Requirement 1

All output data exiting the cryptographic module via the "data output" interface shall only pass through the output data path. The output data path shall be logically disconnected from the circuitry and processes while performing manual key entry.

Requirement 2

During key entry, the manually entered values may be temporarily displayed to allow visual verification and to improve accuracy.

To display the values for visual verification, the data has to be passed via the output data path which will contradict with requirement 1. What am I missing here?

  • 1
    The display that shows the entered values does not need to be the output path.
    – Tobi Nary
    Nov 13, 2017 at 16:38
  • 1
    Most of the cases(headless boxes), the display will be external to crypto boundary connected via trust channel or directly attached cable which are output paths.
    – Shashank V
    Nov 13, 2017 at 16:58

2 Answers 2


No the manual entry referred here is done by an external device (i.e. a pinpad) which is connected to the cryptographic module.When you enter the key you give an input to the cryptographic module so the output data path can be disconnected. Moreover the external device can have a display screen where the key holder will see what he types.

The meaning of requirement 2 is that the manual entry of the key on the device display doesn't have to be hidden (in contrast with password hidden with stars when you log in most of the systems). So the key holder entering is key can verify what he enter.

  • Makes sense with pin pad example. How to interpret this for other devices say a switch or router where the terminal/screen which displays the characters will be an external device and keyboard is used as input device to enter the keys?
    – Shashank V
    Nov 13, 2017 at 18:49
  • Same you can have a server with screen/keyboard connected to the crypto module (e.g. by network or PCI). You have to understand that the key displayed here doesn't comes from the crypto module but from the manual entry directly. But be careful for FIPS-140 2 level 3 and more you need what they call a trusted path between the crypto module and the key loading device. Nov 13, 2017 at 19:46

The logical consequence of these two requirements is that the temporary display permitted by (2) may not be output from the module. It must be a display of data that has not yet entered the module.

The boundary of a cryptographic module does not have to be fully defined in physical terms: it needs to define a physical perimeter, but can exclude subsystems defined in logical terms (provided that these subsystems have no impact on the cryptographic operation). A typical definition of a cryptographic module that allows key entry with echo would exclude the part of the system that provides the local echo. When certifying a whole device, this can be done by defining the physical boundary as the device, but defining the logical boundary in a way that excludes the user interface.

At levels 3 and above, a physically separated port or trusted path is required for key entry. This can be, for example, a keypad device, which may have its own local display; that display is allowed to echo keys that the user is typing in, but if it does that then it must not be used to display data output. A trusted path could be, for example, a window that is protected from snooping, and that echoes what the user is typing, but does not display output from the cryptographic processor at any time.

  • Can the trusted path be an SSH connection or an IPSEC tunnel etc?
    – Shashank V
    Nov 15, 2017 at 6:41
  • @aviator Yes, if your SSH/IPSEC stack and its configuration are inside the perimeter of the FIPS certification. Nov 15, 2017 at 9:29

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