In FIPS 140-2 Part 2:Interfaces and Port in the security policy of product told : 1- "the output data path is provided by the data interfaces and is logically disconnected from processes performing key generation or zeroization. No key information will be output through the data output interface when the module zeroizes keys." What is this meaning? 2- And this "The output data path shall be logically disconnected from the circuitry and processes while performing key generation, manual key entry, or key zeroization."


2 Answers 2


It's cryptographic marketing spiel to convince end users to pay double.

This is about hardware. All it means is that the cryptographic key(s), typically generated via a true random process, is/are never sent outside of the physical device. The best way to illustrate this is by example: https://www.maximintegrated.com/en/design/partners-and-technology/design-technology/chipdna-puf-technology.html. They say:-

Most importantly, the ChipDNA secure key never resides statically in registers or memory, nor does it ever leave the electrical boundary of the IC.

My above example is a physical unclonable function (PUF) designed for secure authentication. You might have one in a posh printer cartridge or embedded microcontroller.

if one user generates a key another user takes management and control. how devices do this?

That would be the case for a key generator/ true random number generator or quantum key distribution node. But not for authentication. There is no need to give out a private key in authentication use cases. The device seals itself off from the external world to either securely sign unpredictable keys, or completely destroy them with no possibility to recall. That way the signature/destroy processes can't be interfered with.

That simply means new keys (TRNG in the schematics) are obfuscated by some one way function; SHA-3 in this case. And in conjunction with a "SHA3 SECRET", probably a general device key owned by Maxim (and the PUF part). That creates an ersatz keyed hash function. The SHA3 SECRET key(s) is/are not directly accessible by any input/output circuits.

It's unlikely that users will ever know the true details as this is proprietary intellectual property and can't be easily audited. FIPS 140-2 is just the applicable standard to which such devices are made.

Zeroization is what it sounds like. That and the key obfuscation are to prevent key extraction discussed in this question.

  • $\begingroup$ SHA3-256......? $\endgroup$
    – Paul Uszak
    Commented Jun 29, 2021 at 12:29
  • $\begingroup$ Why would this be a marketing spiel? The fact that while key generation is going on you should (at least logically i.e. through SW) disconnect output is perfectly sensibly as it lowers the chance of any un/intentional key secret leakage. The same situation is for zeroization. In reality you would like the input/output to be disconnected whenever any operations with the key are performed ideally. As to whether or not the details can or can't be audited depends on who you are. Powerful governments regularly do audit these. $\endgroup$
    – DRF
    Commented Jun 29, 2021 at 15:11
  • $\begingroup$ Hi, for this "while key generation is going on you should (at least logically i.e. through SW) disconnect output is perfectly sensibly" how? if one user generates a key another user takes management and control. how devices do this? $\endgroup$
    – Juliet
    Commented Jun 30, 2021 at 13:53
  • $\begingroup$ @Juliet DRF is correct in that it's not spiel. It's technically right, but I just critique the un-necessessarily techie language (hence the plain English link). $\endgroup$
    – Paul Uszak
    Commented Jun 30, 2021 at 14:07
  • $\begingroup$ What's up with that link at the bottom of your answer? $\endgroup$
    – JohnEye
    Commented Jun 30, 2021 at 14:21

I'm reading this as: Interfaces and ports should not leak information that might be related to the keys being generated, manually entered, or zeroized (erased). Otherwise said: keep secrets secret from observers having hooked these communication paths.


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