Annotation of wikisrc/guide/cgd.mdwn, revision 1.3

1.1       jdf         1: # The cryptographic device driver (CGD)
                      2: 
1.3     ! jdf         3: The [cgd(4)](http://netbsd.gw.com/cgi-bin/man-cgi?cgd+4+NetBSD-current) driver
        !             4: provides functionality which allows you to use disks or partitions for encrypted
        !             5: storage. After providing the appropriate key, the encrypted partition is
1.1       jdf         6: accessible using `cgd` pseudo-devices.
                      7: 
                      8: ## Overview
                      9: 
1.3     ! jdf        10: People often store sensitive information on their hard disks and are concerned
        !            11: about this information falling into the wrong hands. This is particularly
        !            12: relevant to users of laptops and other portable devices, or portable media,
1.1       jdf        13: which might be stolen or accidentally misplaced.
                     14: 
                     15: ### Why use disk encryption?
                     16: 
1.3     ! jdf        17: File-oriented encryption tools like GnuPG are great for encrypting individual
        !            18: files, which can then be sent across untrusted networks as well as stored
        !            19: encrypted on disk. But sometimes they can be inconvenient, because the file must
        !            20: be decrypted each time it is to be used; this is especially cumbersome when you
        !            21: have a large collection of files to protect. Any time a security tool is
        !            22: cumbersome to use, there's a chance you'll forget to use it properly, leaving
1.1       jdf        23: the files unprotected for the sake of convenience.
                     24: 
1.3     ! jdf        25: Worse, readable copies of the encrypted contents might still exist on the hard
        !            26: disk. Even if you overwrite these files (using `rm -P`) before unlinking them,
        !            27: your application software might make temporary copies you don't know about, or
        !            28: have been paged to swapspace - and even your hard disk might have silently
1.1       jdf        29: remapped failing sectors with data still in them.
                     30: 
1.3     ! jdf        31: The solution is to simply never write the information unencrypted to the hard
        !            32: disk. Rather than taking a file-oriented approach to encryption, consider a
        !            33: block-oriented approach - a virtual hard disk, that looks just like a normal
        !            34: hard disk with normal filesystems, but which encrypts and decrypts each block on
1.1       jdf        35: the way to and from the real disk.
                     36: 
                     37: ### Logical Disk Drivers
                     38: 
1.3     ! jdf        39: The `cgd` device looks and behaves to the rest of the operating system like any
        !            40: other disk driver. Rather than driving real hardware directly, it provides a
        !            41: logical function layered on top of another block device. It has a special
        !            42: configuration program,
        !            43: [cgdconfig(8)](http://netbsd.gw.com/cgi-bin/man-cgi?cgdconfig+8+NetBSD-current),
        !            44: to create and configure a `cgd` device and point it at the underlying disk
1.1       jdf        45: device that will hold the encrypted data.
                     46: 
1.3     ! jdf        47: NetBSD includes several other similar logical block devices, each of which
        !            48: provides some other function where `cgd` provides encryption. You can stack
        !            49: several of these logical block devices together: you can make an encrypted
1.1       jdf        50: `raid` to protect your encrypted data against hard disk failure as well.
                     51: 
1.3     ! jdf        52: Once you have created a `cgd` disk, you can use
        !            53: [disklabel(8)](http://netbsd.gw.com/cgi-bin/man-cgi?disklabel+8+NetBSD-current)
        !            54: to divide it up into partitions,
        !            55: [swapctl(8)](http://netbsd.gw.com/cgi-bin/man-cgi?swapctl+8+NetBSD-current) to
        !            56: enable swapping to those partitions or
        !            57: [newfs(8)](http://netbsd.gw.com/cgi-bin/man-cgi?newfs+8+NetBSD-current) to make
        !            58: filesystems, then `mount` and use those filesystems, just like any other new
1.1       jdf        59: disk.
                     60: 
                     61: ## Components of the Crypto-Graphic Disk system
                     62: 
1.3     ! jdf        63: A number of components and tools work together to make the `cgd` system
1.1       jdf        64: effective.
                     65: 
                     66: ### Kernel driver pseudo-device
                     67: 
1.3     ! jdf        68: To use `cgd` you need a kernel with support for the `cgd` pseudo-device. Make
1.1       jdf        69: sure the following line is in the kernel configuration file:
                     70: 
                     71:     pseudo-device   cgd     4       # cryptographic disk driver
                     72: 
1.3     ! jdf        73: The number specifies how many `cgd` devices may be configured at the same time.
