Entropy and randomness - Revision history

Sertonix: update link

2023-08-25T11:44:28Z

update link

← Older revision		Revision as of 11:44, 25 August 2023
Line 120:		Line 120:
	[https://blog.cloudflare.com/ensuring-randomness-with-linuxs-random-number-generator Cloudflare]		[https://blog.cloudflare.com/ensuring-randomness-with-linuxs-random-number-generator Cloudflare]

	[https://~~tools~~.ietf.org/html/rfc4086 RFC 4086 - Randomness Requirements for Security]		[https://datatracker.ietf.org/doc/html/rfc4086 RFC 4086 - Randomness Requirements for Security]

	[https://calomel.org/entropy_random_number_generators.html calomel.org]		[https://calomel.org/entropy_random_number_generators.html calomel.org]

Sertonix: + Category:Security

2023-08-25T11:43:42Z

+ Category:Security

← Older revision		Revision as of 11:43, 25 August 2023
Line 137:		Line 137:

	[[Category:Server]]		[[Category:Server]]
			[[Category:Security]]

Zcrayfish: /* Haveged */ Upgraded all urls to https.

2023-07-29T06:45:58Z

Haveged: Upgraded all urls to https.

← Older revision		Revision as of 06:45, 29 July 2023
Line 51:		Line 51:
	=== Haveged ===		=== Haveged ===

	[~~http~~://www.issihosts.com/haveged/ Haveged] generates entropy based on [~~http~~://www.issihosts.com/haveged/flutter.html CPU flutter]. The entropy is buffered and fed into the entropy pool when write_wakeup_threshold is reached. Write a value (the number of bits) to it if you wish to change it:		[https://www.issihosts.com/haveged/ Haveged] generates entropy based on [https://www.issihosts.com/haveged/flutter.html CPU flutter]. The entropy is buffered and fed into the entropy pool when write_wakeup_threshold is reached. Write a value (the number of bits) to it if you wish to change it:

	{{Cmd\|echo "1024" > /proc/sys/kernel/random/write_wakeup_threshold}}		{{Cmd\|echo "1024" > /proc/sys/kernel/random/write_wakeup_threshold}}
Line 63:		Line 63:
	{{Cmd\|apk -U add haveged && rc-service haveged start && rc-update add haveged}}		{{Cmd\|apk -U add haveged && rc-service haveged start && rc-update add haveged}}

	[~~http~~://linux.die.net/man/8/haveged Further configuration] is possible however the defaults should work fine out of the box.		[https://linux.die.net/man/8/haveged Further configuration] is possible however the defaults should work fine out of the box.

	=== Other possibilities ===		=== Other possibilities ===

Zcrayfish: /* Other possibilities */ Removed a massive number of references to dead links.

2023-07-29T06:43:33Z

Other possibilities: Removed a massive number of references to dead links.

@@ Line 67: / Line 67: @@
 === Other possibilities ===
-Some other possibilites for entropy generation are:
+It is also possible to replace /dev/random with [https://egd.sourceforge.net/ EGD, the Entropy Gathering Daemon], or to use this on systems that are not able to support /dev/random.  However, this is not required (or recommended) under normal circumstances.
 == Testing entropy with ENT ==

Zcrayfish: /* Testing entropy with ENT */ URL cleanup.

2023-07-29T06:40:19Z

Testing entropy with ENT: URL cleanup.

← Older revision		Revision as of 06:40, 29 July 2023
Line 85:		Line 85:
	== Testing entropy with ENT ==		== Testing entropy with ENT ==

	It is possible to [~~http~~://en.wikipedia.org/wiki/Randomness_test test] entropy to see how statistically random it is. Generally, such tests only reveal part of the picture, since some numbers can pass statistical entropy tests whilst they are not actually random. Failing a statistical randomness test is not a good indicator of course!		It is possible to [https://en.wikipedia.org/wiki/Randomness_test test] entropy to see how statistically random it is. Generally, such tests only reveal part of the picture, since some numbers can pass statistical entropy tests whilst they are not actually random. Failing a statistical randomness test is not a good indicator of course!

