide data patterns well. In some senses, it doesn't provide serious message confidentiality, and it is not recommended for use in cryptographic protocols at all.
As mentioned, identical plaintext block lead to identical ciphertext block — this is less secure than what CBC (Cipher Block Chaining) does. Below is a striking example of the degree to which ECB can leave plaintext data patterns in the ciphertext. A pixel-map version of the image on the left was encrypted with ECB mode to create the center image and with CBC to create the right image:
The image on the right is how the image might look like if it had been encrypted with CBC or any of the other more secure modes — indistinguishable from random noise. The center image shows, that same input (plaintext) results in same output (ciphertext) thus ECB is less secure than CBC.
As you might understand now, how secure block-layer encryption is depends not just only on the cipher used but also on the operation mode — the best cipher may produce insecure results if used with a weak mode of operation.
Cipher Block Chaining
In the CBC mode, each block of plaintext is XORed (exclusive-or) with the previous ciphertext block before being encrypted. This way, each ciphertext block is dependent on all plaintext blocks processed up to that point. Also, to make each message unique, an initialization vector must be used in the first block.
CBC has been the most commonly used mode of operation. Its main drawbacks are that encryption is sequential (i.e., it cannot be parallelized), and that the message must be padded to a multiple of the cipher block size27.
Note that a one-bit change in a plaintext affects all following ciphertext blocks, and a plaintext can be recovered from just two adjacent blocks of ciphertext. As a consequence, decryption cannot be parallelized, and a one-bit change to the ciphertext causes complete corruption of the corresponding block of plaintext, and inverts the corresponding bit in the following block of plaintext.
The parallelization issue is one issue that would vanish with the implementation of LRW-AES — this would allow to speed up block-layer encryption on multiprocessor hardware since LRW-AES can do parallel computation of plaintext to ciphertext blocks which is impossible with CBC since block n can only be computed if n-1 has already be done.
One can choose different ciphers when it comes to switch data between its plaintext respectively ciphertext representation in order to unhide/hide information.
We can take a look at the available ciphers
sa@pc1:~$ cat /proc/crypto name : sha256 driver : sha256-generic module : sha256 priority : 0 refcnt : 1 type : digest blocksize : 64 digestsize : 32 name : cbc(aes) driver : cbc(aes-generic) module : cbc priority : 100 refcnt : 3 type : blkcipher blocksize : 16 min keysize : 16 max keysize : 32 ivsize : 16 name : aes driver : aes-generic module : aes priority : 100 refcnt : 5 type : cipher blocksize : 16 min keysize : 16 max keysize : 32 name : md5 driver : md5-generic module : kernel priority : 0 refcnt : 1 type : digest blocksize : 64 digestsize : 16 sa@pc1:~$
Those (the above) are the ciphers which are compiled into the Linux kernel and can be used. Since I use a prepackaged kernel binary,
sa@pc1:~$ uname -a Linux pc1 2.6.21-2-vserver-686#1 SMP Mon Jun 25 23:45:40 UTC 2007 i686 GNU/Linux sa@pc1:~$
the ciphers I may use are fix but that is ok with me since
One is either satisfied with the possible choices or has to compile
his own kernel with additional ciphers. In case he would like to add
additional ciphers, he could use
An IV (Initialization Vector) is a block of bits that is required to allow a stream cipher or a block cipher to be executed in any of several modes of operation to produce a unique ciphertext output independent from other outputs produced by the same encryption key, without having to go through a (usually lengthy) re-keying process.
All block cipher operational modes (except ECB (Electronic Code Book)) require an IV (Initialization Vector) — a sort of dummy block to kick off the process for the first real block, and also to provide some randomization for the process. There is no need for the IV to be secret, in most cases, but it is important that it is never reused with the same key.
For CBC (Cipher Block Chaining) and CFB (Cipher FeedBack), reusing an IV leaks some information about the first block of plaintext, and about any common prefix shared by the two messages. If the IV is chosen at random (which is the case with dm-crypt), the cryptographer must take into consideration the probability of collisions, and if an incremental IV is used as a nonce, the algorithm's resistance to related-IV attacks must also be considered.
For OFB (Output FeedBack) and CTR (Counter), reusing an IV completely destroys security. In CBC mode, the IV must, in addition, be randomly generated at encryption time. (Wikipedia)
More information after the jump...
`n' total number of encrypted sectors `a' sector index `x = a-1' number of ciphertext sectors before sector `a' ENCRYPTION: Each sector `a' depends on `a-1' for encryption -- using the ciphertext of `a-1' and an IV (Initialization Vector). DECRYPTION: In case of decryption, to decrypt ciphertext sector `a', it is only necessary to have ciphertext sector `a-1' around thus the operation is in O(1). It does not require to re-encrypt a number `x' of sectors each time a sector `a' is decrypted thus making it O(n).
In both cases, watermarking attack are becoming impossible since the IV (Initialization Vector) cannot be predicted.
Encrypted Salt-Sector Initialization Vector
ESSIV (Encrypted Salt-Sector Initialization Vector) is a method for generating initialization vectors for block encryption to use in disk encryption. The usual methods for generating IVs are predictable sequences of numbers based on for example time stamp or sector number and permits certain attacks such as a Watermarking attack.
ESSIV on the other hand generates the IV from a combination of the sector number with the hash of the key. It is the combination with the key in form of a hash that makes the IV unpredictable.
Combination of CBC and ESSIV
Finally, if one chooses to use
As I mentioned above, there are two methods to avoid redundant data patterns
The fact that
The questions narrows down to two questions:
sa@pc1:~$ cat /proc/cpuinfo | egrep 'bogo|name|cache' model name : Intel(R) Pentium(R) 4 CPU 3.06Gz cache size : 512 KB bogomips : 6138.51 sa@pc1:~$ su Password: pc1:/home/sa# cryptsetup status /dev/mapper/alan /dev/mapper//dev/mapper/alan is active: cipher: aes-cbc-essiv:sha256 keysize: 128 bits device: /dev/sdd1 offset: 1032 sectors size: 781416570 sectors mode: read/write pc1:/home/sa# hdparm -tT /dev/mapper/alan /dev/mapper/alan: Timing cached reads: 462 MB in 2.00 seconds = 230.93 MB/sec Timing buffered disk reads: 38 MB in 3.05 seconds = 12.45 MB/sec pc1:/home/sa# exit exit sa@pc1:~$
This section is all about getting to grips with block-layer encryption. It is split into several subsections in order to cover different approaches as discussed above with the three examples.
