# DUHK attack and OpenVPN 

## Background 
October 24, 2017 Shaanan Cohney, Nadia Heninger and Matthew D. Green released [Practical state recovery attacks against legacy RNG implementations](https://duhkattack.com/paper.pdf) (PDF) which have been known as the DUHK attack: [Don't Use Hard-coded Keys](https://duhkattack.com/).  This relates in particular to a Random Number Generator (RNG) algorithm known as *ANSI X9.31 RNG*.

The ANSI X9.31 RNG has been deprecated as part of the FIPS specification as of January 2016 and is further discouraged elsewhere too.

## How is OpenVPN affected?

OpenVPN is ***not*** affected by DUHK.  All random number generation in OpenVPN is based upon the SSL/TLS libraries and, to our knowledge, neither OpenSSL nor mbed TLS depends on the ANSI X9.31 RNG algorithm.  Further, OpenVPN does not use or deploy any hard-coded keys or seeds for the RNG.  And both OpenSSL and mbed TLS libraries implements re-seeding of the RNG at regular intervals.