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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:
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).
See also the section Choosing Passwords and Keyfiles in the chapter Security Requirements and Precautions.
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).
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:
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).
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.
Important: Note that folders (and files they contain) found in keyfile search paths 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).
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.
Keyfiles and keyfile search paths can be quickly selected in the following ways:
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).
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).
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.
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.
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