This subsection is about preparations — what needs to be in place in order to start setting up block-layer encryption with some storage media.
We need to have the storage media (e.g. HDD (Hard Disk Drive) or USB (Universal Serial Bus) stick etc.). This storage media will either be used entirely (encrypting the whole storage space) or just partially.
Since setting up block-layer encryption with dm-crypt and random storage media involves overwriting the storage space on the storage media, be aware that all data is irretrievably lost in the course of setting up the virtual block device. Because of that, if the storage media is not yet unused by you but contains data you might want to do a backup to another storage media. Later on, after setting up dm-crypt, you can move the data back onto the storage media — then being outfitted with the dm-crypt device-mapper virtual block device and thus providing transparent en/decryption for I/O (Input/Output) to/from that storage media.
You also need to connect the storage media to a computer or some sort of embedded device built into your pool-cleaning-bot or whatever in order to carry out the setup procedure for dm-crypt. Later on, to use block-layer encryption, the storage media has to be constantly connected to a computer or your bot etc. if you want to use block-layer encryption.
So, it is quite common that folks use one external USB (Universal
Serial Bus) casing with more than one HDD (Hard Disk Drive) to do
Next step after ensuring that the desired hardware is in place, we need to acquire all the software needed to set up and run block-layer encryption with dm-crypt. Basically that means we need to have two things before we can actually start with the setup
If you are with DebianGNU/Linux, all you need to do is to install a
kernel image via Debians outstanding package management system called
,----[ cat ~/.bashrc | grep acsn ] | alias acsn='apt-cache search --names-only' `----
If you want to figure the current pre-build kernel packages with Debian you can do that
sa@pc1:~$ date -u Tue Jul 31 09:36:24 UTC 2007 sa@pc1:~$ finger @kernel.org [kernel.org] The latest stable version of the Linux kernel is: 18.104.22.168 The latest prepatch for the stable Linux kernel tree is: 2.6.23-rc1 The latest snapshot for the stable Linux kernel tree is: 2.6.23-rc1-git9 The latest 2.4 version of the Linux kernel is: 2.4.35 The latest 2.2 version of the Linux kernel is: 2.2.26 The latest prepatch for the 2.2 Linux kernel tree is: 2.2.27-rc2 The latest -mm patch to the stable Linux kernels is: 2.6.23-rc1-mm1 sa@pc1:~$ acsn linux-image-2.6 linux-image-2.6-486 - Linux 2.6 image on x86 linux-image-2.6-686 - Linux 2.6 image on PPro/Celeron/PII/PIII/P4 linux-image-2.6-686-bigmem - Linux 2.6 image on PPro/Celeron/PII/PIII/P4 linux-image-2.6-amd64 - Linux 2.6 image on AMD64 linux-image-2.6-k7 - Linux 2.6 image on AMD K7 linux-image-2.6-vserver-686 - Linux 2.6 image on PPro/Celeron/PII/PIII/P4 linux-image-2.6-vserver-k7 - Linux 2.6 image on AMD K7 linux-image-2.6.21-2-486 - Linux 2.6.21 image on x86 linux-image-2.6.21-2-686 - Linux 2.6.21 image on PPro/Celeron/PII/PIII/P4 linux-image-2.6.21-2-686-bigmem - Linux 2.6.21 image on PPro/Celeron/PII/PIII/P4 linux-image-2.6.21-2-amd64 - Linux 2.6.21 image on AMD64 linux-image-2.6.21-2-k7 - Linux 2.6.21 image on AMD K7 linux-image-2.6.21-2-vserver-686 - Linux 2.6.21 image on PPro/Celeron/PII/PIII/P4 linux-image-2.6.21-2-vserver-k7 - Linux 2.6.21 image on AMD K7 linux-image-2.6.22-1-486 - Linux 2.6.22 image on x86 linux-image-2.6.22-1-686 - Linux 2.6.22 image on PPro/Celeron/PII/PIII/P4 linux-image-2.6.22-1-686-bigmem - Linux 2.6.22 image on PPro/Celeron/PII/PIII/P4 linux-image-2.6.22-1-amd64 - Linux 2.6.22 image on AMD64 linux-image-2.6.22-1-k7 - Linux 2.6.22 image on AMD K7 linux-image-2.6.22-1-vserver-686 - Linux 2.6.22 image on PPro/Celeron/PII/PIII/P4 linux-image-2.6.22-1-vserver-k7 - Linux 2.6.22 image on AMD K7 linux-image-2.6.22-rc7-486 - Linux 2.6.22-rc7 image on x86 linux-image-2.6.22-rc7-686 - Linux 2.6.22-rc7 image on PPro/Celeron/PII/PIII/P4 linux-image-2.6.22-rc7-686-bigmem - Linux 2.6.22-rc7 image on PPro/Celeron/PII/PIII/P4 linux-image-2.6.22-rc7-amd64 - Linux 2.6.22-rc7 image on AMD64 linux-image-2.6.22-rc7-k7 - Linux 2.6.22-rc7 image on AMD K7 sa@pc1:~$
The first few lines are merely because I just wanted to show that
Debians pre-build kernel packages are not outdated but pretty much
up-to-date — you can see, the current stable Linux kernel is at
,----[ grep -A1 '^# kernel' /etc/apt/sources.list ] | # kernel snapshots - sid | deb http://kernel-archive.buildserver.net/debian-kernel sid main | -- | # kernel snapshots - trunk (= most up-to-date and risky) | deb http://kernel-archive.buildserver.net/debian-kernel trunk main `----
sa@pc1:~$ aptitude search linux-image-2.6.*vserver p linux-image-2.6-vserver-686 - Linux 2.6 image on PPro/Celeron/PII/PIII/P4 p linux-image-2.6-vserver-k7 - Linux 2.6 image on AMD K7 c linux-image-2.6.17-2-vserver-686 - Linux 2.6.17 image on PPro/Celeron/PII/PIII/P4 c linux-image-2.6.18-4-vserver-686 - Linux 2.6.18 image on PPro/Celeron/PII/PIII/P4 c linux-image-2.6.20-1-vserver-686 - Linux 2.6.20 image on PPro/Celeron/PII/PIII/P4 i linux-image-2.6.21-2-vserver-686 - Linux 2.6.21 image on PPro/Celeron/PII/PIII/P4 p linux-image-2.6.21-2-vserver-k7 - Linux 2.6.21 image on AMD K7 C linux-image-2.6.22-1-vserver-686 - Linux 2.6.22 image on PPro/Celeron/PII/PIII/P4 p linux-image-2.6.22-1-vserver-k7 - Linux 2.6.22 image on AMD K7 sa@pc1:~$
