UNIX random devices and utilities

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21
votes
4answers
8k views

Why does dd from /dev/random give different file sizes?

I am running the following command on an ubuntu system: dd if=/dev/random of=rand bs=1K count=2 However, every time I run it, I end up with a file of a different size. Why is this? How can I ...
11
votes
4answers
5k views

Create random data with dd and get “partial read warning”. Is the data after the warning now really random?

I create a 1TB file with random data with dd if=/dev/urandom of=file bs=1M count=1000000. Now I check with kill -SIGUSR1 <PID> the progress and get the following: 691581+0 Datensätze ein 691580+...
30
votes
2answers
24k views

How can I populate a file with random data?

How can I create a new file and fill it with 1 Gigabyte worth of random data? I need this to test some software. I would prefer to use /dev/random or /dev/urandom.
11
votes
2answers
3k views

What keeps draining entropy?

If I do watch cat /proc/sys/kernel/random/entropy_avail I see that my systems entropy slowly increases over time, until it reaches the 180-190 range at which point it drops down to around 120-130. The ...
7
votes
1answer
379 views

Can you explain the entropy estimate used in random.c

/dev/random uses the timings of kernel interupts to add to the entropy pool. The amount of entropy in the pool is tracked in a variable named entropy_count. Here is the relevant snippet of code from ...
3
votes
2answers
395 views

Is it bad to have a low entropy in /dev/random?

I wonder whether for the average Linux user it is considered as bad -from a point of view of security or any other relevant viewpoints- to have no or almost no entropy left in /dev/random. Edit: I ...
15
votes
4answers
6k views

Tool for measuring entropy quality?

Is there a tool available for Linux systems that can measure the "quality" of entropy on the system? I know how to count the entropy: cat /proc/sys/kernel/random/entropy_avail And I know that some ...
22
votes
9answers
45k views

Generate random numbers in specific range

After googling a bit I couldn't find a simple way to use a shell command to generate a random decimal integer number included in a specific range, that is between a minimum and a maximum. I read ...
9
votes
5answers
7k views

Fast Way to Randomize HD?

I've read about how to make hard drives secure for encryption, and one of the steps is to write random bits to the drive, in order to make the encrypted data indistinguishable from the rest of the ...
7
votes
2answers
2k views

RSA 2048 keypair generation: via openssl 0.5s via gpg 30s, why the difference?

RSA 2048 keypair generation: via openssl 0.5s via gpg 30s, why the difference There are several programs which can gerate RSA public/private keypairs GnuPG/OpenPGP for instance has a wizzard being ...
5
votes
2answers
877 views

How to determine which processes are using how much entropy from /dev/urandom

Doing fuser -v /dev/urandom tells me which processes currently have /dev/urandom open, but only that. Is there any was to determine anything about how much entropy each one is using up over time? ...
9
votes
2answers
3k views

Adding “random number entropy” for GPG keys?

In the following video: Linux HOWTO: Secure Your Data with PGP, Part 2, you are shown how to create a key pair with gpg. At about 1:50, the instructor says the following: While the key is being ...
7
votes
3answers
1k views

Lightweight utility/program to run a command after a random delay

I need to randomize the time before a given command starts. I realize it's relatively trivial to do this within a script, or to write a "wrapper" script to do this, but I'm wondering if anyone knows a ...
4
votes
1answer
280 views

measure amount of data read from /dev/random

background I have written a collection of bash scripts (most of them in German only yet but if you are interested; download the archive not the single scripts) which help users create high-quality ...
2
votes
2answers
2k views

random number needed

I need a command line script that will generate a random integer between 1 and 6. I'm using Ubuntu with bash. I was working on this a couple of months ago using 'bc', but never got it to work ...
2
votes
4answers
969 views

Overwriting a Disk

Should I use: find / -type f -exec shred -uvz -nX or just good old dd if=/dev/urandom of=/dev/sda Is one faster or more secure than the other?
0
votes
2answers
3k views

How to generate random IP addresses

$ nmap -n -iR 0 -sL > RANDOM-IPS-TMP.txt $ grep -o "[0-9]*\.[0-9]*\.[0-9]*\.[0-9]*" RANDOM-IPS-TMP.txt | egrep -v "10.*|172.[16-32].*|192.168.*|[224-255].*" > RANDOM-IPS.txt egrep: Invalid ...