        !            74: After configuring the `cgd` pseudo-device you can recompile the kernel and boot
1.1       jdf        75: it to enable `cgd` support.
                     76: 
                     77: ### Ciphers
                     78: 
                     79: The `cgd` driver provides the following encryption algorithms:
                     80: 
1.3     ! jdf        81:  * `aes-cbc` -- AES (Rijndael). AES uses a 128 bit blocksize and accepts 128,
1.1       jdf        82:    192 or 256 bit keys.
                     83: 
                     84:  * `blowfish-cbc` -- Blowfish uses a 64 bit blocksize and accepts 128 bit keys
                     85: 
1.3     ! jdf        86:  * `3des-cbc` -- Triple DES uses a 64 bit blocksize and accepts 192 bit keys
1.1       jdf        87:    (only 168 bits are actually used for encryption)
                     88: 
1.3     ! jdf        89: All three ciphers are used in [CBC (Cipher Block
1.1       jdf        90: Chaining)](http://en.wikipedia.org/wiki/Cipher_block_chaining)
1.3     ! jdf        91: mode. This means each block is XORed with the previous encrypted block before
        !            92: encryption. This reduces the risk that a pattern can be found, which can be used
1.1       jdf        93: to break the encryption.
                     94: 
                     95: ### Verification Methods
                     96: 
1.3     ! jdf        97: Another aspect of `cgd` that needs some attention are the verification methods
        !            98: `cgdconfig` provides. These verification methods are used to verify the
1.1       jdf        99: passphrase is correct. The following verification methods are available:
                    100: 
1.3     ! jdf       101:  * `none` -- no verification is performed. This can be dangerous, because the
        !           102:    key is not verified at all. When a wrong key is entered, `cgdconfig`
        !           103:    configures the `cgd` device as normal, but data which was available on the
        !           104:    volume will be destroyed (decrypting blocks with a wrong key will result in
        !           105:    random data, which will result in a regeneration of the disklabel with the
1.1       jdf       106:    current key).
                    107: 
1.3     ! jdf       108:  * `disklabel` -- `cgdconfig` scans for a valid disklabel. If a valid disklabel
1.1       jdf       109:    is found with the key that is provided authentication will succeed.
                    110: 
1.3     ! jdf       111:  * `ffs` -- `cgdconfig` scans for a valid FFS file system. If a valid FFS file
1.1       jdf       112:    system is found with the key that is provided authentication will succeed.
                    113: 
                    114: ## Example: encrypting your disk
                    115: 
1.3     ! jdf       116: This section works through a step-by-step example of converting an existing
1.1       jdf       117: system to use `cgd`, performing the following actions:
                    118: 
                    119:  1. Preparing the disk and partitions
                    120:  2. Scrub off all data
                    121:  3. Create the cgd
                    122:  4. Adjust config-files
                    123:  5. Restoring your backed-up files to the encrypted disk
                    124: 
                    125: ### Preparing the disk
                    126: 
1.3     ! jdf       127: First, decide which filesystems you want to move to an encrypted device. You're
        !           128: going to need to leave at least the small root (`/`) filesystem unencrypted, in
        !           129: order to load the kernel and run `init`, `cgdconfig` and the `rc.d` scripts that
        !           130: configure your `cgd`. In this example, we'll encrypt everything except the root
1.1       jdf       131: (`/`) filesystem.
                    132: 
1.3     ! jdf       133: We are going to delete and re-make partitions and filesystems, and will require
        !           134: a backup to restore the data. So make sure you have a current, reliable backup
        !           135: stored on a different disk or machine. Do your backup in single-user mode, with
        !           136: the filesystems unmounted, to ensure you get a clean
        !           137: [dump(8)](http://netbsd.gw.com/cgi-bin/man-cgi?dump+8+NetBSD-current). Make sure you
        !           138: back up the disklabel of your hard disk as well, so you have a record of the
1.1       jdf       139: partition layout before you started.
                    140: 
1.3     ! jdf       141: With the system at single user, `/` mounted read-write and everything else
        !           142: unmounted, use
1.1       jdf       143: [disklabel(8)](http://netbsd.gw.com/cgi-bin/man-cgi?disklabel+8+NetBSD-current)
                    144: to delete all the data partitions you want to move into `cgd`.