However, no matter what pre-build kernel package you install, all come with dm-crypt and LUKS (Linux Unified Key Setup) support enabled
,----[ grep DM_CRYPT /boot/config-2.6.22-1-vserver-686 ] | CONFIG_DM_CRYPT=m `----
As you can see, I am currently on
,----[ uname -a ] | Linux pc1 2.6.22-1-vserver-686 #1 SMP Mon Jul 30 03:18:43 UTC 2007 i686 GNU/Linux `----
Finally, if you want to or have to for some special reason, you can
always get the vanilla sources from
Now that we know what pre-build kernel binaries are available, we need
to install what we considered suitable for our environment. I am going
with current DebianGNU/Linux unstable branch (aka sid (still in
development)) kernels on my workstation and mobile gadgets. If you
would like to install a pre-build kernel image, you would have to
Now that we have got a Linux kernel with support for dm-crypt, our
further needs are the userspace tools to set up and manage dm-crypt
virtual block devices. I am going to become
sa@pc1:~$ su Password: pc1:/home/sa# aptitude -s install cryptsetup Reading package lists... Done Building dependency tree... Done Reading extended state information Initializing package states... Done Reading task descriptions... Done Building tag database... Done The following packages have been kept back: python-twisted-web 0 packages upgraded, 0 newly installed, 0 to remove and 1 not upgraded. Need to get 0B of archives. After unpacking 0B will be used. Would download/install/remove packages. pc1:/home/sa# apt-get -s install cryptsetup Reading package lists... Done Building dependency tree... Done cryptsetup is already the newest version. 0 upgraded, 0 newly installed, 0 to remove and 1 not upgraded. pc1:/home/sa#
So, nothing had been installed here but that is perfectly right since
Installing a package with Debians package management system is quite
comforting since it takes care of all dependencies — the package and
its dependencies are getting installed whenever you use a front-end
,----[ apt-cache depends cryptsetup ] | cryptsetup | Depends: libc6 | Depends: libdevmapper1.02.1 | Depends: libgcrypt11 | Depends: libpopt0 | Depends: libuuid1 | Depends: dmsetup | Suggests: udev | |Suggests: initramfs-tools | Suggests: <linux-initramfs-tool> | initramfs-tools | yaird | Suggests: dosfstools | Conflicts: <cryptsetup-luks> | Conflicts: hashalot | Replaces: <cryptsetup-luks> `----
pc1:/home/sa# cryptsetup --version cryptsetup 1.0.5 pc1:/home/sa#
and the package version
sa@pc1:~$ dpl cryptse* | grep ^ii ii cryptsetup 2:1.0.5-1 configures encrypted block devices sa@pc1:~$
At a side note, you might have noticed I became the normal user
,----[ whoami ] | sa `----
again — I issued
Finally, another not essential but nice to have tool is
A tool which I use pretty often but which is not necessarily needed
pc1:/home/sa# exit exit sa@pc1:~$ apt-file search sfdisk | grep bin/ | cut -d ':' -f1 | xargs dpkg -l | grep ^ii ii util-linux 2.12r-19 Miscellaneous system utilities sa@pc1:~$
Therefore, you might want to install
sa@pc1:~$ afs badblocks | grep bin/ e2fsprogs: sbin/badblocks mtools: usr/bin/mbadblocks sa@pc1:~$
At that point, the software we need
should be in place. We can now start to set up dm-crypt on some storage media. Whatever the storage media will be, we need to make first contact so to say. We need to either figure some pci bus id or try it on another, preferably higher level.
Hard Disk Drive - external or internal
In case we would use a HDD (Hard Disk Drive)
pc1:/home/sa# fdisk -l | grep ^Disk Disk /dev/md0 doesn't contain a valid partition table Disk /dev/hda: 60.0 GB, 60011642880 bytes Disk /dev/hdb: 60.0 GB, 60011642880 bytes Disk /dev/md0: 24.9 GB, 24996478976 bytes Disk /dev/dm-1 doesn't contain a valid partition table Disk /dev/dm-0 doesn't contain a valid partition table Disk /dev/sdb: 400.0 GB, 400088457216 bytes Disk /dev/dm-1: 400.0 GB, 400085283840 bytes Disk /dev/sdd: 251.0 GB, 251000193024 bytes Disk /dev/dm-0: 250.9 GB, 250993858560 bytes pc1:/home/sa#
would be a good choice. Using fdisk, one would just have to look at the HDD sizes shown and then find the match to the HDD he wants to use for block-layer encryption. I got two external USB (Universal Serial Bus) HDDs, one 400GB and the other one 250GB.
The screendump above has been made with already mounted HDDs
providing block-layer encryption. However, in both cases, after the
mounting and with not already mounted HDDs the lines
Universal Serial Bus Sticks, Card Readers, iPods...
In case we are not dealing with some HDD (Hard Disk Drive) but some other sort of storage media, we probably need to drill a little bit deeper into the system.
PCI Bus Identifier
To take a look at what devices are connected to the PCI bus one might
1. You know the name of your hardware — manufacturer, vendor, reseller etc. and then the device usually has got a type identifier.
