Annotation of wikisrc/guide/cgd.mdwn, revision 1.6

1.4       jdf         1: **Contents**
                      2: 
                      3: [[!toc levels=3]]
                      4: 
1.1       jdf         5: # The cryptographic device driver (CGD)
                      6: 
1.5       plunky      7: The [[!template id=man name="cgd" section="4"]] driver
1.3       jdf         8: provides functionality which allows you to use disks or partitions for encrypted
                      9: storage. After providing the appropriate key, the encrypted partition is
1.1       jdf        10: accessible using `cgd` pseudo-devices.
                     11: 
                     12: ## Overview
                     13: 
1.3       jdf        14: People often store sensitive information on their hard disks and are concerned
                     15: about this information falling into the wrong hands. This is particularly
                     16: relevant to users of laptops and other portable devices, or portable media,
1.1       jdf        17: which might be stolen or accidentally misplaced.
                     18: 
                     19: ### Why use disk encryption?
                     20: 
1.3       jdf        21: File-oriented encryption tools like GnuPG are great for encrypting individual
                     22: files, which can then be sent across untrusted networks as well as stored
                     23: encrypted on disk. But sometimes they can be inconvenient, because the file must
                     24: be decrypted each time it is to be used; this is especially cumbersome when you
                     25: have a large collection of files to protect. Any time a security tool is
                     26: cumbersome to use, there's a chance you'll forget to use it properly, leaving
1.1       jdf        27: the files unprotected for the sake of convenience.
                     28: 
1.3       jdf        29: Worse, readable copies of the encrypted contents might still exist on the hard
                     30: disk. Even if you overwrite these files (using `rm -P`) before unlinking them,
                     31: your application software might make temporary copies you don't know about, or
                     32: have been paged to swapspace - and even your hard disk might have silently
1.1       jdf        33: remapped failing sectors with data still in them.
                     34: 
1.3       jdf        35: The solution is to simply never write the information unencrypted to the hard
                     36: disk. Rather than taking a file-oriented approach to encryption, consider a
                     37: block-oriented approach - a virtual hard disk, that looks just like a normal
                     38: hard disk with normal filesystems, but which encrypts and decrypts each block on
1.1       jdf        39: the way to and from the real disk.
                     40: 
                     41: ### Logical Disk Drivers
                     42: 
1.3       jdf        43: The `cgd` device looks and behaves to the rest of the operating system like any
                     44: other disk driver. Rather than driving real hardware directly, it provides a
                     45: logical function layered on top of another block device. It has a special
                     46: configuration program,
1.5       plunky     47: [[!template id=man name="cgdconfig" section="8"]],
1.3       jdf        48: to create and configure a `cgd` device and point it at the underlying disk
1.1       jdf        49: device that will hold the encrypted data.
                     50: 
1.3       jdf        51: NetBSD includes several other similar logical block devices, each of which
                     52: provides some other function where `cgd` provides encryption. You can stack
                     53: several of these logical block devices together: you can make an encrypted
1.1       jdf        54: `raid` to protect your encrypted data against hard disk failure as well.
                     55: 
1.3       jdf        56: Once you have created a `cgd` disk, you can use
1.5       plunky     57: [[!template id=man name="disklabel" section="8"]]
1.3       jdf        58: to divide it up into partitions,
1.5       plunky     59: [[!template id=man name="swapctl" section="8"]] to
1.3       jdf        60: enable swapping to those partitions or
1.5       plunky     61: [[!template id=man name="newfs" section="8"]] to make
1.3       jdf        62: filesystems, then `mount` and use those filesystems, just like any other new
1.1       jdf        63: disk.
                     64: 
                     65: ## Components of the Crypto-Graphic Disk system
                     66: 
1.3       jdf        67: A number of components and tools work together to make the `cgd` system
1.1       jdf        68: effective.
                     69: 
                     70: ### Kernel driver pseudo-device
                     71: 
1.3       jdf        72: To use `cgd` you need a kernel with support for the `cgd` pseudo-device. Make
1.6     ! nia        73: sure the module is loaded:
1.1       jdf        74: 
1.6     ! nia        75:     modload cgd
1.1       jdf        76: 
1.6     ! nia        77: If the cgd driver was not already present/loaded, add `cgd` to `/etc/modules.conf`.