                    145: 
1.3     ! jdf       146: Then make a single new partition in all the space you just freed up, say,
        !           147: `wd0e`. Set the partition type for this partition to `cgd` Though it doesn't
        !           148: really matter what it is, it will help remind you that it's not a normal
1.1       jdf       149: filesystem later. When finished, label the disk to save the new partition table.
                    150: 
                    151: ### Scrubbing the disk
                    152: 
1.3     ! jdf       153: We have removed the partition table information, but the existing filesystems
        !           154: and data are still on disk. Even after we make a `cgd` device, create
        !           155: filesystems, and restore our data, some of these disk blocks might not yet be
        !           156: overwritten and still contain our data in plaintext. This is especially likely
        !           157: if the filesystems are mostly empty. We want to scrub the disk before we go
1.1       jdf       158: further.
                    159: 
1.3     ! jdf       160: We could use
1.1       jdf       161: [dd(1)](http://netbsd.gw.com/cgi-bin/man-cgi?dd+1+NetBSD-current)
1.3     ! jdf       162: to copy `/dev/zero` over the new `wd0e` partition, but this will leave our disk
        !           163: full of zeros, except where we've written encrypted data later. We might not
        !           164: want to give an attacker any clues about which blocks contain real data, and
        !           165: which are free space, so we want to write "noise" into all the disk blocks. So
1.1       jdf       166: we'll create a temporary `cgd`, configured with a random, unknown key.
                    167: 
                    168: First, we configure a `cgd` to use a random key:
                    169: 
1.3     ! jdf       170:     # cgdconfig -s cgd0 /dev/wd0e aes-cbc 128 < /dev/urandom
1.1       jdf       171: 
1.3     ! jdf       172: Now we can write zeros into the raw partition of our `cgd` (`/dev/rcgd0d` on
1.1       jdf       173: NetBSD/i386, `/dev/rcgd0c` on most other platforms):
                    174: 
                    175:     # dd if=/dev/zero of=/dev/rcgd0d bs=32k
                    176: 
1.3     ! jdf       177: The encrypted zeros will look like random data on disk. This might take a while
1.1       jdf       178: if you have a large disk. Once finished, unconfigure the random-key `cgd`:
                    179: 
                    180:     # cgdconfig -u cgd0
                    181: 
                    182: ### Creating the `cgd`
                    183: 
1.3     ! jdf       184: The
        !           185: [cgdconfig(8)](http://netbsd.gw.com/cgi-bin/man-cgi?cgdconfig+8+NetBSD-current)
        !           186: program, which manipulates `cgd` devices, uses parameters files to store such
        !           187: information as the encryption type, key length, and a random password salt for
        !           188: each `cgd`. These files are very important, and need to be kept safe - without
1.1       jdf       189: them, you will not be able to decrypt the data!
                    190: 
1.3     ! jdf       191: We'll generate a parameters file and write it into the default location (make
1.1       jdf       192: sure the directory `/etc/cgd` exists and is mode 700):
                    193: 
                    194:     # cgdconfig -g -V disklabel -o /etc/cgd/wd0e aes-cbc 256
                    195: 
1.3     ! jdf       196: This creates a parameters file `/etc/cgd/wd0e` describing a `cgd` using the
        !           197: `aes-cbc` cipher method, a key verification method of `disklabel`, and a key
1.1       jdf       198: length of `256` bits. It will look something like this:
                    199: 
                    200:     algorithm aes-cbc;
                    201:     iv-method encblkno;
                    202:     keylength 256;
                    203:     verify_method disklabel;
                    204:     keygen pkcs5_pbkdf2/sha1 {
                    205:             iterations 6275;
                    206:             salt AAAAgHTg/jKCd2ZJiOSGrgnadGw=;
                    207:     };
                    208: 
                    209: *Note*: Remember, you'll want to save this file somewhere safe later.
                    210: 
1.3     ! jdf       211: *Tip*: When creating the parameters file, `cgdconfig` reads from `/dev/random`
        !           212: to create the password salt. This read may block if there is not enough
        !           213: collected entropy in the random pool. This is unlikely, especially if you just
        !           214: finished overwriting the disk as in the previous step, but if it happens you can
        !           215: press keys on the console and/or move your mouse until the `rnd` device gathers
1.1       jdf       216: enough entropy.
                    217: 
1.3     ! jdf       218: Now it's time to create our `cgd`, for which we'll need a passphrase. This
        !           219: passphrase needs to be entered every time the `cgd` is opened, which is usually
        !           220: at each reboot. The encryption key is derived from this passphrase and the salt.