2. With that information you can look up the unique PCI bus ID (Identifier) since any manufacturer got his range of IDs and therefore assigns unique IDs to his devices. There is a file around that lists devices and their PCI IDs. It is called
sa@pc1:~$ locate pci.ids /usr/share/misc/pci.ids /usr/share/hwdata/pci.ids sa@pc1:~$
and comes with those packages
sa@pc1:~$ afs pci.ids hwdata: usr/share/hwdata/pci.ids pciutils: usr/share/misc/pci.ids sa@pc1:~$
The most up-to-date
sa@pc1:~$ cd /tmp/ sa@pc1:/tmp$ curl -O http://pciids.sourceforge.net/pci.ids % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 100 456k 100 456k 0 0 112k 0 0:00:04 0:00:04 --:--:-- 148k sa@pc1:/tmp$ head -n15 pci.ids # # List of PCI IDs # # Maintained by Martin Mares <firstname.lastname@example.org> and other volunteers from the # Linux PCI IDs Project at http://pciids.sf.net/. # # New data are always welcome, especially if accurate. If you have # anything to contribute, please follow the instructions at the web site # or send a diff -u against the most recent pci.ids to email@example.com. # # This file can be distributed under either the GNU General Public License # (version 2 or higher) or the 3-clause BSD License. # # Daily snapshot on Wed 2007-08-01 01:05:01 # sa@pc1:/tmp$
As you can see, there are daily snapshots — current date is
pc1:/home/sa# update-pciids % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 100 119k 100 119k 0 0 63413 0 0:00:01 0:00:01 --:--:-- 93916 Done. pc1:/home/sa#
which is part of the
3. Now that you know the PCI ID from
Therefore, if we plug some storage media to the computer and instantly
sa@pc1:~$ su Password: pc1:/home/sa# dmesg | grep -v bound =UDP SPT=45549 DPT=1027 LEN=486 agpgart: Found an AGP 2.0 compliant device at 0000:00:00.0. agpgart: Putting AGP V2 device at 0000:00:00.0 into 1x mode agpgart: Putting AGP V2 device at 0000:01:00.0 into 1x mode [drm] Loading R200 Microcode usb 6-4: USB disconnect, address 6 pc1:/home/sa# dmesg | grep -v bound .39.210 LEN=56 TOS=0x00 PREC=0x00 TTL=122 ID=602 PROTO=UDP SPT=39931 DPT=43719 LEN=36 agpgart: Found an AGP 2.0 compliant device at 0000:00:00.0. agpgart: Putting AGP V2 device at 0000:00:00.0 into 1x mode agpgart: Putting AGP V2 device at 0000:01:00.0 into 1x mode [drm] Loading R200 Microcode usb 6-4: USB disconnect, address 6 usb 6-3: new high speed USB device using ehci_hcd and address 7 usb 6-3: configuration #1 chosen from 1 choice scsi6 : SCSI emulation for USB Mass Storage devices usb-storage: device found at 7 usb-storage: waiting for device to settle before scanning usb-storage: device scan complete scsi 6:0:0:0: Direct-Access Maxtor 6 L250R0 0000 PQ: 0 ANSI: 0 SCSI device sdd: 490234752 512-byte hdwr sectors (251000 MB) sdd: Write Protect is off sdd: Mode Sense: 27 00 00 00 sdd: assuming drive cache: write through SCSI device sdd: 490234752 512-byte hdwr sectors (251000 MB) sdd: Write Protect is off sdd: Mode Sense: 27 00 00 00 sdd: assuming drive cache: write through sdd: unknown partition table sd 6:0:0:0: Attached scsi disk sdd pc1:/home/sa#
There are two things to mention regarding the screendump above
This section is about setting up block-layer encryption with HDDs (Hard Disk Drives). External (e.g. connected via USB or FireWire) or internal (connected via PATA (Parallel ATA) or SATA (Serial ATA) respectively SAS (Serial Attached SCSI) interfaces).
External Universal Serial Bus Hard Disk Drive
It is a good idea to check the entire HDD for errors before we start. Not only is this good practise, but also, modern hard disks contain a few spare sectors, and if we detect I/O (Input/Output) errors, bad sectors are silently replaced with spare sectors (this is invisible to the OS (Operating System)). So writing and reading the entire disk before we start should allow this mapping from bad to spare sectors to happen.
This step is optional but I strongly recommend to not skip it since it ensures the HDD has got no erroneous sectors plus it writes random data onto the HDD and thus is an AF (Anti-Forensic) countermeasure.
The following command checks the HDD for bad sectors and fills it with pseudo-random data.
pc1:/home/sa# badblocks -c 10240 -s -w -t random -v /dev/sdd
Be aware of the fact, that it takes around 180 minutes per 100GiB depending on your computers speed (generating random data is very CPU intensive). For a 400GB HDD it will probably take the whole night to complete, so trigger the process before you go to bed or so.
This step is also optional. Although, I strongly recommended to not skip the former step, this one is not absolutely necessary. The above example fills the HDD with pseudo-random data, thus the degree of randomness is eventually not enough to withstand an expert forensic attack.
For those of you who would set up a logical virtual block device, with the most possible strength, should carry out another step after the afore mentioned checking for bad sectors and filling with pseudo-random data.
pc1:/home/sa# dd if=/dev/urandom of=/dev/sdd
This also takes a long time — around 3 minutes per GiB on my 5 years old 32 Bit system.
sa@pc1:~$ cat /proc/cpuinfo | grep 'model name' model name : Intel(R) Pentium(R) 4 CPU 3.06GHz sa@pc1:~$
For a 400GB (~372 GiB) that takes around
sa@pc1:~$ python Python 2.4.4 (#2, Jul 21 2007, 11:00:24) [GCC 4.1.3 20070718 (prerelease) (Debian 4.1.2-14)] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> (372*3)/60 18 >>> sa@pc1:~$
hours. For that, I used one of my other computers but not my
workstation. We can use tools such as
sa@sub:~$ type acsn; acsn pv | grep '^pv ' acsn is aliased to `apt-cache search --names-only' pv - Shell pipeline element to meter data passing through sa@sub:/tmp$ acsn bar | grep '^bar ' bar - Show information about a data transfer
Now, just to demonstrate it, we will use the file
sa@sub:/tmp$ dd bs=1M count=100 if=/dev/urandom | bar -s 100m -of /tmp/foobar 68+1 records in 8MB/s eta: 0:00:06 64% [====================================== ] 68+0 records out 71303168 bytes (71 MB) copied, 11.1042 s, 6.4 MB/s [ a snapshot at 64% ...] sa@sub:/tmp$ ll foobar; file foobar -rw-r--r-- 1 sa sa 100M Jul 4 00:12 foobar foobar: data sa@sub:/tmp$
As can be seen, block-layer encryption already starts before there is any encryption software (dm-crypt in our case) in place. It is important to initially fill the storage media with pseudo-random data!