1.1       jdf        78: 
                     79: ### Ciphers
                     80: 
                     81: The `cgd` driver provides the following encryption algorithms:
                     82: 
1.3       jdf        83:  * `aes-cbc` -- AES (Rijndael). AES uses a 128 bit blocksize and accepts 128,
1.1       jdf        84:    192 or 256 bit keys.
                     85: 
                     86:  * `blowfish-cbc` -- Blowfish uses a 64 bit blocksize and accepts 128 bit keys
                     87: 
1.3       jdf        88:  * `3des-cbc` -- Triple DES uses a 64 bit blocksize and accepts 192 bit keys
1.1       jdf        89:    (only 168 bits are actually used for encryption)
                     90: 
1.3       jdf        91: All three ciphers are used in [CBC (Cipher Block
1.1       jdf        92: Chaining)](http://en.wikipedia.org/wiki/Cipher_block_chaining)
1.3       jdf        93: mode. This means each block is XORed with the previous encrypted block before
                     94: encryption. This reduces the risk that a pattern can be found, which can be used
1.1       jdf        95: to break the encryption.
                     96: 
                     97: ### Verification Methods
                     98: 
1.3       jdf        99: Another aspect of `cgd` that needs some attention are the verification methods
                    100: `cgdconfig` provides. These verification methods are used to verify the
1.1       jdf       101: passphrase is correct. The following verification methods are available:
                    102: 
1.3       jdf       103:  * `none` -- no verification is performed. This can be dangerous, because the
                    104:    key is not verified at all. When a wrong key is entered, `cgdconfig`
                    105:    configures the `cgd` device as normal, but data which was available on the
                    106:    volume will be destroyed (decrypting blocks with a wrong key will result in
                    107:    random data, which will result in a regeneration of the disklabel with the
1.1       jdf       108:    current key).
                    109: 
1.3       jdf       110:  * `disklabel` -- `cgdconfig` scans for a valid disklabel. If a valid disklabel
1.1       jdf       111:    is found with the key that is provided authentication will succeed.
                    112: 
1.3       jdf       113:  * `ffs` -- `cgdconfig` scans for a valid FFS file system. If a valid FFS file
1.1       jdf       114:    system is found with the key that is provided authentication will succeed.
                    115: 
                    116: ## Example: encrypting your disk
                    117: 
1.3       jdf       118: This section works through a step-by-step example of converting an existing
1.1       jdf       119: system to use `cgd`, performing the following actions:
                    120: 
                    121:  1. Preparing the disk and partitions
                    122:  2. Scrub off all data
                    123:  3. Create the cgd
                    124:  4. Adjust config-files
                    125:  5. Restoring your backed-up files to the encrypted disk
                    126: 
                    127: ### Preparing the disk
                    128: 
1.3       jdf       129: First, decide which filesystems you want to move to an encrypted device. You're
                    130: going to need to leave at least the small root (`/`) filesystem unencrypted, in
                    131: order to load the kernel and run `init`, `cgdconfig` and the `rc.d` scripts that
                    132: configure your `cgd`. In this example, we'll encrypt everything except the root
1.1       jdf       133: (`/`) filesystem.
                    134: 
1.3       jdf       135: We are going to delete and re-make partitions and filesystems, and will require
                    136: a backup to restore the data. So make sure you have a current, reliable backup
                    137: stored on a different disk or machine. Do your backup in single-user mode, with
                    138: the filesystems unmounted, to ensure you get a clean
1.5       plunky    139: [[!template id=man name="dump" section="8"]]. Make sure you
1.3       jdf       140: back up the disklabel of your hard disk as well, so you have a record of the
1.1       jdf       141: partition layout before you started.
                    142: 
1.3       jdf       143: With the system at single user, `/` mounted read-write and everything else
                    144: unmounted, use
1.5       plunky    145: [[!template id=man name="disklabel" section="8"]]
1.1       jdf       146: to delete all the data partitions you want to move into `cgd`.
                    147: 
1.3       jdf       148: Then make a single new partition in all the space you just freed up, say,
                    149: `wd0e`. Set the partition type for this partition to `cgd` Though it doesn't
                    150: really matter what it is, it will help remind you that it's not a normal
1.1       jdf       151: filesystem later. When finished, label the disk to save the new partition table.