1.1       jdf       221: Make sure you choose something you won't forget, and others won't guess.
                    222: 
1.3     ! jdf       223: The first time we configure the `cgd`, there is no valid disklabel on the
        !           224: logical device, so the validation mechanism we want to use later won't work. We
1.1       jdf       225: override it this one time:
                    226: 
                    227:     # cgdconfig -V re-enter cgd0 /dev/wd0e
                    228: 
1.3     ! jdf       229: This will prompt twice for a matching passphrase, just in case you make a typo,
        !           230: which would otherwise leave you with a `cgd` encrypted with a passphrase that's
1.1       jdf       231: different to what you expected.
                    232: 
1.3     ! jdf       233: Now that we have a new `cgd`, we need to partition it and create filesystems.
        !           234: Recreate your previous partitions with all the same sizes, with the same letter
1.1       jdf       235: names.
                    236: 
1.3     ! jdf       237: *Tip*: Remember to use the `disklabel -I` argument, because you're creating an
1.1       jdf       238: initial label for a new disk.
                    239: 
1.3     ! jdf       240: *Note*: Although you want the sizes of your new partitions to be the same as the
        !           241: old, unencrypted ones, the offsets will be different because they're starting at
1.1       jdf       242: the beginning of this virtual disk.
                    243: 
1.3     ! jdf       244: Then, use
        !           245: [newfs(8)](http://netbsd.gw.com/cgi-bin/man-cgi?newfs+8+NetBSD-current) to
        !           246: create filesystems on all the relevant partitions. This time your partitions
1.1       jdf       247: will reflect the `cgd` disk names, for example:
                    248: 
                    249:     # newfs /dev/rcgd0h
                    250: 
                    251: ### Modifying configuration files
                    252: 
1.3     ! jdf       253: We've moved several filesystems to another (logical) disk, and we need to update
        !           254: `/etc/fstab` accordingly. Each partition will have the same letter (in this
        !           255: example), but will be on `cgd0` rather than `wd0`. So you'll have `/etc/fstab`
1.1       jdf       256: entries something like this:
                    257: 
                    258:     /dev/wd0a   /     ffs     rw    1 1
                    259:     /dev/cgd0b  none  swap    sw            0 0
                    260:     /dev/cgd0b  /tmp  mfs     rw,-s=132m    0 0
                    261:     /dev/cgd0e  /var  ffs     rw            1 2
                    262:     /dev/cgd0f  /usr  ffs     rw            1 2
                    263:     /dev/cgd0h  /home ffs     rw            1 2
                    264: 
1.3     ! jdf       265: *Note*: `/tmp` should be a separate filesystem, either `mfs` or `ffs`, inside
        !           266: the `cgd`, so that your temporary files are not stored in plain text in the `/`
1.1       jdf       267: filesystem.
                    268: 
1.3     ! jdf       269: Each time you reboot, you're going to need your `cgd` configured early, before
        !           270: [fsck(8)](http://netbsd.gw.com/cgi-bin/man-cgi?fsck+8+NetBSD-current) runs and
1.1       jdf       271: filesystems are mounted.
                    272: 
                    273: Put the following line in `/etc/cgd/cgd.conf`:
                    274: 
                    275:     cgd0    /dev/wd0e
                    276: 
                    277: This will use `/etc/cgd/wd0e` as config file for `cgd0`.
                    278: 
                    279: To finally enable cgd on each boot, put the following line into `/etc/rc.conf`:
                    280: 
                    281:     cgd=YES
                    282: 
1.3     ! jdf       283: You should now be prompted for `/dev/cgd0`'s passphrase whenever `/etc/rc`
1.1       jdf       284: starts.
                    285: 
                    286: ### Restoring data
                    287: 
1.3     ! jdf       288: Next, mount your new filesystems, and
        !           289: [restore(8)](http://netbsd.gw.com/cgi-bin/man-cgi?restore+8+NetBSD-current) your
        !           290: data into them. It often helps to have `/tmp` mounted properly first, as
        !           291: `restore` can use a fair amount of temporary space when extracting a large
1.1       jdf       292: dumpfile.
                    293: 
1.3     ! jdf       294: To test your changes to the boot configuration, umount the filesystems and
        !           295: unconfigure the `cgd`, so when you exit the single-user shell, *rc* will run
        !           296: like on a clean boot, prompting you for the passphrase and mounting your
        !           297: filesystems correctly. Now you can bring the system up to multi-user, and make
1.1       jdf       298: sure everything works as before.