Partitioning the Hard Disk Drive
Folks are mostly familiar using
sa@pc1:~$ su Password: pc1:/home/sa# fdisk /dev/sdd The number of cylinders for this disk is set to 30515. There is nothing wrong with that, but this is larger than 1024, and could in certain setups cause problems with: 1) software that runs at boot time (e.g., old versions of LILO) 2) booting and partitioning software from other OSs (e.g., DOS FDISK, OS/2 FDISK) Command (m for help): p Disk /dev/sdd: 251.0 GB, 251000193024 bytes 255 heads, 63 sectors/track, 30515 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Device Boot Start End Blocks Id System Command (m for help): n Command action e extended p primary partition (1-4) p Partition number (1-4): 1 First cylinder (1-30515, default 1): 1 Last cylinder or +size or +sizeM or +sizeK (1-30515, default 30515): Using default value 30515 Command (m for help): p Disk /dev/sdd: 251.0 GB, 251000193024 bytes 255 heads, 63 sectors/track, 30515 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Device Boot Start End Blocks Id System /dev/sdd1 1 30515 245111706 83 Linux Command (m for help): w The partition table has been altered! Calling ioctl() to re-read partition table. Syncing disks. pc1:/home/sa#
That way I partitioned the HDD to provide a single partition that
spans the whole physically available storage space. The user input I
provided was as follows (a ordered sequence):
1 pc1:/tmp/our_tmp_dir# sfdisk /dev/sdc << EOF 2 > ,1,0,* 3 > ,330,B,* 4 > ,,83,- 5 >Checking that no-one is using this disk right now... 6 OK 7 8 Disk /dev/sdc: 497 cylinders, 255 heads, 63 sectors/track 9 Old situation: 10 Units = cylinders of 8225280 bytes, blocks of 1024 bytes, counting from 0 11 12 Device Boot Start End #cyls #blocks Id System 13 /dev/sdc1 * 0+ 4 5- 40131 0 Empty 14 /dev/sdc2 * 5 496 492 3951990 b W95 FAT32 15 /dev/sdc3 0 - 0 0 0 Empty 16 /dev/sdc4 0 - 0 0 0 Empty 17 New situation: 18 Units = cylinders of 8225280 bytes, blocks of 1024 bytes, counting from 0 19 20 Device Boot Start End #cyls #blocks Id System 21 /dev/sdc1 * 0+ 0 1- 8032 0 Empty 22 /dev/sdc2 * 1 330 330 2650725 b W95 FAT32 23 /dev/sdc3 331 496 166 1333395 83 Linux 24 /dev/sdc4 0 - 0 0 0 Empty 25 Warning: more than one primary partition is marked bootable (active) 26 This does not matter for LILO, but the DOS MBR will not boot this disk. 27 Successfully wrote the new partition table 28 29 Re-reading the partition table... 30 31 If you created or changed a DOS partition, /dev/foo7, say, then use dd(1) 32 to zero the first 512 bytes: dd if=/dev/zero of=/dev/foo7 bs=512 count=1 33 (See fdisk(8).)
In lines 1 to 33, we are creating new partitions on the iPods HDD —
my iPod runs Linux that is why. Therefor, I use
Line 12 to 16 shows the old situation. Line 20 to 24 shows the new
situation, which, what is the result of line 1 to 4. If you enter
those lines on the CLI (Command Line Interface), you can signal an
Below is a listing of the available partition types:
Each partition, regardless if primary or logical partition, can have
it is own file system type e.g.
01 FAT12 24 NEC DOS 81 Minix / old Linux C1 DRDOS/sec (FAT-12) 02 XENIX root 39 Plan 9 82 Linux swap / Solaris C4 DRDOS/sec (FAT-16 < 03 XENIX usr 3C PartitionMagic recov 83 Linux C6 DRDOS/sec (FAT-16) 04 FAT16 <32M 40 Venix 80286 84 OS/2 hidden C: drive C7 Syrinx 05 Extended 41 PPC PReP Boot 85 Linux extended DA Non-FS data 06 FAT16 42 SFS 86 NTFS volume set DB CP/M / CTOS /... 07 HPFS/NTFS 4D QNX4.x 87 NTFS volume set DE Dell Utility 08 AIX 4E QNX4.x 2nd part 88 Linux plaintext DF BootIt 09 AIX bootable 4F QNX4.x 3rd part 8E Linux LVM E1 DOS access 0A OS/2 Boot Manager 50 OnTrack DM 93 Amoeba E3 DOS R/O 0B W95 FAT32 51 OnTrack DM6 Aux1 94 Amoeba BBT E4 SpeedStor 0C W95 FAT32 (LBA) 52 CP/M 9F BSD/OS EB BeOS fs 0E W95 FAT16 (LBA) 53 OnTrack DM6 Aux3 A0 IBM Thinkpad hiberna EE EFI GPT 0F W95 Ext'd (LBA) 54 OnTrackDM6 A5 FreeBSD EF EFI (FAT-12/16/32) 10 OPUS 55 EZ-Drive A6 OpenBSD F0 Linux/PA-RISC boot 11 Hidden FAT12 56 Golden Bow A7 NeXTSTEP F1 SpeedStor 12 Compaq diagnostics 5C Priam Edisk A8 Darwin UFS F4 SpeedStor 14 Hidden FAT16 <32M 61 SpeedStor A9 NetBSD F2 DOS secondary 16 Hidden FAT16 63 GNU HURD or SysV AB Darwin boot FD Linux raid autodetec 17 Hidden HPFS/NTFS 64 Novell Netware 286 B7 BSDI fs FE LANstep 18 AST SmartSleep 65 Novell Netware 386 B8 BSDI swap FF BBT 1B Hidden W95 FAT32 70 DiskSecure Multi-Boo BB Boot Wizard hidden 1C Hidden W95 FAT32 (LBA) 75 PC/IX BE Solaris boot 1E Hidden W95 FAT16 (LBA) 80 Old Minix BF Solaris
We are now ready to create the logical virtual block device also known as dm-crypt device-mapper device.
dm-crypt works by transparently translating32 (within the kernel) between a physical block-layer partition (which is encrypted) and a logical partition (the logical virtual block device) which we can then mount and use as usual.