                    152: 
                    153: ### Scrubbing the disk
                    154: 
1.3       jdf       155: We have removed the partition table information, but the existing filesystems
                    156: and data are still on disk. Even after we make a `cgd` device, create
                    157: filesystems, and restore our data, some of these disk blocks might not yet be
                    158: overwritten and still contain our data in plaintext. This is especially likely
                    159: if the filesystems are mostly empty. We want to scrub the disk before we go
1.1       jdf       160: further.
                    161: 
1.3       jdf       162: We could use
1.5       plunky    163: [[!template id=man name="dd" section="1"]]
1.3       jdf       164: to copy `/dev/zero` over the new `wd0e` partition, but this will leave our disk
                    165: full of zeros, except where we've written encrypted data later. We might not
                    166: want to give an attacker any clues about which blocks contain real data, and
                    167: which are free space, so we want to write "noise" into all the disk blocks. So
1.1       jdf       168: we'll create a temporary `cgd`, configured with a random, unknown key.
                    169: 
                    170: First, we configure a `cgd` to use a random key:
                    171: 
1.3       jdf       172:     # cgdconfig -s cgd0 /dev/wd0e aes-cbc 128 < /dev/urandom
1.1       jdf       173: 
1.3       jdf       174: Now we can write zeros into the raw partition of our `cgd` (`/dev/rcgd0d` on
1.1       jdf       175: NetBSD/i386, `/dev/rcgd0c` on most other platforms):
                    176: 
                    177:     # dd if=/dev/zero of=/dev/rcgd0d bs=32k
                    178: 
1.3       jdf       179: The encrypted zeros will look like random data on disk. This might take a while
1.1       jdf       180: if you have a large disk. Once finished, unconfigure the random-key `cgd`:
                    181: 
                    182:     # cgdconfig -u cgd0
                    183: 
                    184: ### Creating the `cgd`
                    185: 
1.3       jdf       186: The
1.5       plunky    187: [[!template id=man name="cgdconfig" section="8"]]
1.3       jdf       188: program, which manipulates `cgd` devices, uses parameters files to store such
                    189: information as the encryption type, key length, and a random password salt for
                    190: each `cgd`. These files are very important, and need to be kept safe - without
1.1       jdf       191: them, you will not be able to decrypt the data!
                    192: 
1.3       jdf       193: We'll generate a parameters file and write it into the default location (make
1.1       jdf       194: sure the directory `/etc/cgd` exists and is mode 700):
                    195: 
                    196:     # cgdconfig -g -V disklabel -o /etc/cgd/wd0e aes-cbc 256
                    197: 
1.3       jdf       198: This creates a parameters file `/etc/cgd/wd0e` describing a `cgd` using the
                    199: `aes-cbc` cipher method, a key verification method of `disklabel`, and a key
1.1       jdf       200: length of `256` bits. It will look something like this:
                    201: 
                    202:     algorithm aes-cbc;
                    203:     iv-method encblkno;
                    204:     keylength 256;
                    205:     verify_method disklabel;
                    206:     keygen pkcs5_pbkdf2/sha1 {
                    207:             iterations 6275;
                    208:             salt AAAAgHTg/jKCd2ZJiOSGrgnadGw=;
                    209:     };
                    210: 
                    211: *Note*: Remember, you'll want to save this file somewhere safe later.
                    212: 
1.3       jdf       213: *Tip*: When creating the parameters file, `cgdconfig` reads from `/dev/random`
                    214: to create the password salt. This read may block if there is not enough
                    215: collected entropy in the random pool. This is unlikely, especially if you just
                    216: finished overwriting the disk as in the previous step, but if it happens you can
                    217: press keys on the console and/or move your mouse until the `rnd` device gathers
1.1       jdf       218: enough entropy.
                    219: 
1.3       jdf       220: Now it's time to create our `cgd`, for which we'll need a passphrase. This
                    221: passphrase needs to be entered every time the `cgd` is opened, which is usually
                    222: at each reboot. The encryption key is derived from this passphrase and the salt.
1.1       jdf       223: Make sure you choose something you won't forget, and others won't guess.