                    299: 
                    300: ## Example: encrypted CDs/DVDs
                    301: 
                    302: ### Introduction
                    303: 
1.3     ! jdf       304: This section explains how to create and use encrypted CDs/DVDs with NetBSD (all
        !           305: I say about CDs here does also apply to DVDs). I assume that you have basic
        !           306: knowledge of cgd(4), so I will not explain what cgd is or what's inside it in
        !           307: detail. The same applies to vnd(4). One can make use of encrypted CDs after
        !           308: reading this howto, but for more detailed information about different cgd
1.1       jdf       309: configuration options, please read the previous parts or the manpages.
                    310: 
                    311: ### Creating an encrypted CD/DVD
                    312: 
1.3     ! jdf       313: cgd(4) provides highly secure encryption of whole partitions or disks.
        !           314: Unfortunately, creating "normal" CDs is not disklabeling something and running
        !           315: newfs on it. Neither can you just put a CDR into the drive, configure cgd and
        !           316: assume it to write encrypted data when syncing. Standard CDs contain at least an
        !           317: ISO-9660 filesystem created with mkisofs(8) from the
        !           318: [`sysutils/cdrtools`](http://ftp.NetBSD.org/pub/pkgsrc/current/pkgsrc/sysutils/cdrtools/README.html)
1.1       jdf       319: package. ISO images must *not* contain disklabels or cgd partitions.
                    320: 
1.3     ! jdf       321: But of course CD reader/writer hardware doesn't care about filesystems at all.
        !           322: You can write raw data to the CD if you like - or an encrypted FFS filesystem,
        !           323: which is what we'll do here. But be warned, there is NO way to read this CD with
1.1       jdf       324: any OS except NetBSD - not even other BSDs due to the lack of cgd.
                    325: 
                    326: The basic steps when creating an encrypted CD are:
                    327: 
                    328:  * Create an (empty) imagefile
                    329:  * Register it as a virtual disk using vnd(4)
                    330:  * Configure cgd inside the vnd disk
                    331:  * Copy content to the cgd
                    332:  * Unconfigure all (flush!)
                    333:  * Write the image on a CD
                    334: 
1.3     ! jdf       335: The first step when creating an encrypted CD is to create a single image file
        !           336: with dd. The image may not grow, so make it large enough to allow all CD content
        !           337: to fit into. Note that the whole image gets written to the CD later, so creating
        !           338: a 700 MB image for 100 MB content will still require a 700 MB write operation to
        !           339: the CD. Some info on DVDs here: DVDs are only 4.7 GB in marketing language.
        !           340: 4.7GB = 4.7 x 1024 x 1024 x 1024 = 5046586573 bytes. In fact, a DVD can only
        !           341: approximately hold 4.7 x 1000 x 1000 x 1000 = 4700000000 bytes, which is about
        !           342: 4482 MB or about 4.37 GB. Keep this in mind when creating DVD images. Don't
1.1       jdf       343: worry for CDs, they hold "real" 700 MB (734003200 Bytes).
                    344: 
                    345: Invoke all following commands as root!
                    346: 
                    347: For a CD:
                    348: 
                    349:     # dd if=/dev/zero of=image.img bs=1m count=700
                    350: 
                    351: or, for a DVD:
                    352: 
                    353:     # dd if=/dev/zero of=image.img bs=1m count=4482
                    354: 
1.3     ! jdf       355: Now configure a
        !           356: [vnd(4)](http://netbsd.gw.com/cgi-bin/man-cgi?vnd+4+NetBSD-5.0.1+i386)-pseudo
1.1       jdf       357: disk with the image:
                    358: 
                    359:     # vnconfig vnd0 image.img
                    360: 
1.3     ! jdf       361: In order to use cgd, a so-called parameter file, describing encryption
        !           362: parameters and a containing "password salt" must be generated. We'll call it
        !           363: `/etc/cgd/image` here. You can use one parameter file for several encrypted
        !           364: partitions (I use one different file for each host and a shared file `image` for
1.1       jdf       365: all removable media, but that's up to you).
                    366: 
1.3     ! jdf       367: I'll use AES-CBC with a keylength of 256 bits. Refer to
        !           368: [cgd(4)](http://netbsd.gw.com/cgi-bin/man-cgi?cgd+4+NetBSD-5.0.1+i386) and
        !           369: [cgdconfig(8)](http://netbsd.gw.com/cgi-bin/man-cgi?cgdconfig+8+NetBSD-5.0.1+i386)
1.1       jdf       370: for details and alternatives.
