This software is still at the experimental stage. No guarantee for any damage which might be caused by the use of this software. Caveat emptor.

Note well: providing incorrect permission and unauthenticated or unscreened data to the device driver /dev/trng may degrade the quality of /dev/random, /dev/urandom, and the security of the entire FreeBSD operating system.

To accomodate True Random Number Generator (TRNG) random bits into FreeBSD kernel.

Note: this driver is for FreeBSD 11.0 and later only.

• FreeBSD amd64 12.0-PRERELEASE r340660 (for 0.6.0 and later)
• For FreeBSD 11.x, use tag 0.5.2

The driver in trng.c works as /dev/trng. It accepts up to 1024-byte write operation to feed the written data as an entropy string by calling random_harvest_fast(9) multiple times. 16 bytes in maximum are passed for each time when the harvesting function is called.

feedtrng.c is a C code example to transfer TRNG data from a tty device to /dev/trng. The code sets input tty disciplines and lock the tty, then feed the contents to /dev/trng. Some things to consider:

• The tty input are sampled as 512-byte blocks. Each block is concatenated to 64-byte hashed result of SHA512, and again hashed by SHA512, to obtain 64-byte (512-bit) hashed output. The hashed result is sent to the kernel. Compression ratio: 1/8. This whitening can be disabled by -t option.
• When running in the default mode, the first block (512 bytes) from the tty device is discarded to prevent unstable data of TRNG from being transferred to /dev/trng. This data truncation does not happen when the data is redirected to stdout.

The source to write to /dev/trng must be a real TRNG. Possible candidates are:

• avrhwrng, an experimental hardware on Arduino Duemilanove/UNO, claiming ~10kbytes/sec (disclaimer: Kenji Rikitake develops the software and hardware)
• NeuG, claiming ~80kbytes/sec generation speed
• OneRNG, claiming ~44kbytes/sec generation speed
• TrueRNG 2, claiming ~43.5kbytes/sec generation speed

Currently, the random bits in the given entropy strings are estimated as 1/2 of the given bits, which is a common practice for accepting TRNG sequences in the FreeBSD crypto device drivers.

The entropy source provided by /dev/trng is currently indicated as RANDOM_NET_ETHER. Set sysctl kern.random.sys.harvest.ethernet=1 to enable harvesting from the Ethernet traffic. See random(4) for the details.

• 20-NOV-2018: 0.6.0 (Modification for FreeBSD 12.0 applied)
• 11-AUG-2017: 0.5.2 (Add rc.d script, last version for FreeBSD 11.x)
• 15-NOV-2016: 0.5.1 (Apply clang-format, Fix loops in feedtrng, add macros in trng)
• 14-NOV-2016: 0.5.0 (FreeBSD 11 or later only, remove rndtest(4) support)
• 10-JUL-2016: 0.4.0 (Preliminary fix for FreeBSD 11)
• 10-OCT-2015: 0.3.3 (Use SHA512 hash for 1:8 compression as default)
• 7-OCT-2015: 0.3.2 (Make feedtrng to discard the first block from tty)
• 23-SEP-2015: 0.3.1 (Fix termios; now CLOCAL cleared, modem control enabled)
• 20-SEP-2015: 0.3.0 (Installation simplified, Makefiles streamlined)
• 19-SEP-2015: 0.2.3 (Fix feedtrng tty read(2) bug)
• 13-AUG-2015: 0.2.2 (Add feedtrng -o option for redirecting output to stdout)
• 12-AUG-2015: 0.2.1 (Fix feedtrng tcsetattr bug)
• 12-AUG-2015: 0.2.0 (Revise feedtrng to set tty line disciplines, exclusive access)
• 11-AUG-2015: 0.1.1 (Revise feedtrng to accept /dev/cua* device name)
• 6-AUG-2015: 0.1.0 (Use Newbus driver, enable rndtest driver hook)
• 4-AUG-2015: 0.0.5 (Fix trng dev code)
• 30-JUL-2015: 0.0.4 (Fix on code)
• 29-JUL-2015: 0.0.3 (Fix feedtrng code)
• 28-JUL-2015: 0.0.1 (Initial release)

make clean all
# run following as a superuser
# trng.ko will be added to /boot/modules/
# feedtrng will be added to /usr/local/bin/
make install
# /dev/trng has the owner uucp:dialer and permission 0660 as default
kldload trng.ko

# Only /dev/cua* devices are accepted
feedtrng -d /dev/cuaU0
# only the basename(3) part is used and attached to `/dev/` directly
# so this is also OK
feedtrng -d cuaU0
# tty speed [bps] can be set (9600 ~ 1000000, default 115200)
feedtrng -d cuaU1 -s 9600
# for usage
feedtrng -h

• Copy local-rc.d/feedtrng as /usr/local/etc/rc.d/feedtrng
• Set feedtrng_enable and feedtrng_device in /etc/rc.conf accordingly

# result of `sudo stty -f /dev/cuaU0` (sudo needed to override TIOCEXCL)
speed 115200 baud;
lflags: -icanon -isig -iexten -echo
iflags: -icrnl -ixon -imaxbel ignbrk -brkint
oflags: -opost tab0
cflags: cs8 -parenb -clocal

BSD 2-clause. See LICENSE.

SHA512 hashing code are from the following page: Fast SHA-2 hashes in x86 assembly by Project Nayuki. The related code are distributed under the MIT License.

This part is no longer applicable for /dev/trng. See rndtest.md for the further details.

• FreeBSD Architecture Handbook: Section 9.3 https://www.freebsd.org/doc/en_US.ISO8859-1/books/arch-handbook/driverbasics-char.html
• Writing a kernel module for FreeBSD
• Joseph Kong, FreeBSD Device Drivers, No Starch Press, May 2012, ISBN 978-1-59327-204-3