                    224: 
1.3       jdf       225: The first time we configure the `cgd`, there is no valid disklabel on the
                    226: logical device, so the validation mechanism we want to use later won't work. We
1.1       jdf       227: override it this one time:
                    228: 
                    229:     # cgdconfig -V re-enter cgd0 /dev/wd0e
                    230: 
1.3       jdf       231: This will prompt twice for a matching passphrase, just in case you make a typo,
                    232: which would otherwise leave you with a `cgd` encrypted with a passphrase that's
1.1       jdf       233: different to what you expected.
                    234: 
1.3       jdf       235: Now that we have a new `cgd`, we need to partition it and create filesystems.
                    236: Recreate your previous partitions with all the same sizes, with the same letter
1.1       jdf       237: names.
                    238: 
1.3       jdf       239: *Tip*: Remember to use the `disklabel -I` argument, because you're creating an
1.1       jdf       240: initial label for a new disk.
                    241: 
1.3       jdf       242: *Note*: Although you want the sizes of your new partitions to be the same as the
                    243: old, unencrypted ones, the offsets will be different because they're starting at
1.1       jdf       244: the beginning of this virtual disk.
                    245: 
1.3       jdf       246: Then, use
1.5       plunky    247: [[!template id=man name="newfs" section="8"]] to
1.3       jdf       248: create filesystems on all the relevant partitions. This time your partitions
1.1       jdf       249: will reflect the `cgd` disk names, for example:
                    250: 
                    251:     # newfs /dev/rcgd0h
                    252: 
                    253: ### Modifying configuration files
                    254: 
1.3       jdf       255: We've moved several filesystems to another (logical) disk, and we need to update
                    256: `/etc/fstab` accordingly. Each partition will have the same letter (in this
                    257: example), but will be on `cgd0` rather than `wd0`. So you'll have `/etc/fstab`
1.1       jdf       258: entries something like this:
                    259: 
                    260:     /dev/wd0a   /     ffs     rw    1 1
                    261:     /dev/cgd0b  none  swap    sw            0 0
                    262:     /dev/cgd0b  /tmp  mfs     rw,-s=132m    0 0
                    263:     /dev/cgd0e  /var  ffs     rw            1 2
                    264:     /dev/cgd0f  /usr  ffs     rw            1 2
                    265:     /dev/cgd0h  /home ffs     rw            1 2
                    266: 
1.3       jdf       267: *Note*: `/tmp` should be a separate filesystem, either `mfs` or `ffs`, inside
                    268: the `cgd`, so that your temporary files are not stored in plain text in the `/`
1.1       jdf       269: filesystem.
                    270: 
1.3       jdf       271: Each time you reboot, you're going to need your `cgd` configured early, before
1.5       plunky    272: [[!template id=man name="fsck" section="8"]] runs and
1.1       jdf       273: filesystems are mounted.
                    274: 
                    275: Put the following line in `/etc/cgd/cgd.conf`:
                    276: 
                    277:     cgd0    /dev/wd0e
                    278: 
                    279: This will use `/etc/cgd/wd0e` as config file for `cgd0`.
                    280: 
                    281: To finally enable cgd on each boot, put the following line into `/etc/rc.conf`:
                    282: 
                    283:     cgd=YES
                    284: 
1.3       jdf       285: You should now be prompted for `/dev/cgd0`'s passphrase whenever `/etc/rc`
1.1       jdf       286: starts.
                    287: 
                    288: ### Restoring data
                    289: 
1.3       jdf       290: Next, mount your new filesystems, and
1.5       plunky    291: [[!template id=man name="restore" section="8"]] your
1.3       jdf       292: data into them. It often helps to have `/tmp` mounted properly first, as
                    293: `restore` can use a fair amount of temporary space when extracting a large
1.1       jdf       294: dumpfile.
                    295: 
1.3       jdf       296: To test your changes to the boot configuration, umount the filesystems and
                    297: unconfigure the `cgd`, so when you exit the single-user shell, *rc* will run
                    298: like on a clean boot, prompting you for the passphrase and mounting your
                    299: filesystems correctly. Now you can bring the system up to multi-user, and make
1.1       jdf       300: sure everything works as before.
                    301: 
                    302: ## Example: encrypted CDs/DVDs
                    303: 
                    304: ### Introduction
                    305: 
1.3       jdf       306: This section explains how to create and use encrypted CDs/DVDs with NetBSD (all
                    307: I say about CDs here does also apply to DVDs). I assume that you have basic
                    308: knowledge of cgd(4), so I will not explain what cgd is or what's inside it in
                    309: detail. The same applies to vnd(4). One can make use of encrypted CDs after
                    310: reading this howto, but for more detailed information about different cgd
1.1       jdf       311: configuration options, please read the previous parts or the manpages.
