Operation Manual

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When creating a volume, encrypting a system partition/drive, or changing passwords/keyfiles, you
must not allow any third party to choose or modify the password/keyfile(s) before/while the volume
is created or the password/keyfiles(s) changed. For example, you must not use any password
generators (whether website applications or locally run programs) where you are not sure that they
are high-quality and uncontrolled by an attacker, and keyfiles must not be files that you download
from the internet or that are accessible to other users of the computer (whether they are
administrators or not).
Changing Passwords and Keyfiles
Note that the volume header (which is encrypted with a header key derived from a
password/keyfile) contains the master key (not to be confused with the password) with which the
volume is encrypted. If an adversary is allowed to make a copy of your volume before you change
the volume password and/or keyfile(s), he may be able to use his copy or fragment (the old
header) of the VeraCrypt volume to mount your volume using a compromised password and/or
compromised keyfiles that were necessary to mount the volume before you changed the volume
password and/or keyfile(s).
If you are not sure whether an adversary knows your password (or has your keyfiles) and whether
he has a copy of your volume when you need to change its password and/or keyfiles, it is strongly
recommended that you create a new VeraCrypt volume and move files from the old volume to the
new volume (the new volume will have a different master key).
Also note that if an adversary knows your password (or has your keyfiles) and has access to your
volume, he may be able to retrieve and keep its master key. If he does, he may be able to decrypt
your volume even after you change its password and/or keyfile(s) (because the master key does
not change when you change the volume password and/or keyfiles). In such a case, create a new
VeraCrypt volume and move all files from the old volume to this new one.
The following sections of this chapter contain additional information pertaining to possible security
issues connected with changing passwords and/or keyfiles:
 Security Requirements and Precautions
 Journaling File Systems
 Defragmenting
 Reallocated Sectors
Trim Operation
Some storage devices (e.g., some solid-state drives, including USB flash drives) use so-called
‘trim’ operation to mark drive sectors as free e.g. when a file is deleted. Consequently, such sectors
may contain unencrypted zeroes or other undefined data (unencrypted) even if they are located
within a part of the drive that is encrypted by VeraCrypt. VeraCrypt does not block the trim
operation on partitions that are within the key scope of system encryption (see chapter System
Encryption) (unless a hidden operating system is running – see section Hidden Operating System)
and under Linux on all volumes that use the Linux native kernel cryptographic services. In those
cases, the adversary will be able to tell which sectors contain free space (and may be able to use
this information for further analysis and attacks) and plausible deniability (see chapter Plausible
Deniability) may be negatively affected. If you want to avoid those issues, do not use system
encryption on drives that use the trim operation and, under Linux, either configure VeraCrypt not to