Manual browser: cgdconfig(8)

CGDCONFIG(8) System Manager's Manual CGDCONFIG(8)


cgdconfigconfiguration utility for the cryptographic disk driver


cgdconfig [-npv] [-V vmeth] cgd dev [paramsfile]

cgdconfig -C [-nv] [-f configfile]

cgdconfig -G [-nv] [-i ivmeth] [-k kgmeth] [-o outfile] paramsfile

cgdconfig -g [-nv] [-i ivmeth] [-k kgmeth] [-o outfile] alg [keylen]

cgdconfig -l [-cgd]

cgdconfig -s [-nv] [-i ivmeth] cgd dev alg [keylen]

cgdconfig -U [-nv] [-f configfile]

cgdconfig -u [-nv] cgd


cgdconfig is used to configure and unconfigure cryptographic disk devices (cgds) and to maintain the configuration files that are associated with them. For more information about cryptographic disk devices see cgd(4).

The options are as follows:

Configure all the devices listed in the cgd configuration file.
-f configfile
Specify the configuration file explicitly, rather than using the default configuration file /etc/cgd/cgd.conf.
Generate a new paramsfile (to stdout) using the values from paramsfile which will generate the same key. This may need to prompt for multiple passphrases.
Generate a paramsfile (to stdout).
-i ivmeth
Specify the IV method (default: encblkno1).
-k kgmeth
Specify the key generation method (default: pkcs5_pbkdf2/sha1).
-l [cgd]
List state of all devices or just the one cgd device. The verbosity level affects the output.
Do not actually configure or unconfigure a cryptographic disk device, but instead report the steps that would be taken.
-o outfile
When generating a paramsfile, store it in outfile.
Read all passphrases from stdin rather than /dev/tty. Passphrases are separated by newlines. Users of this flag must be able to predict the order in which passphrases are prompted. If this flag is specified then verification errors will cause the device in question to be unconfigured rather than prompting for the passphrase again.
Read the key from stdin.
Unconfigure all the devices listed in the cgd configuration file.
Unconfigure a cgd.
-V vmeth
Specify the verification method (default: none).
Be verbose. May be specified multiple times.

For more information about the cryptographic algorithms and IV methods supported, please refer to cgd(4).

Key Generation Methods

To generate the key which it will use, cgdconfig evaluates all of the key generation methods in the parameters file and uses the exclusive-or of the outputs of all the methods. The methods and descriptions are as follows:
This method requires a passphrase which is entered at configuration time. It is a salted hmac-based scheme detailed in “PKCS#5 v2.0: Password-Based Cryptography Standard”, RSA Laboratories, March 25, 1999, pages 8-10. PKCS #5 was also republished as RFC 2898.
This is an earlier, slightly incorrect and deprecated implementation of the above algorithm. It is retained for backwards compatibility with existing parameters files, and will be removed. Existing parameters files should be converted to use the correct method using the -G option, and a new passphrase.
This method stores its key in the parameters file.
The method simply reads /dev/random and uses the resulting bits as the key. It does not require a passphrase to be entered. This method is typically used to present disk devices that do not need to survive a reboot, such as the swap partition. It is also handy to facilitate overwriting the contents of a disk volume with meaningless data prior to use.
The method simply reads /dev/urandom and uses the resulting bits as the key. This is similar to the randomkey method, but it guarantees that cgdconfig will not stall waiting for hard-random bits (useful when configuring a cgd for swap at boot time). Note, however, that some or all of the bits used to generate the key may be obtained from a pseudo-random number generator, which may not be as secure as the entropy based hard-random number generator.
This method executes a shell command via popen(3) and reads the key from stdout.

Verification Method

The verification method is how cgdconfig determines if the generated key is correct. If the newly configured disk fails to verify, then cgdconfig will regenerate the key and re-configure the device. It only makes sense to specify a verification method if at least one of the key generation methods is error prone, e.g., uses a user-entered passphrase. The following verification methods are supported:

perform no verification.
scan for a valid disklabel.
scan for a valid FFS file system.
prompt for passphrase twice, and ensure entered passphrases are identical. This method only works with the pkcs5_pbkdf2/sha1 and pkcs5_pbkdf2 key generators.


The file /etc/cgd/cgd.conf is used to configure cgdconfig if either of -C or -U are specified. Each line of the file is composed of either two or three tokens: cgd, target, and optional paramsfile.

A ‘#’ character is interpreted as a comment and indicates that the rest of the line should be ignored. A ‘\’ at the end of a line indicates that the next line is a continuation of the current line.

See EXAMPLES for an example of /etc/cgd/cgd.conf.