                    312: 
                    313: ### Creating an encrypted CD/DVD
                    314: 
1.3       jdf       315: cgd(4) provides highly secure encryption of whole partitions or disks.
                    316: Unfortunately, creating "normal" CDs is not disklabeling something and running
                    317: newfs on it. Neither can you just put a CDR into the drive, configure cgd and
                    318: assume it to write encrypted data when syncing. Standard CDs contain at least an
                    319: ISO-9660 filesystem created with mkisofs(8) from the
                    320: [`sysutils/cdrtools`](http://ftp.NetBSD.org/pub/pkgsrc/current/pkgsrc/sysutils/cdrtools/README.html)
1.1       jdf       321: package. ISO images must *not* contain disklabels or cgd partitions.
                    322: 
1.3       jdf       323: But of course CD reader/writer hardware doesn't care about filesystems at all.
                    324: You can write raw data to the CD if you like - or an encrypted FFS filesystem,
                    325: which is what we'll do here. But be warned, there is NO way to read this CD with
1.1       jdf       326: any OS except NetBSD - not even other BSDs due to the lack of cgd.
                    327: 
                    328: The basic steps when creating an encrypted CD are:
                    329: 
                    330:  * Create an (empty) imagefile
                    331:  * Register it as a virtual disk using vnd(4)
                    332:  * Configure cgd inside the vnd disk
                    333:  * Copy content to the cgd
                    334:  * Unconfigure all (flush!)
                    335:  * Write the image on a CD
                    336: 
1.3       jdf       337: The first step when creating an encrypted CD is to create a single image file
                    338: with dd. The image may not grow, so make it large enough to allow all CD content
                    339: to fit into. Note that the whole image gets written to the CD later, so creating
                    340: a 700 MB image for 100 MB content will still require a 700 MB write operation to
                    341: the CD. Some info on DVDs here: DVDs are only 4.7 GB in marketing language.
                    342: 4.7GB = 4.7 x 1024 x 1024 x 1024 = 5046586573 bytes. In fact, a DVD can only
                    343: approximately hold 4.7 x 1000 x 1000 x 1000 = 4700000000 bytes, which is about
                    344: 4482 MB or about 4.37 GB. Keep this in mind when creating DVD images. Don't
1.1       jdf       345: worry for CDs, they hold "real" 700 MB (734003200 Bytes).
                    346: 
                    347: Invoke all following commands as root!
                    348: 
                    349: For a CD:
                    350: 
                    351:     # dd if=/dev/zero of=image.img bs=1m count=700
                    352: 
                    353: or, for a DVD:
                    354: 
                    355:     # dd if=/dev/zero of=image.img bs=1m count=4482
                    356: 
1.3       jdf       357: Now configure a
1.5       plunky    358: [[!template id=man name="vnd" section="4"]]-pseudo
1.1       jdf       359: disk with the image:
                    360: 
                    361:     # vnconfig vnd0 image.img
                    362: 
1.3       jdf       363: In order to use cgd, a so-called parameter file, describing encryption
                    364: parameters and a containing "password salt" must be generated. We'll call it
                    365: `/etc/cgd/image` here. You can use one parameter file for several encrypted
                    366: partitions (I use one different file for each host and a shared file `image` for
1.1       jdf       367: all removable media, but that's up to you).
                    368: 
1.3       jdf       369: I'll use AES-CBC with a keylength of 256 bits. Refer to
1.5       plunky    370: [[!template id=man name="cgd" section="4"]] and
                    371: [[!template id=man name="cgdconfig" section="8"]]
1.1       jdf       372: for details and alternatives.
                    373: 
1.3       jdf       374: The following command will create the parameter file as `/etc/cgd/image`. *YOU
                    375: DO NOT WANT TO INVOKE THE FOLLOWING COMMAND AGAIN* after you burnt any CD, since
                    376: a recreated parameter file is a lost parameter file and you'll never access your
                    377: encrypted CD again (the "salt" this file contains will differ among each call).
