docs/169089: [geli] [PATCH] geli(8) needs clarity concerning key scope/type/purpose

[John W. O'Brien]

The following reply was made to PR docs/169089; it has been noted by GNATS.

From: "John W. O'Brien" <john at saltant.com>
To: bug-followup at FreeBSD.org
Cc:  
Subject: Re: docs/169089: [geli] [PATCH] geli(8) needs clarity concerning
 key scope/type/purpose
Date: Mon, 18 Jun 2012 08:46:42 -0400

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 See attached patch that includes updates based on feedback from pjd@
 on freebsd-geom at .
 
 - - /keylen/datakeylen/ change vetoed
 - - fix markup style
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 Index: geli.8
 ===================================================================
 --- geli.8	(revision 236978)
 +++ geli.8	(working copy)
 @@ -24,7 +24,7 @@
  .\"
  .\" $FreeBSD$
  .\"
 -.Dd April 28, 2012
 +.Dd June 18, 2012
  .Dt GELI 8
  .Os
  .Sh NAME
 @@ -186,14 +186,15 @@
  or
  .Nm HMAC/SHA512 .
  .It
 -Can create a key from a couple of components (user entered passphrase, random
 -bits from a file, etc.).
 +Can create a User Key from up to two, piecewise components: a passphrase
 +entered via prompt or read from one or more passfiles; a keyfile read from
 +one or more files.
  .It
  Allows encryption of the root partition.
  The user will be asked for the
  passphrase before the root file system is mounted.
  .It
 -The passphrase of the user is strengthened with:
 +Strengthens the passphrase component of the User Key with:
  .Rs
  .%A B. Kaliski
  .%T "PKCS #5: Password-Based Cryptography Specification, Version 2.0."
 @@ -201,7 +202,7 @@
  .%N 2898
  .Re
  .It
 -Allows the use of two independent keys (e.g., a
 +Allows the use of two independent User Keys (e.g., a
  .Qq "user key"
  and a
  .Qq "company key" ) .
 @@ -210,8 +211,8 @@
  .Nm
  performs simple sector-to-sector encryption.
  .It
 -Allows Master Keys to be backed up and restored,
 -so that if a user has to quickly destroy his keys,
 +Allows the encrypted Master Key to be backed up and restored,
 +so that if a user has to quickly destroy key material,
  it is possible to get the data back by restoring keys from
  backup.
  .It
 @@ -219,8 +220,8 @@
  (so users do not have to remember to detach providers after unmounting
  the file systems).
  .It
 -Allows attaching a provider with a random, one-time key - useful for swap
 -partitions and temporary file systems.
 +Allows attaching a provider with a random, one-time Master Key -
 +useful for swap partitions and temporary file systems.
  .It
  Allows verification of data integrity (data authentication).
  .It
 @@ -233,7 +234,8 @@
  .Bl -tag -width ".Cm configure"
  .It Cm init
  Initialize the provider which needs to be encrypted.
 -Here you can set up the cryptographic algorithm to use, key length, etc.
 +Here you can set up the cryptographic algorithm to use, Data Key length,
 +etc.
  The last sector of the provider is used to store metadata.
  The
  .Cm init
 @@ -289,37 +291,58 @@
  The default and recommended algorithm is
  .Nm AES-XTS .
  .It Fl i Ar iterations
 -Number of iterations to use with PKCS#5v2.
 +Number of iterations to use with PKCS#5v2 when processing User Key
 +passphrase component.
  If this option is not specified,
  .Nm
  will find the number of iterations which is equal to 2 seconds of crypto work.
  If 0 is given, PKCS#5v2 will not be used.
 +PKCS#5v2 processing is performed once, after all parts of the passphrase
 +component have been read.
  .It Fl J Ar newpassfile
 -Specifies a file which contains the passphrase or its part.
 +Specifies a file which contains the passphrase component of the User Key
 +(or part of it).
  If
  .Ar newpassfile
  is given as -, standard input will be used.
  Only the first line (excluding new-line character) is taken from the given file.
 -This argument can be specified multiple times.
 +This argument can be specified multiple times, which has the effect of
 +reassembling a single passphrase split across multiple files.
 +Cannot be combined with the
 +.Fl P
 +option.
  .It Fl K Ar newkeyfile
 -Specifies a file which contains part of the key.
 +Specifies a file which contains the keyfile component of the User Key
 +(or part of it).
  If
  .Ar newkeyfile
  is given as -, standard input will be used.
 -This argument can be specified multiple times.
 +This argument can be specified multiple times, which has the effect of
 +reassembling a single keyfile split across multiple keyfile parts.
  .It Fl l Ar keylen
 -Key length to use with the given cryptographic algorithm.