We know my external USB (Universal Serial Bus) HDD is at
pc1:/home/sa# cryptsetup --verbose -c aes-cbc-essiv:sha256 --verify-passphrase luksFormat /dev/sdd1 WARNING! ======== This will overwrite data on /dev/sdd1 irrevocably. Are you sure? (Type uppercase yes): YES Enter LUKS passphrase: Verify passphrase:
in order to format (
If you prefer to use a key-file, you might study the possibilities
reading the manual page (
pc1:/home/sa# cryptsetup -v --cipher serpent-cbc-essiv:sha256 --key-size 256 luksFormat /dev/sdd1 <keyfile>
The alert reader might have noticed that I used
The logical virtual block device is then ready to be opened33. After
opening it by providing the correct password (line 2), I decided to
take a look (
1 pc1:/home/sa# cryptsetup luksOpen /dev/sdd1 kim 2 Enter LUKS passphrase: 3 key slot 0 unlocked. 4 Command successful. 5 pc1:/home/sa# ls -l /dev/mapper/ 6 total 0 7 brw-rw---- 1 root disk 253, 1 2007-07-31 14:49 alan 8 crw-rw---- 1 root root 10, 63 2007-07-31 12:01 control 9 brw-rw---- 1 root disk 253, 0 2007-07-31 14:48 kim 10 pc1:/home/sa#
As can be seen, in line 1 I issued the command to open the encrypted
HDD and therefore it is now providing the logical virtual block device
The next step is to create a file system on top of the logical virtual
block device. This is just like making a normal file system, we need
I use Ext3 respectively Ext4
pc1:/home/sa# mkfs.ext3 -j -m 1 -O dir_index,filetype,sparse_super /dev/mapper/kim
but do have a fond for XFS
pc1:/home/sa# mkfs.xfs /dev/mapper/kim
you might also download the tools to manage a XFS file system
,----[ dpkg -l xfs* | grep ^ii ] | ii xfsdump 2.2.45-1 Administrative utilities for the XFS filesys | ii xfsprogs 2.9.0-1 Utilities for managing the XFS filesystem `----
As I said, one might use any file system with all provided options — nothing differs from the usual case of creating a file system on storage media providing plain I/O (Input/Output) without any kind of block-layer encryption.
This is just like a normal mount, except we use the logical
1 pc1:/home/sa# fdisk -l | grep ^Disk 2 Disk /dev/md0 doesn't contain a valid partition table 3 Disk /dev/dm-0 doesn't contain a valid partition table 4 Disk /dev/dm-1 doesn't contain a valid partition table 5 Disk /dev/hda: 60.0 GB, 60011642880 bytes 6 Disk /dev/hdb: 60.0 GB, 60011642880 bytes 7 Disk /dev/md0: 24.9 GB, 24996478976 bytes 8 Disk /dev/sda: 251.0 GB, 251000193024 bytes 9 Disk /dev/dm-0: 250.9 GB, 250993858560 bytes 10 Disk /dev/sdd: 400.0 GB, 400088457216 bytes 11 Disk /dev/dm-1: 400.0 GB, 400085283840 bytes 12 pc1:/home/sa# cryptsetup luksOpen /dev/sda1 kim 13 Enter LUKS passphrase: 14 key slot 0 unlocked. 15 Command successful. 16 pc1:/home/sa# mount /dev/mapper/kim /media/usb0 17 pc1:/home/sa# exit 18 exit 19 sa@pc1:~$
The only thing to note here is, that with
,----[ di -h | head -n1 && di -h | grep media ] | File System Mount Size Used Avail %Used fs Type | /dev/dm-0 /media/disk 233.6G 140.5G 93.1G 60% xfs | /dev/dm-1 /media/disk-1 372.5G 340.4G 32.1G 91% xfs | /dev/mapper/kim /media/usb0 233.6G 140.5G 93.1G 60% xfs | /dev/mapper/alan /media/usb1 372.5G 340.4G 32.1G 91% xfs `----
As we can see, one disk and two mount points. Also, note the
size difference reported by
We are done. Now we have another 233GiB (~250GB) of storage media at our hands to keep was is a secret a secret and thus maintaining our self-determination, securing our business, the governmental agency can fulfill imposts it has to obey to or we can equip the UMPC (Ultra-Mobile PC) the brave soldiers carry around on the 21st century battlefield with an encrypted HDD (Hard Disk Drive) or SSD (Solid State Drive).
After using the logical virtual block device we need to unmount and close the device again. It is important to close the device in order to avoid the following
The below screendump shows, both,
pc1:/home/sa# ls -l /dev/mapper/ total 0 brw-rw---- 1 root disk 253, 1 2007-08-03 05:55 alan crw-rw---- 1 root root 10, 63 2007-08-03 05:42 control brw-rw---- 1 root disk 253, 0 2007-08-03 05:51 kim pc1:/home/sa#
So, the device needs to be closed. Before closing it, it must be unmounted which can be done via the GUI (Graphical User Interface).
Note the two different icons per HDD. I noted above that I mounted the
HDD to a second mount point — so there they are as can be seen. When
I want to unmount a HDD, I have to click both icons per HDD and use
the menu item
The second choice next to the GUI is to use the CLI (Command Line Interface). Again, please note that I had chosen to mount the logical virtual block device twice thus the double umount.
pc1:/home/sa# umount /media/usb0 pc1:/home/sa# umount /media/disk pc1:/home/sa#
Finally, the current status is that both former devices
pc1:/home/sa# ls -l /dev/mapper/ total 0 brw-rw---- 1 root disk 253, 1 2007-08-03 05:55 alan crw-rw---- 1 root root 10, 63 2007-08-03 05:42 control brw-rw---- 1 root disk 253, 0 2007-08-03 05:51 kim pc1:/home/sa# cryptsetup luksClose kim pc1:/home/sa# ls -l /dev/mapper/ total 0 brw-rw---- 1 root disk 253, 1 2007-08-03 05:55 alan crw-rw---- 1 root root 10, 63 2007-08-03 05:42 control pc1:/home/sa#
For now we have been talking about static storage sizes which had then been encrypted. What if it becomes necessary to resize (grow/shrink) the file system and its underlying logical virtual block device?