                    378: Consider this file being *HOLY, BACKUP IT* and *BACKUP IT AGAIN!* Use switch -V
                    379: to specify verification method "disklabel" for the CD (cgd cannot detect whether
1.1       jdf       380: you entered a valid password for the CD later when mounting it otherwise).
                    381: 
                    382:     # cgdconfig -g -V disklabel aes-cbc 256 > /etc/cgd/image
                    383: 
1.3       jdf       384: Now it's time to configure a cgd for our vnd drive. (Replace slice `d` with `c`
1.1       jdf       385: for all platforms that use `c` as the whole disk (where
1.3       jdf       386: `sysctl kern.rawpartition` prints `2`, not `3`); if you're on i386 or amd64, `d`
1.1       jdf       387: is OK for you):
                    388: 
                    389:     # cgdconfig -V re-enter cgd1 /dev/vnd0d /etc/cgd/image
                    390: 
1.3       jdf       391: The `-V re-enter` option is necessary as long as the cgd doesn't have a
                    392: disklabel yet so we can access and configure it. This switch asks for a password
1.1       jdf       393: twice and uses it for encryption.
                    394: 
1.3       jdf       395: Now it's time to create a disklabel inside the cgd. The defaults of the label
1.1       jdf       396: are ok, so invoking disklabel with
                    397: 
                    398:     # disklabel -e -I cgd1
                    399: 
                    400: and leaving vi with `:wq` immediately will do.
                    401: 
                    402: Let's create a filesystem on the cgd, and finally mount it somewhere:
                    403: 
                    404:     # newfs /dev/rcgd1a
                    405:     # mount /dev/cgd1a /mnt
                    406: 
1.3       jdf       407: The cgd is alive! Now fill `/mnt` with content. When finished, reverse the
1.1       jdf       408: configuration process. The steps are:
                    409: 
                    410: 1.  Unmounting the cgd1a:
                    411: 
                    412:         # umount /mnt
                    413: 
                    414: 2.  Unconfiguring the cgd:
                    415: 
                    416:         # cgdconfig -u cgd1
                    417: 
                    418: 3.  Unconfiguring the vnd:
                    419: 
                    420:         # vnconfig -u vnd0
                    421: 
                    422: 
1.3       jdf       423: The following commands are examples to burn the images on CD or DVD. Please
                    424: adjust the `dev=` for cdrecord or the `/dev/rcd0d` for growisofs. Note the
                    425: `r` on the `rcd0d` *is* necessary with NetBSD. Growisofs is available in the
                    426: [`sysutils/dvd+rw-tools`](http://ftp.NetBSD.org/pub/pkgsrc/current/pkgsrc/sysutils/dvd+rw-tools/README.html)
                    427: package. Again, use `c` instead of `d` if this is the raw partition on your
1.1       jdf       428: platform.
                    429: 
                    430: Finally, write the image file to a CD:
                    431: 
                    432:     # cdrecord dev=/dev/rcd0d -v image.img
                    433: 
                    434: ...or to a DVD:
                    435: 
                    436:     # growisofs -dvd-compat -Z /dev/rcd0d=image.img
                    437: 
                    438: Congratulations! You've just created a really secure CD!
                    439: 
                    440: ### Using an encrypted CD/DVD
                    441: 
1.3       jdf       442: After creating an encrypted CD as described above, we're not done yet - what
                    443: about mounting it again? One might guess, configuring the cgd on `/dev/cd0d` is
1.1       jdf       444: enough - no, it is not.
                    445: 
1.3       jdf       446: NetBSD cannot access FFS file systems on media that is not 512 bytes/sector
                    447: format. It doesn't matter that the cgd on the CD is, since the CD's disklabel
1.1       jdf       448: the cgd resides in has 2048 bytes/sector.
