[OpenWrt-Devel] [PATCH RFC 0/5] ath79: add micro non-physical true RNG based on timing jitter

Petr Štetiar ynezz at true.cz
Mon May 20 12:13:20 EDT 2019


this patch series is an RFC which attempts to fix some of the current
urandom-seed based flaws.

First, simply writing to /dev/urandom does not increase the kernel's
entropy count, this casuses processes obtaining randomness to block.
Particularly processes using OpenSSL's RAND_bytes() will block until the
kernel emits 'random: crng init done'. This can take upwards of twenty

According to random(4) the entropy count is only increased when using the
RNDADDENTROPY ioctl, which urandom-seed currently doesn't use when feeding the
kernel RNG.

Second, urandom-seed is using /etc/urandom.seed file to seed the kernel's RNG
machinery upon every boot. The problem is, that this file is created only once
during first-boot and then reused on every consecutive boot, so pretty much

So this patch series removes urandom-seed package in favor of urngd, which is
new micro non-physical true random number generator (system service) based on
timing jitter.

Using the Jitter RNG core, the urngd provides an entropy source that
feeds into the Linux /dev/random device if its entropy runs low. It
updates the /dev/random entropy estimator such that the newly provided
entropy unblocks /dev/random.

The seeding of /dev/random also ensures that /dev/urandom benefits from
entropy. Especially during boot time, when the entropy of Linux is low,
the Jitter RNGd provides a source of sufficient entropy.

Some RNG init time numbers from qca9563 (TP-Link Archer C7 v5):

 [   12.045693] random: crng init done        (urngd)
 [  120.043132] random: crng init done        (urandom-seed)

Flash space details:

 urngd:        + 4579 b
 getrandom:    - 1635 b
 urandom-seed: -  841 b
 diff          + 2103 b

Cc: Stephan Mueller <smueller at chronox.de>
Cc: Dustin Lundquist <d.lundquist at temperednetworks.com>

Petr Štetiar (5):
  urng: add micro non-physical true RNG based on timing jitter
  ubox: move getrandom into separate getrandom package
  base-files: move urandom seed bits into separate package
  build: add urandom-seed to the default packages set
  ath79: make urngd default RNG seed source

 include/target.mk                                  |  2 +-
 package/base-files/Makefile                        | 11 ++++-
 package/base-files/files/etc/init.d/urandom_seed   | 12 ------
 .../base-files/files/lib/preinit/81_urandom_seed   | 24 -----------
 package/base-files/files/sbin/urandom_seed         | 20 ---------
 package/system/ubox/Makefile                       | 17 ++++++--
 package/system/urandom-seed/Makefile               | 32 +++++++++++++++
 .../urandom-seed/files/etc/init.d/urandom_seed     | 12 ++++++
 .../urandom-seed/files/lib/preinit/81_urandom_seed | 24 +++++++++++
 .../system/urandom-seed/files/sbin/urandom_seed    | 20 +++++++++
 package/system/urngd/Makefile                      | 48 ++++++++++++++++++++++
 package/system/urngd/files/urngd.init              | 21 ++++++++++
 target/linux/ath79/Makefile                        |  3 +-
 13 files changed, 184 insertions(+), 62 deletions(-)
 delete mode 100755 package/base-files/files/etc/init.d/urandom_seed
 delete mode 100644 package/base-files/files/lib/preinit/81_urandom_seed
 delete mode 100755 package/base-files/files/sbin/urandom_seed
 create mode 100644 package/system/urandom-seed/Makefile
 create mode 100755 package/system/urandom-seed/files/etc/init.d/urandom_seed
 create mode 100644 package/system/urandom-seed/files/lib/preinit/81_urandom_seed
 create mode 100755 package/system/urandom-seed/files/sbin/urandom_seed
 create mode 100644 package/system/urngd/Makefile
 create mode 100755 package/system/urngd/files/urngd.init


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