 -If not given, the default key length for the given algorithm is used, which is:
 -128 for
 -.Nm AES-XTS ,
 -.Nm AES-CBC ,
 -.Nm Blowfish-CBC
 -and
 -.Nm Camellia-CBC
 -and 192 for
 -.Nm 3DES-CBC .
 +Data Key length to use with the given cryptographic algorithm.
 +If the length is not specified, the selected algorithm uses its
 +.Em default
 +key length.
 +.Bl -ohang -offset indent
 +.It Nm AES-XTS
 +.Em 128 ,
 +256
 +.It Nm AES-CBC , Nm Camilla-CBC
 +.Em 128 ,
 +192,
 +256
 +.It Nm Blowfish-CBC
 +.Em 128
 ++ n * 32, for n=[0..10]
 +.It Nm 3DES-CBC
 +.Em 192
 +.El
  .It Fl P
 -Do not use passphrase as the key component.
 +Do not use a passphrase as a component of the User Key.
 +Cannot be combined with the
 +.Fl J
 +option.
  .It Fl s Ar sectorsize
  Change decrypted provider's sector size.
  Increasing the sector size allows increased performance,
 @@ -337,9 +360,9 @@
  .El
  .It Cm attach
  Attach the given provider.
 -The master key will be decrypted using the given
 -passphrase/keyfile and a new GEOM provider will be created using the given
 -provider's name with an
 +The encrypted Master Key will be loaded from the metadata and decrypted
 +using the given passphrase/keyfile and a new GEOM provider will be created
 +using the given provider's name with an
  .Qq .eli
  suffix.
  .Pp
 @@ -357,28 +380,33 @@
  .Cm detach
  subcommand.
  .It Fl j Ar passfile
 -Specifies a file which contains the passphrase or its part.
 +Specifies a file which contains the passphrase component of the User Key
 +(or part of it).
  For more information see the description of the
  .Fl J
  option for the
  .Cm init
  subcommand.
  .It Fl k Ar keyfile
 -Specifies a file which contains part of the key.
 +Specifies a file which contains the keyfile component of the User Key
 +(or part of it).
  For more information see the description of the
  .Fl K
  option for the
  .Cm init
  subcommand.
  .It Fl p
 -Do not use passphrase as the key component.
 +Do not use a passphrase as a component of the User Key.
 +Cannot be combined with the
 +.Fl j
 +option.
  .It Fl r
  Attach read-only provider.
  It will not be opened for writing.
  .El
  .It Cm detach
  Detach the given providers, which means remove the devfs entry
 -and clear the keys from memory.
 +and clear the Master Key and Data Keys from memory.
  .Pp
  Additional options include:
  .Bl -tag -width ".Fl f"
 @@ -391,7 +419,7 @@
  last time even if it was only opened for reading.
  .El
  .It Cm onetime
 -Attach the given providers with random, one-time keys.
 +Attach the given providers with a random, one-time (ephemeral) Master Key.
  The command can be used to encrypt swap partitions or temporary file systems.
  .Pp
  Additional options include:
 @@ -415,7 +443,7 @@
  .Cm attach
  subcommand.
  .It Fl l Ar keylen
 -Key length to use with the given cryptographic algorithm.
 +Data Key length to use with the given cryptographic algorithm.
  For more information, see the description of the
  .Cm init
  subcommand.
 @@ -439,15 +467,18 @@
  Remove the BOOT flag from the given providers.
  .El
  .It Cm setkey
 -Change or setup (if not yet initialized) selected key.
 -There is one master key, which can be encrypted with two independent user keys.
 +Install a copy of the Master Key into the selected slot, encrypted with
 +a new User Key.
 +If the selected slot is populated, replace the existing copy.
 +A provider has one Master Key, which can be stored in one or both slots,
 +each encrypted with an independent User Key.
  With the
  .Cm init
  subcommand, only key number 0 is initialized.
 -The key can always be changed: for an attached provider,
 +The User Key can be changed at any time: for an attached provider,
  for a detached provider, or on the backup file.
  When a provider is attached, the user does not have to provide
 -an old passphrase/keyfile.
 +an existing passphrase/keyfile.
  .Pp
  Additional options include:
  .Bl -tag -width ".Fl J Ar newpassfile"
 @@ -458,44 +489,54 @@
  .Cm setkey
  subcommand, only one key has to be defined and this key must be changed.
  .It Fl j Ar passfile
 -Specifies a file which contains the old passphrase or its part.
 +Specifies a file which contains the passphrase component of a current User Key
 +(or part of it).
  .It Fl J Ar newpassfile
 -Specifies a file which contains the new passphrase or its part.