                    449: 
1.3       jdf       450: But the CD driver cd(4) is smart enough to grant write access to the
                    451: (emulated) disklabel on the CD. So before configuring the cgd, let's have a look
1.1       jdf       452: at the disklabel and modify it a bit:
                    453: 
                    454:     # disklabel -e cd0
                    455:     # /dev/rcd0d:
                    456:     type: ATAPI
                    457:     disk: mydisc
                    458:     label: fictitious
                    459:     flags: removable
                    460:     bytes/sector: 2048    # -- Change to 512 (= orig / 4)
                    461:     sectors/track: 100    # -- Change to 400 (= orig * 4)
                    462:     tracks/cylinder: 1
                    463:     sectors/cylinder: 100 # -- Change to 400 (= orig * 4)
                    464:     cylinders: 164
                    465:     total sectors: 16386  # -- Change to value of slice "d" (=65544)
                    466:     rpm: 300
                    467:     interleave: 1
                    468:     trackskew: 0
                    469:     cylinderskew: 0
                    470:     headswitch: 0           # microseconds
                    471:     track-to-track seek: 0  # microseconds
                    472:     drivedata: 0
                    473:     
                    474:     4 partitions:
                    475:     #     size  offset  fstype [fsize bsize cpg/sgs]
                    476:      a:   65544   0     4.2BSD  0     0     0  # (Cyl. 0 - 655+)
                    477:      d:   65544   0     ISO9660 0     0        # (Cyl. 0 - 655+)
                    478: 
                    479: Now as the disklabel is in 512 b/s format, accessing the CD is as easy as:
                    480: 
                    481:     # cgdconfig cgd1 /dev/cd0d /etc/cgd/image
                    482:     # mount -o ro /dev/cgd1a /mnt
                    483: 
1.3       jdf       484: Note that the cgd *MUST* be mounted read-only or you'll get illegal command
                    485: errors from the cd(4) driver which can in some cases make even mounting a
1.1       jdf       486: CD-based cgd impossible!
                    487: 
                    488: Now we're done! Enjoy your secure CD!
                    489: 
                    490:     # ls /mnt
                    491: 
                    492: Remember you have to reverse all steps to remove the CD:
                    493: 
                    494:     # umount /mnt
                    495:     # cgdconfig -u cgd1
                    496:     # eject cd0
                    497: 
                    498: ## Suggestions and Warnings
                    499: 
1.3       jdf       500: You now have your filesystems encrypted within a `cgd`. When your machine is
                    501: shut down, the data is protected, and can't be decrypted without the passphrase.
                    502: However, there are still some dangers you should be aware of, and more you can
                    503: do with `cgd`. This section documents several further suggestions and warnings
1.1       jdf       504:        that will help you use `cgd` effectively.
                    505: 
1.3       jdf       506:  * Use multiple `cgd`'s for different kinds of data, one mounted all the time
1.1       jdf       507:    and others mounted only when needed.
                    508: 
1.3       jdf       509:  * Use a `cgd` configured on top of a `vnd` made from a file on a remote network
                    510:    fileserver (NFS, SMBFS, CODA, etc) to safely store private data on a shared
                    511:    system. This is similar to the procedure for using encrypted CDs and DVDs
1.1       jdf       512:    described in [[Example: encrypted CDs/DVDs|guide/cgd#cryptocds]].
                    513: 
                    514: ### Using a random-key cgd for swap
                    515: 
1.3       jdf       516: You may want to use a dedicated random-key `cgd` for swap space, regenerating
                    517: the key each reboot. The advantage of this is that once your machine is
                    518: rebooted, any sensitive program memory contents that may have been paged out are
1.1       jdf       519: permanently unrecoverable, because the decryption key is never known to you.
                    520: 
1.3       jdf       521: We created a temporary `cgd` with a random key when scrubbing the disk in the
                    522: example above, using a shorthand `cgdconfig -s` invocation to avoid creating a
1.1       jdf       523: parameters file.
                    524: 
1.3       jdf       525: The `cgdconfig` params file includes a *randomkey* keygen method. This is more
                    526: appropriate for *permanent* random-key configurations, and facilitates the easy
1.1       jdf       527: automatic configuration of these volumes at boot time.
                    528: 
1.3       jdf       529: For example, if you wanted to convert your existing `/dev/wd0b` partition to a
                    530: dedicated random-key cgd1, use the following command to generate
1.1       jdf       531: `/etc/cgd/wd0b`:
                    532: 
                    533:     # cgdconfig -g -o /etc/cgd/wd0b -V none -k randomkey blowfish-cbc
                    534: 
1.3       jdf       535: When using the randomkey keygen method, only verification method `none` can be
                    536: used, because the contents of the new `cgd` are effectively random each time
                    537: (the previous data decrypted with a random key). Likewise, the new disk will not
                    538: have a valid label or partitions, and `swapctl` will complain about
1.1       jdf       539: configuring swap devices not marked as such in a disklabel.