No problem. We are going to put another layer below the whole block-layer encrypted shebang. This additional layer is called LVM (Logical Volume Manager) and is the Linux implementation providing us with storage virtualization. This whole subject (block-layer encryption on top LVM) is covered on my dedicated LVM page.
I strongly recommend for using block-layer encryption on top of LVM for all practical purposes! Why this combination is generally considered best-practice can be read on my dedicated LVM page and on this page respectively. In short, LVM is needed to provide a flexible storage layer and block-layer encryption to keep a secrets and protect assets from others.
This combined subject (block-layer encryption + LVM) may sound complex and huge at first glance but then, I am providing very good information I think — even the novice can deal with easy-to-ape information as I am used to write this whole website/platform. So, anybody go for block-layer encryption atop LVM now! ;-]
In this section, I am going to show how to use dm-crypt and LUKS to encrypt some hardware RAID array which is managed with Adaptec's 31205 PCIe (PCI Express) RAID HBA (Host Bus Adapter) controller. This PCIe controller can manage up to 12 SATA/SAS (Serial Attached SCSI) HDDs whereas one might mix SATA and SAS HDDs although it is recommended not to do so for performance reasons and the like. I am just using SATA HDDs in this server.
I also strongly recommend the use of LVM (Logical Volume Manager) at a lower level in order to do online expansion etc. of some hardware RAID array that one intends to fully encrypt. We can then build our logical encrypted block device atop (see above) the LVM layer. In fact, I make use of LVM all the time — even for external USB HDDs.
Hardware RAID + LVM + Block-layer Encryption
There are two different ways to do this — the straight forward one and the more flexible but also more complicated one.
Installation from Scratch
We have a computer (e.g. workstation) into which we installed a RAID HBA (Host Bus Adapter) card with some HDDs connected to it. There is no OS (Operating System) installed so far, just the hardware is assembled and ready to go. Next we initialize the RAID array, make it bootable and install DebianGNU/Linux onto that RAID array, all as usual.
The actual work i.e. setting up block-layer encryption with LVM on top of our hardware RAID is done by the Debian installer. Yes, it really is that easy! All we need to do after we have initialized and made the RAID array bootable is to for example use a netinstall image and install Debian. Finally, we end up with a setup as mentioned in example 4 from above.
OS already installed
The second case is where we already have an up and running system i.e. some computer with Debian installed plus there is also a RAID HBA card installed into the system. In this case, there are two possible ways to proceed depending on the yet existing setup.
Actually, for us it does not matter which case our yet existing setup is because from now on, the procedure is the same for both. However, now we face the choice between putting the
Both have their particular weaknesses and strengths as I stated here. Bellow follows a listing of all the necessary steps (in chronological order) needed to accomplish our goal which is to use a RAID array with LVM and dm-crypt/LUKS.
It is always the same, we pick a block device (HDD, USB stick, RAID array, LUN (Logical Unit Number), etc.) put our layers (storage e.g. LVM, encryption e.g. dm-crypt, backup e.g. DRBD, etc.) in some particular order onto it. Finally we put a file system on top of the whole stack and be done.
Growing the Storage
Of course there are differences between SSDs (Solid State Drives) and HDDs (Hard Disk Drives) but not so much with regard to block-layer encryption. SSDs are completely different in design to HDDs. However, both can be used in the same way (as a storage media connected to the same I/O (Input/Output) interface type e.g. SATA (Serial ATA)). Because they can be used in the same way and thus become quite transparent to the OS (Operating System) (roughly speaking) the following is true.
The bottom line is, neither with HDDs (Hard Disk Drives) nor SSDs (Solid State Drives) need we fear our secrets may be revealed.... as long as we use block-layer encryption.
This works exactly the same as to what I already mentioned above. The only difference is that now we deal with some USB stick instead of some HDD.
The easiest way to accomplish an encrypted swap partition is when we use the Debian installer and choose to have and encrypted swap partition. The installer does all the magic and sets it up in the process of installing Debian.
On the other hand, should we already have an up and running system with Debian installed but our swap space is not encrypted yet, then we need to set up an encrypted swap space manually. This can be done in two ways:
Either ways, it does not matter what kind of block device we are going to use respectively is already in use by the swap space right now — a separate HDD, RAID array, partition from some HDD already in use, LV, etc.
For both cases we need to identify the storage space i.e. its
device path like for example
Putting the encryption layer onto the block device earmarked to hold
the swap space is the same procedure for both cases i.e. the one
already shown above. Once this is done the only thing left to do is
automatize things i.e. make entries (respectively alter the old
What I showed above should be avoided if anyhow possible since it is a tedious and ever repeating task. Instead we want to just provide the password and not further intact with the computer during the booting phase. This sections shows how one might speed up things when using block-layer encryption.
I use GNOME (GNU Network Object Model Environment) so I have
sa@pc1:~$ dpl gnome-volume* | grep ^ii ii gnome-volume-manager 2.17.0-2 GNOME daemon to auto-mount and manage media devices sa@pc1:~$
After I entered my password (I always do a copy paste from a password manager application or an encrypted file containing my passwords and other sensitive information),
,----[ cat ~/.sec/README ] | Usage: | | - `gpg --symmetric <file>' to encrypt a file and | - `gpg --decrypt <file>.gpg' to decrypt it `----
the HDD got mounted as
sa@pc1:~$ ls -l /dev/mapper/ total 0 brw-rw---- 1 root disk 253, 0 2007-07-05 11:15 alan crw-rw---- 1 root root 10, 63 2007-07-05 11:02 control brw-rw---- 1 root disk 253, 1 2007-07-06 22:33 luks_crypto_eeeeedc3-6627-4d28-bbb4-d7f31924ba38 sa@pc1:~$ ls -1 /media/ | grep ^disk disk disk-1 sa@pc1:~$ ls -l /media/disk-1 total 0 drwxr-xr-x 3 sa sa 29 2006-07-11 00:33 xxxxxxxxxxxxxxxxxx drwxr-xr-x 4 sa sa 29 2007-05-28 14:21 xxxxxxxxxxxxxxxxxx drwxr-xr-x 8 sa sa 29 2006-05-22 07:39 xxxxxxxxxxxxxxxxxx drwxr-xr-x 3 sa sa 29 2006-11-22 05:02 xxxxxxxxxxxxxxxxxx drwxr-xr-x 4 sa sa 30 2007-05-29 03:28 xxxxxxxxxxxxxxxxxx sa@pc1:~$
I can now access all data as usual as the screendump above shows
(remember what I said about that dm-crypt is transparent
encryption). Note that the content of
There are a few CLI tools and files that can be used to automatize things e.g. automatically mount encrypted block devices and prompt the user for their passwords while doing so.