                    371: 
1.3     ! jdf       372: The following command will create the parameter file as `/etc/cgd/image`. *YOU
        !           373: DO NOT WANT TO INVOKE THE FOLLOWING COMMAND AGAIN* after you burnt any CD, since
        !           374: a recreated parameter file is a lost parameter file and you'll never access your
        !           375: encrypted CD again (the "salt" this file contains will differ among each call).
        !           376: Consider this file being *HOLY, BACKUP IT* and *BACKUP IT AGAIN!* Use switch -V
        !           377: to specify verification method "disklabel" for the CD (cgd cannot detect whether
1.1       jdf       378: you entered a valid password for the CD later when mounting it otherwise).
                    379: 
                    380:     # cgdconfig -g -V disklabel aes-cbc 256 > /etc/cgd/image
                    381: 
1.3     ! jdf       382: Now it's time to configure a cgd for our vnd drive. (Replace slice `d` with `c`
1.1       jdf       383: for all platforms that use `c` as the whole disk (where
1.3     ! jdf       384: `sysctl kern.rawpartition` prints `2`, not `3`); if you're on i386 or amd64, `d`
1.1       jdf       385: is OK for you):
                    386: 
                    387:     # cgdconfig -V re-enter cgd1 /dev/vnd0d /etc/cgd/image
                    388: 
1.3     ! jdf       389: The `-V re-enter` option is necessary as long as the cgd doesn't have a
        !           390: disklabel yet so we can access and configure it. This switch asks for a password
1.1       jdf       391: twice and uses it for encryption.
                    392: 
1.3     ! jdf       393: Now it's time to create a disklabel inside the cgd. The defaults of the label
1.1       jdf       394: are ok, so invoking disklabel with
                    395: 
                    396:     # disklabel -e -I cgd1
                    397: 
                    398: and leaving vi with `:wq` immediately will do.
                    399: 
                    400: Let's create a filesystem on the cgd, and finally mount it somewhere:
                    401: 
                    402:     # newfs /dev/rcgd1a
                    403:     # mount /dev/cgd1a /mnt
                    404: 
1.3     ! jdf       405: The cgd is alive! Now fill `/mnt` with content. When finished, reverse the
1.1       jdf       406: configuration process. The steps are:
                    407: 
                    408: 1.  Unmounting the cgd1a:
                    409: 
                    410:         # umount /mnt
                    411: 
                    412: 2.  Unconfiguring the cgd:
                    413: 
                    414:         # cgdconfig -u cgd1
                    415: 
                    416: 3.  Unconfiguring the vnd:
                    417: 
                    418:         # vnconfig -u vnd0
                    419: 
                    420: 
1.3     ! jdf       421: The following commands are examples to burn the images on CD or DVD. Please
        !           422: adjust the `dev=` for cdrecord or the `/dev/rcd0d` for growisofs. Note the
        !           423: `r` on the `rcd0d` *is* necessary with NetBSD. Growisofs is available in the
        !           424: [`sysutils/dvd+rw-tools`](http://ftp.NetBSD.org/pub/pkgsrc/current/pkgsrc/sysutils/dvd+rw-tools/README.html)
        !           425: package. Again, use `c` instead of `d` if this is the raw partition on your
1.1       jdf       426: platform.
                    427: 
                    428: Finally, write the image file to a CD:
                    429: 
                    430:     # cdrecord dev=/dev/rcd0d -v image.img
                    431: 
                    432: ...or to a DVD:
                    433: 
                    434:     # growisofs -dvd-compat -Z /dev/rcd0d=image.img
                    435: 
                    436: Congratulations! You've just created a really secure CD!
                    437: 
                    438: ### Using an encrypted CD/DVD
                    439: 
1.3     ! jdf       440: After creating an encrypted CD as described above, we're not done yet - what
        !           441: about mounting it again? One might guess, configuring the cgd on `/dev/cd0d` is
1.1       jdf       442: enough - no, it is not.
                    443: 
1.3     ! jdf       444: NetBSD cannot access FFS file systems on media that is not 512 bytes/sector
        !           445: format. It doesn't matter that the cgd on the CD is, since the CD's disklabel
1.1       jdf       446: the cgd resides in has 2048 bytes/sector.