                    540: 
1.3       jdf       541: In order to automate the process of labeling the disk, prepare an appropriate
                    542: disklabel and save it to a file, for example `/etc/cgd/wd0b.disklabel`. Please
                    543: refer to
1.5       plunky    544: [[!template id=man name="disklabel" section="8"]]
1.1       jdf       545: for information about how to use `disklabel` to set up a swap partition.
                    546: 
1.3       jdf       547: On each reboot, to restore this saved label to the new `cgd`, create the
1.1       jdf       548: `/etc/rc.conf.d/cgd` file as below:
                    549: 
                    550:     swap_device="cgd1"
                    551:     swap_disklabel="/etc/cgd/wd0b.disklabel"
                    552:     start_postcmd="cgd_swap"
                    553:     
                    554:     cgd_swap()
                    555:     {
                    556:         if [ -f $swap_disklabel ]; then
                    557:             disklabel -R -r $swap_device $swap_disklabel
                    558:         fi
                    559:     }
                    560: 
1.3       jdf       561: The same technique could be extended to encompass using `newfs` to re-create
1.1       jdf       562: an `ffs` filesystem for `/tmp` if you didn't want to use `mfs`.
                    563: 
                    564: ### Warnings
                    565: 
1.3       jdf       566: Prevent cryptographic disasters by making sure you can always recover your
                    567: passphrase and parameters file. Protect the parameters file from disclosure,
                    568: perhaps by storing it on removable media as above, because the salt it contains
1.1       jdf       569: helps protect against dictionary attacks on the passphrase.
                    570: 
1.3       jdf       571: Keeping the data encrypted on your disk is all very well, but what about other
                    572: copies? You already have at least one other such copy (the backup we used during
                    573: this setup), and it's not encrypted. Piping `dump` through file-based
                    574: encryption tools like `gpg` can be one way of addressing this issue, but make
                    575: sure you have all the keys and tools you need to decrypt it to `restore` after
1.1       jdf       576: a disaster.
                    577: 
1.3       jdf       578: Like any form of software encryption, the `cgd` key stays in kernel memory while
                    579: the device is configured, and may be accessible to privileged programs and
                    580: users, such as `/dev/kmem` grovellers. Taking other system security steps, such
1.1       jdf       581: as running with elevated securelevel, is highly recommended.
                    582: 
1.3       jdf       583: Once the `cgd` volumes are mounted as normal filesystems, their contents are
                    584: accessible like any other file. Take care of file permissions and ensure your
1.1       jdf       585: running system is protected against application and network security attack.
                    586: 
1.3       jdf       587: Avoid using suspend/resume, especially for laptops with a BIOS suspend-to-disk
                    588: function. If an attacker can resume your laptop with the key still in memory, or
                    589: read it from the suspend-to-disk memory image on the hard disk later, the whole
1.1       jdf       590: point of using `cgd` is lost.
                    591: 
                    592: ## Further Reading
                    593: 
                    594: The following resources contain more information on CGD:
                    595: 
                    596: ### Bibliography
                    597: 
1.2       jdf       598:  * [smackie-cgd]: *[NetBSD CGD Setup](http://www.bsdguides.org/guides/netbsd/misc/cgd_setup.php)*. Stuart Mackie.
                    599:  * [nycbug-cgd]: *[I want my cgd](http://genoverly.com/articles/view/5/) aka: I want an encrypted pseudo-device on my laptop*.
                    600:  * [elric-cgd]: *The original paper on [The CryptoGraphic Disk Driver](http://www.imrryr.org/~elric/cgd/cgd.pdf)*. Roland Dowdeswell and John Ioannidis.
                    601:  * [biancuzzi-cgd]: *[Inside NetBSD's CGD](http://onlamp.com/pub/a/bsd/2005/12/21/netbsd_cgd.html) - an interview with CGD creator Roland Dowdeswell*. Biancuzzi Federico.
                    602:  * [hubertf-cgd]: *[CryptoGraphicFile (CGF)](http://www.feyrer.de/NetBSD/blog.html/nb_20060823_2311.html), or how to keep sensitive data on your laptop*. Feyrer Hubert.
1.1       jdf       603: 

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