[HN Gopher] Where does my computer get the time from?
___________________________________________________________________
Where does my computer get the time from?
Author : fanf2
Score : 545 points
Date : 2023-10-05 13:42 UTC (9 hours ago)
(HTM) web link (dotat.at)
(TXT) w3m dump (dotat.at)
| The_suffocated wrote:
| Most of those slides concern about the physics part of time
| measurement (GPS and atomic clock, etc.). While this is
| interesting in its own right, in order to understand how MY
| computer obtains the current time, a more relevant question is
| "how does a home computer measure the latency of a packet sent
| from a remote time server"? Does it measure the durations of
| several roundtrips and take the average duration as latency? What
| if congestion suddenly occurs during some roundtrip? I always
| think that these questions are more mysterious than the physical
| ones.
| tux3 wrote:
| Here's how that works:
|
| https://en.wikipedia.org/wiki/Network_Time_Protocol#Clock_sy...
| TacticalCoder wrote:
| What's amazing is that if your computer is _not_ set to
| automatically sync its time, you can see how fast it 's drifting.
|
| My main desktop is 1.7 seconds ahead at the moment. Probably
| haven't updated the clock in a few weeks: which isn't that much.
| Other systems shall drift much more.
|
| As to "why" it's not setting the time using NTP automatically:
| maybe I like to see how quickly it drifts, maybe I want as little
| services running as possible, maybe I've got an ethernet switch
| right in front of me which better not blink too much, maybe I
| like to be reminded of what "breaks" once the clocks drifts too
| much, maybe I want to actually reflect at the marvel of atomic
| drift when I "manually" update it, etc. Basically the "why" is
| answered by: _" because I want it that way"_.
|
| Anyway: many computer's internal clock/crystal/whatever-
| thinggamagic are not precise at all.
| harikb wrote:
| From wikipedia
|
| > Typical crystal RTC accuracy specifications are from +-100 to
| +-20 parts per million (8.6 to 1.7 seconds per day), but
| temperature-compensated RTC ICs are available accurate to less
| than 5 parts per million.[12][13] In practical terms, this is
| good enough to perform celestial navigation, the classic task
| of a chronometer. In 2011, chip-scale atomic clocks became
| available. Although vastly more expensive and power-hungry (120
| mW vs. <1 mW), they keep time within 50 parts per trillion.
| peteey wrote:
| Crystal errors tend to be around 20 ppm (parts per million)
|
| After a week, 20 ppm would drift 12 * 10^-6 * 7 * 24 * 60 *60 =
| 12 seconds.
|
| Your motherboard probably has a cr2032 keeping it powered when
| unplugged.
|
| Crystals:
| https://www.digikey.com/en/products/filter/crystals/171?s=N4...
| throw0101a wrote:
| > _After a week, 20 ppm would drift 12 * 10^-6 * 7 * 24 * 60
| *60 = 12 seconds._
|
| Where are you getting that 12 from?
| crote wrote:
| It kinda makes you wonder why desktop computers don't use the
| AC frequency as a stable-ish time source. Short-term accuracy
| is pretty poor, but it can definitely do better than 12
| seconds over a week!
| moffkalast wrote:
| I suppose it's because no AC ever gets to the motherboard
| in your typical ATX setup? It's all just DC 12/5/3 volts
| and could be coming from a battery for all it knows. There
| would need to be an optional standard way of getting time
| from the PSU and have the AC time keeping there.
| crote wrote:
| Of course, but there's no reason why a 50/60Hz signal
| couldn't have been included in the ATX power connector
| back when it was established a few decades ago.
|
| In an alternate universe it would've been put in there,
| together with all the weird -12V / -5V rails nobody uses
| these days. Getting it these days would indeed be pretty
| much impossible.
| fanf2 wrote:
| There's a fun thing about quartz wristwatches: one of the
| biggest contributions to frequency fluctuations in a quartz
| oscillator is temperature. But if it is strapped to your
| wrist, it is coupled to your body's temperature homeostasis.
| So a quartz watch can easily be more accurate than a quartz
| clock!
|
| Really good watches allow you to adjust their rate, so if it
| runs slightly fast or slow at your wrist temperature, you can
| correct it.
|
| One of the key insights of John Harrison, who won the
| Longitude prize, was that it doesn't matter so much if a
| clock runs slightly fast or slightly slow, so long as it
| ticks at a very steady rate. Then you can characterise its
| frequency offset, and use that as a correction factor to get
| the correct GMT after weeks at sea.
