PIM
PIM stands for "Personal Iterations Multiplier". It is a parameter that was introduced in VeraCrypt
1.12 and whose value controls the number of iterations used by the header key derivation function.
This value can be specified through the password dialog or in the command line.
If no PIM value is specified, VeraCrypt will use the default number of iterations used in versions prior
to 1.12 (see Header Key Derivation).
When a PIM value is specified, the number of iterations is calculated as follows:
For system encryption: Iterations = PIM x 2048
For non-system encryption and file containers: Iterations = 15000 + (PIM x 1000)
Prior to version 1.12, the security of a VeraCrypt volume was only based on the password strength
because VeraCrypt was using a fixed number of iterations.
With the introduction of PIM, VeraCrypt has a 2-dimensional security space for volumes based on the
couple (Password, PIM). This provides more flexibility for adjusting the desired security level while
also controlling the performance of the mount/boot operation.
PIM Usage
It is not mandatory to specify a PIM.
When creating a volume or when changing the password, the user has the possibility to specify a PIM
value by checking the "Use PIM" checkbox which in turn will make a PIM field available in the GUI
so a PIM value can be entered.
The PIM is treated like a secret value that must be entered by the user each time alongside the
password. If the incorrect PIM value is specified, the mount/boot operation will fail.
Using high PIM values leads to better security thanks to the increased number of iterations but it
comes with slower mounting/booting times.
With small PIM values, mounting/booting is quicker but this could decrease security if a weak
password is used.
During the creation of a volume or the encryption of the system, VeraCrypt forces the PIM value to be
greater than or equal to a certain minimal value when the password is less than 20 characters. This
check is done in order to ensure that, for short passwords, the security level is at least equal to the
default level provided by an empty PIM.
The PIM minimal value for short passwords is 98 for system encryption and 485 for non-system
encryption and files containers. For password with 20 characters and more, the PIM minimal value is
1. In all cases, leaving the PIM empty or setting its value to 0 will make VeraCrypt use the default
high number of iterations as explained in section Header Key Derivation.
Motivations behind using a custom PIM value can be:
Add an extra secret parameter (PIM) that an attacker will have to guess
Increase security level by using large PIM values to thwart future development of brute force
attacks.
Speeding up booting or mounting through the use of a small PIM value (less than 98 for system
encryption and less than 485 for the other cases)