 +Specifies a file which contains the passphrase component of the new User Key
 +(or part of it).
  .It Fl k Ar keyfile
 -Specifies a file which contains part of the old key.
 +Specifies a file which contains the keyfile component of a current User Key
 +(or part of it).
  .It Fl K Ar newkeyfile
 -Specifies a file which contains part of the new key.
 +Specifies a file which contains the keyfile component of the new User Key
 +(or part of it).
  .It Fl n Ar keyno
 -Specifies the number of the key to change (could be 0 or 1).
 +Specifies the index number of the Master Key copy to change (could be 0 or 1).
  If the provider is attached and no key number is given, the key
  used for attaching the provider will be changed.
  If the provider is detached (or we are operating on a backup file)
 -and no key number is given, the key decrypted with the passphrase/keyfile
 -will be changed.
 +and no key number is given, the first Master Key copy to be successfully
 +decrypted with the provided User Key passphrase/keyfile will be changed.
  .It Fl p
 -Do not use passphrase as the old key component.
 +Do not use a passphrase as a component of the current User Key.
 +Cannot be combined with the
 +.Fl j
 +option.
  .It Fl P
 -Do not use passphrase as the new key component.
 +Do not use a passphrase as a component of the new User Key.
 +Cannot be combined with the
 +.Fl J
 +option.
  .El
  .It Cm delkey
 -Destroy (overwrite with random data) the selected key.
 +Destroy (overwrite with random data) the selected Master Key copy.
  If one is destroying keys for an attached provider, the provider
 -will not be detached even if all keys are destroyed.
 +will not be detached even if all copies of the Master Key are destroyed.
  It can even be rescued with the
  .Cm setkey
 -subcommand.
 +subcommand because the Master Key is still in memory.
  .Pp
  Additional options include:
  .Bl -tag -width ".Fl a Ar keyno"
  .It Fl a
 -Destroy all keys (does not need
 +Destroy all copies of the Master Key (does not need
  .Fl f
  option).
  .It Fl f
  Force key destruction.
 -This option is needed to destroy the last key.
 +This option is needed to destroy the last copy of the Master Key.
  .It Fl n Ar keyno
 -Specifies the key number.
 +Specifies the index number of the Master Key copy.
  If the provider is attached and no key number is given, the key
  used for attaching the provider will be destroyed.
  If provider is detached (or we are operating on a backup file) the key number
 @@ -503,8 +544,8 @@
  .El
  .It Cm kill
  This command should be used only in emergency situations.
 -It will destroy all the keys on a given provider and will detach it forcibly
 -(if it is attached).
 +It will destroy all copies of the Master Key on a given provider and will
 +detach it forcibly (if it is attached).
  This is absolutely a one-way command - if you do not have a metadata
  backup, your data is gone for good.
  In case the provider was attached with the
 @@ -542,8 +583,8 @@
  .El
  .It Cm suspend
  Suspend device by waiting for all inflight requests to finish, clearing all
 -sensitive information (like keys) from kernel memory, and blocking all
 -further I/O requests until the
 +sensitive information (like the Master Key and Data Keys) from kernel memory,
 +and blocking all further I/O requests until the
  .Cm resume
  subcommand is executed.
  This functionality is useful for laptops: when one wants to suspend a
 @@ -553,8 +594,8 @@
  the
  .Cm suspend
  subcommand can be used.
 -Any access to the encrypted device will be blocked until the keys are
 -recovered through the
 +Any access to the encrypted device will be blocked until the Master Key is
 +reloaded through the
  .Cm resume
  subcommand.
  Thus there is no need to close nor unmount anything.
 @@ -584,21 +625,26 @@
  Additional options include:
  .Bl -tag -width ".Fl j Ar passfile"
  .It Fl j Ar passfile
 -Specifies a file which contains the passphrase or its part.
 +Specifies a file which contains the passphrase component of the User Key
 +(or part of it).
  For more information see the description of the
  .Fl J
  option for the
  .Cm init
  subcommand.
  .It Fl k Ar keyfile
 -Specifies a file which contains part of the key.
 +Specifies a file which contains the keyfile component of the User Key
 +(or part of it).
  For more information see the description of the
  .Fl K
  option for the
  .Cm init
  subcommand.
  .It Fl p
 -Do not use passphrase as the key component.
 +Do not use a passphrase as a component of the User Key.
 +Cannot be combined with the
 +.Fl j
 +option.
  .El
  .It Cm resize
  Inform
 @@ -626,6 +672,9 @@
  subcommand will print metadata version used by each of them.
  .It Cm clear
  Clear metadata from the given providers.
 +.Em WARNING :
 +This will erase with zeros the encrypted Master Key copies stored in the
 +metadata.