	Make a folder for testing, and get hold of [~~http~~://www.fourmilab.ch/random/ ENT]:		Make a folder for testing, and get hold of [https://www.fourmilab.ch/random/ ENT]:

	<pre>		<pre>
	mkdir /tmp/test/make		mkdir /tmp/test/make
	cd /tmp/test/make		cd /tmp/test/make
	wget ~~http~~://www.fourmilab.ch/random/random.zip		wget https://www.fourmilab.ch/random/random.zip
	unzip random.zip		unzip random.zip
	make		make

Zcrayfish: /* Other tests */ URL cleanup.

2023-07-29T06:39:21Z

Other tests: URL cleanup.

← Older revision		Revision as of 06:39, 29 July 2023
Line 124:		Line 124:
	=== Other tests ===		=== Other tests ===

	Other tests include [~~http~~://~~www~~.stat.fsu.edu~~/pub~~/diehard/ diehard] and [~~http~~://~~www~~.phy.duke.edu/~rgb/General/dieharder.php dieharder]		Other tests include [https://ani.stat.fsu.edu/diehard/ diehard] and [https://webhome.phy.duke.edu/~rgb/General/dieharder.php dieharder]

	== Further reading ==		== Further reading ==

Zcrayfish: /* Further reading */ URL cleanup.

2023-07-29T06:38:03Z

Zcrayfish: /* Introduction */ URL cleanup

2023-07-29T06:33:24Z

Introduction: URL cleanup

Zcrayfish: /* Other possibilities */ Marked a dead link.

2021-12-20T18:57:07Z

Other possibilities: Marked a dead link.

← Older revision		Revision as of 18:57, 20 December 2021
Line 75:		Line 75:
	*[http://www.vanheusden.com/aed/ audio entropy daemon] - requires alsa development libraries and an audio device. Generates entropy by reading from audio device and de-baising data.		*[http://www.vanheusden.com/aed/ audio entropy daemon] - requires alsa development libraries and an audio device. Generates entropy by reading from audio device and de-baising data.

	*[http://vladz.devzero.fr/guchaos.php GUChaos] - "Give Us Chaos" provides on-demand entropy, by retrieving random blocks of bytes from the [http://www.random.org/ Random.org] website, and transforms them with a [http://en.wikipedia.org/wiki/Substitution_cipher polynumeric substitution cipher] before adding them to /dev/random until the entropy pool is filled.		*[http://vladz.devzero.fr/guchaos.php GUChaos]{{dead link}} - "Give Us Chaos" provides on-demand entropy, by retrieving random blocks of bytes from the [http://www.random.org/ Random.org] website, and transforms them with a [http://en.wikipedia.org/wiki/Substitution_cipher polynumeric substitution cipher] before adding them to /dev/random until the entropy pool is filled.

	and hardware entropy generators such as:		and hardware entropy generators such as:

Zcrayfish: /* Haveged */ Use pkg template instead of external link. (note: this package is obsolete)

2021-12-17T18:52:23Z

Haveged: Use pkg template instead of external link. (note: this package is obsolete)

← Older revision		Revision as of 18:52, 17 December 2021
Line 59:		Line 59:
	{{Cmd\|haveged -w 1024}}		{{Cmd\|haveged -w 1024}}

	Install ~~[http://alpinelinux.org/apk/main/x86_64/~~haveged ~~haveged]~~, then start and set to autostart at boot:		Install {{pkg\|haveged}}, then start and set to autostart at boot:

	{{Cmd\|apk -U add haveged && rc-service haveged start && rc-update add haveged}}		{{Cmd\|apk -U add haveged && rc-service haveged start && rc-update add haveged}}

	[http://linux.die.net/man/8/haveged Further configuration] is possible however the defaults should work fine out of the box.		[http://linux.die.net/man/8/haveged Further configuration] is possible however the defaults should work fine out of the box.