What is also important is not just what each of them does but how they
interact with each another. The reader might take a look at the man
This section is used as a collection for information not directly related to dm-crypt but nevertheless has relations to block-layer encryption.
1. A geek is an individual who is fascinated by knowledge and imagination, usually electronic or virtual in nature. (Wikipedia)
2. This term is misinterpreted almost all the time.
3. A group of people, which can be as small as one person.
4. For all of them, may they act as a matter of insanity or well though out plans based on common logic it doesn't matter for the one being the chosen victim.
5. Don't get me wrong here. I think America (same goes for their allies) is a great country (in fact I love it a lot) with great people living there but... Let me do a quote: Fighting fire with fire only gets you ashes! — Abigail van Buren (1918 - ) and another one: I like to believe that people in the long run are going to do more to promote peace than our governments. Indeed, I think that people want peace so much that one of these days governments had better get out of the way and let them have it. — Dwight D. Eisenhower
6. I don't know whether to fear a bunch of ragtag freedom fighters from another country, or my own government's 1984-style policies. We are waging a war on terror and we don't even know who the fuck the real enemy is. (The Urban Dictionary)
7. At this point information still is a secret. People, businesses etc. are willing to pay in order to know secrets. This is the moment where even children should sense the value of being in power of who knows what at what time to what conditions.
8. The data could be read by a criminal but not be interpreted/decrypted. So, loss of a computers hard disk that holds encrypted data does not cause harm even if lost to criminals — it is simply worthless for anybody without the key to decrypt the data stored on the disk. That, of course goes for any other device as well: CD-ROM, iPod, DVD, mobile phone, USB stick, floppy Disk etc. In fact every device which is able to hold data can hold encrypted data.
9. Note, that chaos does not equal anarchy — most people have a completely wrong understanding of the term anarchy. Anarchy is not the absence of social order within a society but only the absence of some sort of governmental powers that enforces that order. In fact, anarchy would be preferable to democracy since humans would live in peace and harmony without the need of powers that enforce that order, but that would in turn require a better human species. Since that is not the case, best we came up with until now is democracy (nowadays this is surely another democracy (better for rulers, worse for the people) than the old Greeks had back then...) — certainly not the best thing out there but as it seems the best working thing to keep folks from fighting each another on a daily basis since some ruling powers created an aggressive environment in a social, political and economical way. Do not raise your eybrowne but better get informed what press and media is telling you wrong since decades about the term anarchy and furthermore rethink democracy — what it is and what it probably should be.
10. It seems the human race cannot be without that rulers <—> people thingy. Some say what is best in this regards is not the best for the majority they rule but for the rulers themselves — not always is what is best for the rulers also the best for the people.
14. Determines if it is possible to do I/O (Input/Output) on a storage (i.e. VG in our case) while the VG is moved around, resized etc. (= online) or if I/O is not possible during that time (= offline).
15. The task of creating a partition. It is the very first thing one does. After partitioning, what follows is mostly the creation of a file system on top of the partition. After that the partition is mounted and can be used to store data.
16. The device-mapper within the linux kernel providing encryption for block devices.
17. LUKS is a standard describing encryption in conjunction with
dm-crypt but no actual tool to use. The tool which finally
provides the implementation of LUKS and can be practically used
18. A specialized device for use on a network. For example, Web servers, cache servers and file servers can be implemented as general-purpose computers with the appropriate software or as network appliances, which are computers dedicated to a single function and cannot do anything else. See server appliance, Internet appliance and Web cache. (The Free Computing Dictionary)
19. A hash can be used as key next to many other applications.
20. Of course no one would name it that way since that would be to
obvious — less suspicious would be
21. Note, that what might look as a random thing can be well described with mathematics e.g. stochastic theory and probabilistic theory and therefore it can be said that even if used on a daily basis by humans it is believed that true randomness only exists with quantum physics i.e. if for example random boy gets married to random girl after the random event of love at first sight, that is for sure no randomness but can be well described with stochastic theory and the like.
23. mapping - a function such that for every element of one set there is a unique element of another set. (The Free Dictionary) A modern hard drive comes with many spare sectors. When a sector is found to be bad by the firmware of a disk controller, the disk controller remaps the logical sector to a different physical sector. (Wikipedia)
24. For now we can be satisfied with the rough assumption of: ballooning factor = number of physical sectors onto the HDD.
28. The intention with block-layer encryption is not only to hide WHAT you have stored onto some storage media but also to hide THAT you have stored some particular data. In simple words, if you store a document/mp3/movie/etc. that you are not allowed to posses onto your storage media (HDD, USB stick, DVD, etc.), it can be proven (without the need to decrypt) that you stored that stuff. Denying you did not copy/download etc. this or that does not work — the simple fact that you posses it now is enough. Any document can be prepared with a redundant piece of code (a watermark), leaving intact the mp3/movie/.doc/PDF/etc. but revealing that you stored it even that you are using block-layer encryption. You have to use block-layer encryption with additional parameters like ESSIV (Encrypted Salt-Sector Initialization Vector) for example in order to be secure.
29. Unfortunately not all manufactures provide information to the public about their device to ID mapping thus the file is as good as the information a manufacturer provides.
30. Note that
31. However, this iPod is about four years old — today I would not buy a proprietary thing anymore because of the emerging FOSS (Free and Open Source Software) alternatives plus I think Apple sucks a bit since they sells their stuff completely overpriced ... but then that is another story, also known as Apple Hype.
32. HDD (Hard Disk Drive) I/O (Input/Output) is happening as usual from the point of view of any userspace application.
33. Opening in this regard means to unlock the device for subsequent en/decryption to/from the HDD (Hard Disk Drive) respectively any other storage media that has been equipped with dm-crypt.
34. This has to be the just created logical virtual block device