Keyfiles
Keyfile is a file whose content is combined with a password (for information on the method used to combine a keyfile with password, see the section
Keyfiles
in the chapter
Technical Details). Until the correct keyfile is provided, no volume that uses the keyfile can be mounted.
You do not have to use keyfiles. However, using keyfiles has some advantages:
- May improve protection against brute force attacks (significant particularly if the volume password is not very strong).
- Allows the use of security tokens and smart cards (see below).
- Allows multiple users to mount a single volume using different user passwords or PINs. Just give each user a security token or smart card containing the same TrueCrypt keyfile and let them choose their personal password or PIN that will protect their security token or smart card.
-
Allows managing multi-user shared
access (all keyfile holders must present their keyfiles before a volume can be mounted).
Any kind of file (for example, .txt, .exe, mp3**, .avi) can be used as a TrueCrypt keyfile (however, we recommend that you prefer compressed files, such as .mp3, .jpg, .zip, etc).
Note that TrueCrypt never modifies the keyfile contents. You can select more than one keyfile; the order does not matter. You can also let TrueCrypt generate a file with random content and use it as a keyfile. To do so, select Tools > Keyfile Generator.
Note: Keyfiles are currently not supported for system encryption.
WARNING: If password caching is enabled, the password cache also contains the processed contents of keyfiles used to successfully mount a volume. Then it is possible to remount the volume even if the keyfile is not available/accessible.
To prevent this, click 'Wipe Cache
' or disable password caching (for more information, please see the subsection
'Settings -> Preferences'
, item
'Cache passwords in driver memory'
in the section Program Menu).
Keyfiles Dialog Window
If you want to use keyfiles (i.e. "apply" them) when creating or mounting volumes, or changing passwords, look for the 'Use keyfiles' option and the
Keyfiles
button below a password input field.
These control elements appear in various dialog windows and always have the same functions. Check the Use keyfiles
option and click
Keyfiles.
The keyfile dialog window should appear where you can specify keyfiles (to do so, click
Add Files or
Add Token Files)
or
keyfile search paths (click Add Path).
Security Tokens and Smart Cards
TrueCrypt can directly use keyfiles stored on a security token or smart card that complies with the PKCS #11 (2.0 or later) standard [23] and that allows the user to store a file (data object) on the token/card. To use such files as TrueCrypt keyfiles, click
Add Token Files
(in the keyfile dialog window).
Access to a keyfile stored on a security token or smart card is typically protected by PIN codes, which can be entered either using a hardware PIN pad or via the TrueCrypt GUI. It can also be protected by other means, such as fingerprint readers.
In order to allow TrueCrypt to access a security token or smart card, you need to install a PKCS #11 (2.0 or later) software library for the token or smart card first. Such a library may be supplied with the device or it may be available for download from the website of the vendor or other third parties.
If your security token or smart card does not contain any file (data object) that you could use as a TrueCrypt keyfile, you can use TrueCrypt to import any file to the token or smart card (if it is supported by the device). To do so, follow these steps:
- In the keyfile dialog window, click
Add Token Files.
- If the token or smart card is protected by a PIN, password, or other means (such as a fingerprint reader), authenticate yourself (for example, by entering the PIN using a hardware PIN pad).
-
The 'Security Token Keyfile' dialog window should appear. In it, click Import Keyfile to Token
and then select the file you want to import to the token or smart card.
Note that you can import for example 512-bit keyfiles with random content generated by TrueCrypt (see
Tools > Keyfile Generator
below).
To close all opened security token sessions, either select
Tools
> Close All Security Token Sessions
or define and use a hotkey combination (Settings
> Hot Keys > Close All Security Token Sessions).
Keyfile Search Path
By adding a folder in the keyfile dialog window (click
Add Path), you specify a
keyfile search path. All files found in the keyfile search path* will be used as keyfiles except files that have the Hidden file attribute set.
Important: Note that folders (and files they contain) and hidden files found in a keyfile search path are ignored.
Keyfile search paths are especially useful if you, for example, store keyfiles on a USB memory stick that you carry with you. You can set the drive letter of the USB memory stick as a default keyfile search path. To do so, select Settings
->
Default Keyfiles. Then click
Add Path, browse to the drive letter assigned to the USB memory stick, and click
OK. Now each time you mount a volume (and if the option
Use keyfiles
is checked in the password dialog window), TrueCrypt will scan the path and use all files that it finds on the USB memory stick as keyfiles.