	=== Other possibilities ===		=== Other possibilities ===

← Older revision		Revision as of 06:38, 29 July 2023
Line 128:		Line 128:
	== Further reading ==		== Further reading ==

	[~~http~~://rsmith.home.xs4all.nl/howto/fun-with-encryption-and-randomness.html visualising randomness]		[https://rsmith.home.xs4all.nl/howto/fun-with-encryption-and-randomness.html visualising randomness]

	[~~http~~://www.linuxfromscratch.org/hints/downloads/files/entropy.txt linux from scratch]		[https://www.linuxfromscratch.org/hints/downloads/files/entropy.txt linux from scratch]

	[~~http~~://blog.cloudflare.com/ensuring-randomness-with-linuxs-random-number-generator Cloudflare]		[https://blog.cloudflare.com/ensuring-randomness-with-linuxs-random-number-generator Cloudflare]

	[https://tools.ietf.org/html/rfc4086 RFC 4086 - Randomness Requirements for Security]		[https://tools.ietf.org/html/rfc4086 RFC 4086 - Randomness Requirements for Security]
Line 138:		Line 138:
	[https://calomel.org/entropy_random_number_generators.html calomel.org]		[https://calomel.org/entropy_random_number_generators.html calomel.org]

	[~~http~~://www.av8n.com/turbid/paper/turbid.htm Turbid]		[https://www.av8n.com/turbid/paper/turbid.htm Turbid]

	[~~http~~://blog.cryptographyengineering.com/2012/02/random-number-generation-illustrated~~.html~~ Random number generation: An illustrated primer]		[https://blog.cryptographyengineering.com/2012/02/21/random-number-generation-illustrated/ Random number generation: An illustrated primer]

	[https://factorable.net/weakkeys12.extended.pdf Mining Your Ps and Qs: Detection of Widespread Weak Keys in Network Devices, PDF]		[https://factorable.net/weakkeys12.extended.pdf Mining Your Ps and Qs: Detection of Widespread Weak Keys in Network Devices, PDF]

	[http://www.pinkas.net/PAPERS/gpr06.pdf Analysis of the Linux Random Number Generator, PDF]		[http://www.pinkas.net/PAPERS/gpr06.pdf Analysis of the Linux Random Number Generator, PDF]{{insecure url\|Connection refused on HTTPS}}

	[~~http~~://cryptome.org/2014/03/eat-entropy-have-it.pdf How to Eat Your Entropy and Have it Too — Optimal Recovery Strategies for Compromised RNGs, PDF]		[https://cryptome.org/2014/03/eat-entropy-have-it.pdf How to Eat Your Entropy and Have it Too — Optimal Recovery Strategies for Compromised RNGs, PDF]

	[~~http~~://eprint.iacr.org/2013/338.pdf Security Analysis of Pseudo-Random Number Generators with Input: /dev/random is not Robust, PDF]		[https://eprint.iacr.org/2013/338.pdf Security Analysis of Pseudo-Random Number Generators with Input: /dev/random is not Robust, PDF]

	[[Category:Server]]		[[Category:Server]]

← Older revision		Revision as of 06:33, 29 July 2023
Line 7:		Line 7:
	* Generation of cryptographic keys		* Generation of cryptographic keys

	* Address Space Layout Randomisation ([~~http~~://en.wikipedia.org/wiki/~~PaX~~#Address_space_layout_randomization ASLR]) - used by default in Alpine of course ;)		* Address Space Layout Randomisation ([https://en.wikipedia.org/wiki/Executable-space_protection#Address_space_layout_randomization ASLR]) - used by default in Alpine of course ;)

	* TCP port randomisation ([https://en.wikipedia.org/wiki/Network_address_translation NAT], outbound connection)		* TCP port randomisation ([https://en.wikipedia.org/wiki/Network_address_translation NAT], outbound connection)
Line 26:		Line 26:

	On a standard system the limit is 4096 bits (512 bytes). The [https://grsecurity.net/ gr-sec] patch used on Alpine increases this limit to 16384 bits (2048 bytes).		On a standard system the limit is 4096 bits (512 bytes). The [https://grsecurity.net/ gr-sec] patch used on Alpine increases this limit to 16384 bits (2048 bytes).
	Entropy is added to the pool in bits from various sources, "the relative number of unknown bits per event is roughly 8/keyboard, 12/mouse, 3/disk, 4/interrupt" [~~http~~://www.issihosts.com/haveged/history.html#intro source] meaning that on a headless server (without mouse and keyboard attached), which ironically is often a system requiring the most entropy, entropy generation is somewhat limited.		Entropy is added to the pool in bits from various sources, "the relative number of unknown bits per event is roughly 8/keyboard, 12/mouse, 3/disk, 4/interrupt" [https://www.issihosts.com/haveged/history.html#intro source] meaning that on a headless server (without mouse and keyboard attached), which ironically is often a system requiring the most entropy, entropy generation is somewhat limited.

	The entropy from the pool can be accessed in two ways by default:		The entropy from the pool can be accessed in two ways by default:
Line 32:		Line 32:
	'''/dev/random''' - On Kernels older than 5.6, this is a [https://en.wikipedia.org/wiki/Blocking_%28computing%29 blocking] resource, so it will use available entropy from the pool. If more entropy is required than is available, the process will wait until more entropy is available in the pool. Due to this behaviour, /dev/random is best used where small amounts of high quality randomness are required, such as for cryptographic keys.		'''/dev/random''' - On Kernels older than 5.6, this is a [https://en.wikipedia.org/wiki/Blocking_%28computing%29 blocking] resource, so it will use available entropy from the pool. If more entropy is required than is available, the process will wait until more entropy is available in the pool. Due to this behaviour, /dev/random is best used where small amounts of high quality randomness are required, such as for cryptographic keys.

	'''/dev/urandom''' - Is a non-blocking resource on all Kernel versions. It uses a seed value from the same entropy pool as /dev/random and therefore, if little entropy is available in the pool, it is recommended not to use /dev/urandom until more entropy is made available in the pool. It runs the seed value through an algorithm and so is a [~~http~~://en.wikipedia.org/wiki/Pseudo-random_number_generator pseudo-random number generator], operating much faster than /dev/random. /dev/urandom is best used for non-cryptographic purposes such as overwriting disks.		'''/dev/urandom''' - Is a non-blocking resource on all Kernel versions. It uses a seed value from the same entropy pool as /dev/random and therefore, if little entropy is available in the pool, it is recommended not to use /dev/urandom until more entropy is made available in the pool. It runs the seed value through an algorithm and so is a [https://en.wikipedia.org/wiki/Pseudo-random_number_generator pseudo-random number generator], operating much faster than /dev/random. /dev/urandom is best used for non-cryptographic purposes such as overwriting disks.

	Writing to /dev/random or /dev/urandom will update the entropy pool with the data written, but this will not result in a higher entropy count. This means that it will impact the contents read from both files, but it will not make reads from /dev/random faster.		Writing to /dev/random or /dev/urandom will update the entropy pool with the data written, but this will not result in a higher entropy count. This means that it will impact the contents read from both files, but it will not make reads from /dev/random faster.
	For more information see the [~~http~~://linux.die.net/man/4/random random manpage]		For more information see the [https://linux.die.net/man/4/random random manpage]

	It is generally recommended wherever entropy is used heavily to supply additional entropy sources; some possibilities are below. Adding more sources of entropy to feed into the pool is a good idea. It makes an attackers job more difficult, because there will be more sources they have to gain control over (or at the very least observe at source), and adding more sources of entropy, even weak ones, can only result in higher entropy.		It is generally recommended wherever entropy is used heavily to supply additional entropy sources; some possibilities are below. Adding more sources of entropy to feed into the pool is a good idea. It makes an attackers job more difficult, because there will be more sources they have to gain control over (or at the very least observe at source), and adding more sources of entropy, even weak ones, can only result in higher entropy.