Parameters File

The Parameters File contains the required information to generate the key and configure a device. These files are typically generated by the -g flag and not edited by hand. When a device is configured the default parameters file is constructed by taking the basename of the target disk and prepending /etc/cgd/ to it. E.g., if the target is /dev/sd0h, then the default parameters file will be /etc/cgd/sd0h.

It is possible to have more than one parameters file for a given disk which use different key generation methods but will generate the same key. To create a parameters file that is equivalent to an existing parameters file, use cgdconfig with the -G flag. See EXAMPLES for an example of this usage.

The parameters file contains a list of statements each terminated with a semi-colon. Some statements can contain statement-blocks which are either a single unadorned statement, or a brace-enclosed list of semicolon terminated statements. Three types of data are understood:

a 32 bit signed integer.
a string.
a length-encoded base64 string.

The following statements are defined:

algorithm string
Defines the cryptographic algorithm.
iv-method string
Defines the IV generation method.
keylength integer
Defines the length of the key.
verify_method string
Defines the verification method.
keygen string statement_block
Defines a key generation method. The statement_block contains statements that are specific to the key generation method.

The keygen statement's statement block may contain the following statements:

key string
The key. Only used for the storedkey key generation method.
cmd string
The command to execute. Only used for the shell_cmd key generation method.
iterations integer
The number of iterations. Only used for pkcs5_pbkdf2/sha1 and pkcs5_pbkdf2.
salt base64
The salt. Only used for pkcs5_pbkdf2/sha1 and pkcs5_pbkdf2.


configuration directory, used to store paramsfiles.
cgd configuration file.


To set up and configure a cgd that uses AES with a 192 bit key in CBC mode with the IV Method ‘encblkno1’ (encrypted block number):

	# cgdconfig -g -o /etc/cgd/wd0e aes-cbc 192 
	# cgdconfig cgd0 /dev/wd0e 
	/dev/wd0e's passphrase:

When using verification methods, the first time that we configure the disk the verification method will fail. We overcome this by supplying -V re-enter when we configure the first time to set up the disk. Here is the sequence of commands that is recommended:

	# cgdconfig -g -o /etc/cgd/wd0e -V disklabel aes-cbc 
	# cgdconfig -V re-enter cgd0 /dev/wd0e 
	/dev/wd0e's passphrase: 
	re-enter device's passphrase: 
	# disklabel -e -I cgd0 
	# cgdconfig -u cgd0 
	# cgdconfig cgd0 /dev/wd0e 
	/dev/wd0e's passphrase:

To scrub data from a disk before setting up a cgd:

	# cgdconfig -s cgd0 /dev/sd0e aes-cbc 256 < /dev/urandom 
	# dd if=/dev/zero of=/dev/rcgd0d bs=32k progress=512 
	# cgdconfig -u cgd0

To create a new parameters file that will generate the same key as an old parameters file:

	# cgdconfig -G -o newparamsfile oldparamsfile 
	old file's passphrase: 
	new file's passphrase:

To configure a cgd that uses Blowfish with a 200 bit key that it reads from stdin:

	# cgdconfig -s cgd0 /dev/sd0h blowfish-cbc 200

An example parameters file which uses PKCS#5 PBKDF2:

	algorithm aes-cbc; 
	iv-method encblkno1; 
	keylength 128; 
	verify_method none; 
	keygen pkcs5_pbkdf2/sha1 { 
		iterations 39361; 
		salt AAAAgMoHiYonye6Kog \ 

An example parameters file which stores its key locally:

	algorithm       aes-cbc; 
	iv-method       encblkno1; 
	keylength       256; 
	verify_method   none; 
	keygen storedkey key AAABAK3QO6d7xzLfrXTdsgg4 \ 

An example /etc/cgd/cgd.conf:

	# /etc/cgd/cgd.conf 
	# Configuration file for cryptographic disk devices 
	# cgd		target		[paramsfile] 
	cgd0		/dev/wd0e 
	cgd1		/dev/sd0h	/usr/local/etc/cgd/sd0h

Note the first entry will store the parameters file as /etc/cgd/wd0e. And use the entered passphrase to generate the key.

Although not required, the partition type cgd should be used in the disklabel for the cgd partition.


cgdconfig: could not calibrate pkcs5_pbkdf2
An error greater than 5% in calibration occured. This could be the result of dynamic processor frequency scaling technology. Ensure that the processor clock frequency remains static throughout the program's execution.



“PKCS #5 v2.0: Password-Based Cryptography Standard”, RSA Laboratories, March 25, 1999.


The cgdconfig utility appeared in NetBSD 2.0.


Since cgdconfig uses getpass(3) to read in the passphrase, it is limited to 128 characters.
December 3, 2012 NetBSD 7.0