  .It Cm dump
  Dump metadata stored on the given providers.
  .It Cm list
 @@ -647,6 +696,36 @@
  .It Fl v
  Be more verbose.
  .El
 +.Sh KEY SUMMARY
 +.Ss Master Key
 +Upon
 +.Cm init ,
 +the
 +.Nm
 +utility generates a random Master Key for the provider.
 +The Master Key never changes during the lifetime of the provider.
 +Each copy of the provider metadata, active or backed up to a file, can store
 +up to two, independently-encrypted copies of the Master Key.
 +.Ss User Key
 +Each stored copy of the Master Key is encrypted with a User Key, which
 +is generated by the
 +.Nm
 +utility from a passphrase and/or a keyfile.
 +The
 +.Nm
 +utility first reads all parts of the keyfile in the order specified on the
 +command line, then reads all parts of the stored passphrase in the order
 +specified on the command line.
 +If no passphrase parts are specified, the system prompts the user to enter
 +the passphrase.
 +The passphrase is optionally strengthened by PKCS#5v2.
 +The User Key is a digest computed over the concatenated keyfile and passphrase.
 +.Ss Data Key
 +During operation, one or more Data Keys are deterministically derived by
 +the kernel from the Master Key and cached in memory.
 +The number of Data Keys used by a given provider, and the way they are
 +derived, depend on the GELI version and whether the provider is configured to
 +use data authentication.
  .Sh SYSCTL VARIABLES
  The following
  .Xr sysctl 8
 @@ -677,7 +756,7 @@
  This variable should be set in
  .Pa /boot/loader.conf .
  .It Va kern.geom.eli.overwrites : No 5
 -Specifies how many times the Master-Key will be overwritten
 +Specifies how many times the Master Key will be overwritten
  with random values when it is destroyed.
  After this operation it is filled with zeros.
  .It Va kern.geom.eli.visible_passphrase : No 0
 @@ -699,18 +778,19 @@
  crypto requests with one interrupt.
  The crypto card and the driver has to support this feature.
  .It Va kern.geom.eli.key_cache_limit : No 8192
 -Specifies how many encryption keys to cache.
 +Specifies how many Data Keys to cache.
  The default limit
  (8192 keys) will allow caching of all keys for a 4TB provider with 512 byte
  sectors and will take around 1MB of memory.
  .It Va kern.geom.eli.key_cache_hits
 -Reports how many times we were looking up a key and it was already in cache.
 -This sysctl is not updated for providers that need less keys than the limit
 -specified in
 +Reports how many times we were looking up a Data Key and it was already in
 +cache.
 +This sysctl is not updated for providers that need fewer Data Keys than
 +the limit specified in
  .Va kern.geom.eli.key_cache_limit .
  .It Va kern.geom.eli.key_cache_misses
 -Reports how many times we were looking up a key and it was not in cache.
 -This sysctl is not updated for providers that need fewer keys than the limit
 +Reports how many times we were looking up a Data Key and it was not in cache.
 +This sysctl is not updated for providers that need fewer Data Keys than the limit
  specified in
  .Va kern.geom.eli.key_cache_limit .
  .El
 @@ -738,7 +818,7 @@
  # geli detach da2.eli
  .Ed
  .Pp
 -Create an encrypted provider, but use two keys:
 +Create an encrypted provider, but use two User Keys:
  one for your employee and one for you as the company's security officer
  (so it's not a tragedy if the employee
  .Qq accidentally
 @@ -760,7 +840,7 @@
  # dd if=/dev/random of=/mnt/pendrive/keys/`hostname` bs=64 count=1
  # geli init -P -K /mnt/pendrive/keys/`hostname` /dev/ad0s1e
  # geli backup /dev/ad0s1e /mnt/pendrive/backups/`hostname`
 -(use key number 0, so the encrypted Master Key will be overwritten by this)
 +(use key number 0, so the encrypted Master Key will be re-encrypted by this)
  # geli setkey -n 0 -k /mnt/pendrive/keys/`hostname` /dev/ad0s1e
  (allow the user to enter his passphrase)
  Enter new passphrase:
 @@ -776,8 +856,8 @@
  .Pp
  The example below shows how to configure two providers which will be attached
  on boot (before the root file system is mounted).
 -One of them is using passphrase and three keyfiles and the other is using only a
 -keyfile:
 +One of them is using passphrase and three keyfile parts and the other is
 +using only a keyfile in one part:
  .Bd -literal -offset indent
  # dd if=/dev/random of=/dev/da0 bs=1m
  # dd if=/dev/random of=/boot/keys/da0.key0 bs=32k count=1
 
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