randomizing source with /dev/urandom

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redsock

Joined: 09 Oct 2009
Posts: 435
Location: Australia

redsock 30 May 2014, 02:55

Attempting to read a byte from /dev/urandom like:

Code:

virtual at 0
    file '/dev/urandom',1
    load randbyte from 0
end virtual

results in:

file '/dev/urandom',1
error: value out of range.

Any other creative way to get a random byte into compile-time?

Cheers
[/code]

30 May 2014, 02:55

redsock

Joined: 09 Oct 2009
Posts: 435
Location: Australia

redsock 30 May 2014, 03:10

Further details of what fasm is doing:

After a quick strace, fasm is trying to determine the file length of /dev/urandom and is of course unable to.

open("//dev/urandom", O_RDONLY) = 3
lseek(3, 0, SEEK_END) = 0

thus, value out of range is because of the end returning 0... Hmm.

30 May 2014, 03:10

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20445
Location: In your JS exploiting you and your system

revolution 30 May 2014, 05:13

You could do any of:

Write a small program to write a single random byte to a file periodically
Edit fasm source code to force it to read the requested bytes for zero length streams
Manually edit you source code with a new value before assembling
Increase the clock speed of you system to make it unreliable and produce random binaries each time
Wait hundreds (thousands?) of years for the bits to decay into a different state
Others?

30 May 2014, 05:13

gens

Joined: 18 Feb 2013
Posts: 161

gens 30 May 2014, 19:47

redsock wrote:

Further details of what fasm is doing:

After a quick strace, fasm is trying to determine the file length of /dev/urandom and is of course unable to.

open("//dev/urandom", O_RDONLY) = 3
lseek(3, 0, SEEK_END) = 0

thus, value out of range is because of the end returning 0... Hmm.

do a
dd if=/dev/urandom of=./tmp_rand_file bs=1 count=n

where n is how much bytes

30 May 2014, 19:47

redsock

Joined: 09 Oct 2009
Posts: 435
Location: Australia

redsock 30 May 2014, 22:51

revolution wrote:

You could do any of:
Write a small program to write a single random byte to a file periodically
Edit fasm source code to force it to read the requested bytes for zero length streams
Manually edit you source code with a new value before assembling
Increase the clock speed of you system to make it unreliable and produce random binaries each time
Wait hundreds (thousands?) of years for the bits to decay into a different state
Others?

BAHAH, love your work revolution!

It is actually for fixed Diffie-Hellman public parameters, which are fine to stay relatively static (when sufficiently large), but I thought the compile-time randomized selection from a pool of my verified safe primes would be a cool thing to add.

Grabbing bytes from the PRNG before compile time certainly works, I was just hoping for a funky way to do it in the fasm source itself instead of scripting the build process and/or Makefiles.

Cheers and thanks for the chuckles anyway, hahah! Legend!

This one in particular:

Quote:

Increase the clock speed of you system to make it unreliable and produce random binaries each time

HA! that is a crackup.

30 May 2014, 22:51

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