                    447: 
1.3     ! jdf       448: But the CD driver cd(4) is smart enough to grant write access to the
        !           449: (emulated) disklabel on the CD. So before configuring the cgd, let's have a look
1.1       jdf       450: at the disklabel and modify it a bit:
                    451: 
                    452:     # disklabel -e cd0
                    453:     # /dev/rcd0d:
                    454:     type: ATAPI
                    455:     disk: mydisc
                    456:     label: fictitious
                    457:     flags: removable
                    458:     bytes/sector: 2048    # -- Change to 512 (= orig / 4)
                    459:     sectors/track: 100    # -- Change to 400 (= orig * 4)
                    460:     tracks/cylinder: 1
                    461:     sectors/cylinder: 100 # -- Change to 400 (= orig * 4)
                    462:     cylinders: 164
                    463:     total sectors: 16386  # -- Change to value of slice "d" (=65544)
                    464:     rpm: 300
                    465:     interleave: 1
                    466:     trackskew: 0
                    467:     cylinderskew: 0
                    468:     headswitch: 0           # microseconds
                    469:     track-to-track seek: 0  # microseconds
                    470:     drivedata: 0
                    471:     
                    472:     4 partitions:
                    473:     #     size  offset  fstype [fsize bsize cpg/sgs]
                    474:      a:   65544   0     4.2BSD  0     0     0  # (Cyl. 0 - 655+)
                    475:      d:   65544   0     ISO9660 0     0        # (Cyl. 0 - 655+)
                    476: 
                    477: Now as the disklabel is in 512 b/s format, accessing the CD is as easy as:
                    478: 
                    479:     # cgdconfig cgd1 /dev/cd0d /etc/cgd/image
                    480:     # mount -o ro /dev/cgd1a /mnt
                    481: 
1.3     ! jdf       482: Note that the cgd *MUST* be mounted read-only or you'll get illegal command
        !           483: errors from the cd(4) driver which can in some cases make even mounting a
1.1       jdf       484: CD-based cgd impossible!
                    485: 
                    486: Now we're done! Enjoy your secure CD!
                    487: 
                    488:     # ls /mnt
                    489: 
                    490: Remember you have to reverse all steps to remove the CD:
                    491: 
                    492:     # umount /mnt
                    493:     # cgdconfig -u cgd1
                    494:     # eject cd0
                    495: 
                    496: ## Suggestions and Warnings
                    497: 
1.3     ! jdf       498: You now have your filesystems encrypted within a `cgd`. When your machine is
        !           499: shut down, the data is protected, and can't be decrypted without the passphrase.
        !           500: However, there are still some dangers you should be aware of, and more you can
        !           501: do with `cgd`. This section documents several further suggestions and warnings
1.1       jdf       502:        that will help you use `cgd` effectively.
                    503: 
1.3     ! jdf       504:  * Use multiple `cgd`'s for different kinds of data, one mounted all the time
1.1       jdf       505:    and others mounted only when needed.
                    506: 
1.3     ! jdf       507:  * Use a `cgd` configured on top of a `vnd` made from a file on a remote network
        !           508:    fileserver (NFS, SMBFS, CODA, etc) to safely store private data on a shared
        !           509:    system. This is similar to the procedure for using encrypted CDs and DVDs
1.1       jdf       510:    described in [[Example: encrypted CDs/DVDs|guide/cgd#cryptocds]].
                    511: 
                    512: ### Using a random-key cgd for swap
                    513: 
1.3     ! jdf       514: You may want to use a dedicated random-key `cgd` for swap space, regenerating
        !           515: the key each reboot. The advantage of this is that once your machine is
        !           516: rebooted, any sensitive program memory contents that may have been paged out are
1.1       jdf       517: permanently unrecoverable, because the decryption key is never known to you.
                    518: 
1.3     ! jdf       519: We created a temporary `cgd` with a random key when scrubbing the disk in the
        !           520: example above, using a shorthand `cgdconfig -s` invocation to avoid creating a
1.1       jdf       521: parameters file.
                    522: 
1.3     ! jdf       523: The `cgdconfig` params file includes a *randomkey* keygen method. This is more
        !           524: appropriate for *permanent* random-key configurations, and facilitates the easy
1.1       jdf       525: automatic configuration of these volumes at boot time.