WARNING: When you add a folder (as opposed to a file) to the list of keyfiles, only the path is remembered, not the filenames! This means e.g. that if you create a new file in the folder or if you copy an additional file to the folder, then all volumes that used keyfiles from the folder will be impossible to mount (until you remove the newly added file from the folder).
Empty Password & Keyfile
When a keyfile is used, the password may be empty, so the keyfile may become the only item necessary to mount the volume (which we do not recommend). If default keyfiles are set and enabled when mounting a volume, then before prompting for a password, TrueCrypt first automatically attempts to mount using an empty password plus default keyfiles (however, this does not apply to the 'Auto-Mount Devices' function). If you need to set Mount Options (e.g., mount as read-only, protect hidden volume etc.) for a volume being mounted this way, hold down the
Control
(Ctrl) key while clicking
Mount
(or select
Mount with Options
from the
Volumes
menu). This will open the
Mount Options
dialog.
Quick Selection
Keyfiles and keyfile search paths can be quickly selected in the following ways:
- Right-click the
Keyfiles
button in the password entry dialog window and select one of the menu items.
- Drag the corresponding file/folder icons to the keyfile dialog window or to the password entry dialog.
Volumes -> Add/Remove Keyfiles to/from Volume
This function allows you to re-encrypt a volume header with a header encryption key derived from any number of keyfiles (with or without a password), or no keyfiles at all. Thus, a volume which is possible to mount using only a password can be converted to a volume that require keyfiles (in addition to the password) in order to be possible to mount. Note that the volume header contains the master encryption key with which the volume is encrypted. Therefore, the data stored on the volume will not
be lost after you use this function.
This function can also be used to change/set volume keyfiles (i.e., to remove some or all keyfiles, and to apply new ones).
Remark: This function is internally equal to the Password Change function.
When TrueCrypt re-encrypts a volume header, the original volume header is first overwritten 256 times with random data to prevent adversaries from using techniques such as magnetic force microscopy or magnetic force scanning tunneling microscopy [17] to recover the overwritten header (however, see also the chapter
Security Requirements and Precautions).
Volumes -> Remove All Keyfiles from Volume
This function allows you to re-encrypt a volume header with a header encryption key derived from a password and no keyfiles (so that it can be mounted using only a password, without any keyfiles). Note that the volume header contains the master encryption key with which the volume is encrypted. Therefore, the data stored on the volume will not
be lost after you use this function.
Remark: This function is internally equal to the Password Change function.
When TrueCrypt re-encrypts a volume header, the original volume header is first overwritten 256 times with random data to prevent adversaries from using techniques such as magnetic force microscopy or magnetic force scanning tunneling microscopy [17] to recover the overwritten header (however, see also the chapter
Security Requirements and Precautions).
Tools > Keyfile Generator
You can use this function to generate a file with random content, which you can use as a keyfile (recommended). This function uses the TrueCrypt Random Number Generator. Note that the resulting file size is always 64 bytes (i.e., 512 bits), which is also the maximum possible TrueCrypt password length.
Settings -> Default Keyfiles
Use this function to set default keyfiles and/or default keyfile search paths. This function is particularly useful if you, for example, store keyfiles on a USB memory stick that you carry with you. You can add its drive letter to the default keyfile configuration. To do so, click
Add Path, browse to the drive letter assigned to the USB memory stick, and click
OK. Now each time you mount a volume (and if
Use keyfiles
is checked in the password dialog), TrueCrypt will scan the path and use all files that it finds there as keyfiles.
WARNING: When you add a folder (as opposed to a file) to your default keyfile list, only the path is remembered, not the filenames! This means e.g. that if you create a new file in the folder or if you copy an additional file to the folder, then all volumes that used keyfiles from the folder will be impossible to mount (until you remove the newly added file from the folder).
IMPORTANT: Note that when you set default keyfiles and/or default keyfile search paths, the filenames and paths are saved unencrypted in the file
Default Keyfiles.xml
. For more information, please see the chapter
TrueCrypt System Files & Application Data.
* Found at the time when you are mounting the volume, changing its password, or performing any other operation that involves re-encryption of the volume header.
** However, if you use an MP3 file as a keyfile, you must ensure that no program modifies the ID3 tags within the MP3 file (e.g. song title, name of artist, etc.). Otherwise, it will be impossible to mount volumes that use the keyfile.
See also:
Main Program Window,
Technical Details