                    526: 
1.3     ! jdf       527: For example, if you wanted to convert your existing `/dev/wd0b` partition to a
        !           528: dedicated random-key cgd1, use the following command to generate
1.1       jdf       529: `/etc/cgd/wd0b`:
                    530: 
                    531:     # cgdconfig -g -o /etc/cgd/wd0b -V none -k randomkey blowfish-cbc
                    532: 
1.3     ! jdf       533: When using the randomkey keygen method, only verification method `none` can be
        !           534: used, because the contents of the new `cgd` are effectively random each time
        !           535: (the previous data decrypted with a random key). Likewise, the new disk will not
        !           536: have a valid label or partitions, and `swapctl` will complain about
1.1       jdf       537: configuring swap devices not marked as such in a disklabel.
                    538: 
1.3     ! jdf       539: In order to automate the process of labeling the disk, prepare an appropriate
        !           540: disklabel and save it to a file, for example `/etc/cgd/wd0b.disklabel`. Please
        !           541: refer to
        !           542: [disklabel(8)](http://netbsd.gw.com/cgi-bin/man-cgi?disklabel+8+NetBSD-5.0.1+i386)
1.1       jdf       543: for information about how to use `disklabel` to set up a swap partition.
                    544: 
1.3     ! jdf       545: On each reboot, to restore this saved label to the new `cgd`, create the
1.1       jdf       546: `/etc/rc.conf.d/cgd` file as below:
                    547: 
                    548:     swap_device="cgd1"
                    549:     swap_disklabel="/etc/cgd/wd0b.disklabel"
                    550:     start_postcmd="cgd_swap"
                    551:     
                    552:     cgd_swap()
                    553:     {
                    554:         if [ -f $swap_disklabel ]; then
                    555:             disklabel -R -r $swap_device $swap_disklabel
                    556:         fi
                    557:     }
                    558: 
1.3     ! jdf       559: The same technique could be extended to encompass using `newfs` to re-create
1.1       jdf       560: an `ffs` filesystem for `/tmp` if you didn't want to use `mfs`.
                    561: 
                    562: ### Warnings
                    563: 
1.3     ! jdf       564: Prevent cryptographic disasters by making sure you can always recover your
        !           565: passphrase and parameters file. Protect the parameters file from disclosure,
        !           566: perhaps by storing it on removable media as above, because the salt it contains
1.1       jdf       567: helps protect against dictionary attacks on the passphrase.
                    568: 
1.3     ! jdf       569: Keeping the data encrypted on your disk is all very well, but what about other
        !           570: copies? You already have at least one other such copy (the backup we used during
        !           571: this setup), and it's not encrypted. Piping `dump` through file-based
        !           572: encryption tools like `gpg` can be one way of addressing this issue, but make
        !           573: sure you have all the keys and tools you need to decrypt it to `restore` after
1.1       jdf       574: a disaster.
                    575: 
1.3     ! jdf       576: Like any form of software encryption, the `cgd` key stays in kernel memory while
        !           577: the device is configured, and may be accessible to privileged programs and
        !           578: users, such as `/dev/kmem` grovellers. Taking other system security steps, such
1.1       jdf       579: as running with elevated securelevel, is highly recommended.
                    580: 
1.3     ! jdf       581: Once the `cgd` volumes are mounted as normal filesystems, their contents are
        !           582: accessible like any other file. Take care of file permissions and ensure your
1.1       jdf       583: running system is protected against application and network security attack.
                    584: 
1.3     ! jdf       585: Avoid using suspend/resume, especially for laptops with a BIOS suspend-to-disk
        !           586: function. If an attacker can resume your laptop with the key still in memory, or
        !           587: read it from the suspend-to-disk memory image on the hard disk later, the whole
1.1       jdf       588: point of using `cgd` is lost.
                    589: 
                    590: ## Further Reading
                    591: 
                    592: The following resources contain more information on CGD:
                    593: 
                    594: ### Bibliography
                    595: 
1.2       jdf       596:  * [smackie-cgd]: *[NetBSD CGD Setup](http://www.bsdguides.org/guides/netbsd/misc/cgd_setup.php)*. Stuart Mackie.
                    597:  * [nycbug-cgd]: *[I want my cgd](http://genoverly.com/articles/view/5/) aka: I want an encrypted pseudo-device on my laptop*.
                    598:  * [elric-cgd]: *The original paper on [The CryptoGraphic Disk Driver](http://www.imrryr.org/~elric/cgd/cgd.pdf)*. Roland Dowdeswell and John Ioannidis.
                    599:  * [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.
                    600:  * [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       601: 

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