| lxgr wrote:
| That would require tuning it to the average body
| temperature though, right?
|
| Or are you saying that what makes quartz crystals drift is
| the change in temperature?
| fanf2 wrote:
| Both are true :-)
| koito17 wrote:
| When setting up a mini PC as a home server about 40 days ago, I
| did not realize Fedora Server does not configure NTP
| synchronization by default. In only two weeks I managed to
| accumulate 30 seconds worth of drift. Prometheus was
| complaining about it but I had erroneously guessed that the
| drift alert was due to having everything on a single node. Then
| when querying metrics and seeing the drift cause errors, I
| compared the output of date +'%s' on the server and my own
| laptop. The difference was well over 30 seconds.
| ReactiveJelly wrote:
| Can't say too much but I saw an IoT product where, if NTP
| failed, they would all slowly fall behind. I really appreciated
| this because fixing NTP would jump forward, leaving a gap in
| perceived time instead of living the same moment twice.
|
| So I assumed that, like how speedometers purposely read a
| little high, the crystals must purposely read a little slow so
| that computers don't slip into the future.
| b8 wrote:
| Is there a way to get time to be 99% or 100% accurate? time.gov
| shows that my Win11 and Android Pixel are off by almost a second.
| It'd be cool if it could grab it from the atomic clock.
| LeoPanthera wrote:
| I think this is a quirk of Windows and Android machines, which
| do not aim for perfect precision.
|
| macOS is generally accurate to less than a tenth of a second
| (assuming desktops - laptops maybe less so, as they sleep a
| lot), and Linux will be just as accurate as long as it is
| running ntpd and not systemd-timesyncd.
| zokier wrote:
| 99% accurate is pretty vague, but in terms of timekeeping 1% of
| 24 hours is still almost 15 minutes so being off by a second is
| couple of orders of magnitude better. Just to give some
| perspective.
|
| NTP definitely should be able to keep the clock correct to sub-
| second level, but for more accurate local clock something like
| Open Time Card would do the trick, it has local atomic clock
| together with GPS receiver to get pretty much reference quality
| time.
| crote wrote:
| Install a GPS module in your computer.
|
| Your Android phone is already capable of receiving GPS, so
| that's probably the most readily-available accurate time
| source. Getting your Android phone to _sync_ to GPS time
| instead of just displaying it in an app might be a bit tricky,
| though...
| tbm57 wrote:
| I think we need a community-maintained and democratized time-
| tracking standard so we're not so beholden to Big Time
| callalex wrote:
| Put it on the clockchain
| urbandw311er wrote:
| Please tell me you just coined this.
| [deleted]
| huehehue wrote:
| The article, and this comment, makes me wonder what impact a
| coordinated attack on the root time-keeping mechanisms might
| have. It seems like there's a fair bit of redundancy /
| consensus, but what systems would fail? On what timeline? How
| would they recover?
| crote wrote:
| That's pretty much what we already have, isn't it?
|
| True Time(tm) is determined by essentially averaging dozens of
| atomic clocks from laboratories all over the world. It doesn't
| really get any more "community-maintained" and "democratized"
| than that!
| nektro wrote:
| we're not, it's run by the government
| kristopolous wrote:
| It's probably possible to calibrate your clock using a clear
| night sky and a modern cell phone camera. I bet second accuracy
| isn't an absurd expectation. Now it'd probably take an
| unreasonable amount of time to calibrate...
| rantee wrote:
| Great overview, thanks for sharing. Maybe this was unintentional,
| but I got a good laugh out of, "In 1952, the International
| Astronomical Union changed the definition of time"!
| adenner wrote:
| This reminds me of a talk I gave several years ago to my local
| linux users group (CIALUG) about time... I don't have the
| recording anymore but still have the slides
| https://www.slideshare.net/denner1/all-about-time-or-how-to-...
| fckgw wrote:
| Just want to take a moment to appreciate the URL of "dot at, dot
| at, slash at"
| FireBeyond wrote:
| IIRC there was an ISP or web host in Australia way back in the
| day called DotNet (obviously before the MSFT days)...
|
| Their website was http://www.dotnet.net.au (www dot dotnet dot
| net dot au).
| firatt wrote:
| you should see the email address of the author :)
| nayuki wrote:
| Definitely reminds me of H T T P colon slash slash slashdot dot
| org
| alch- wrote:
| Oooooh decades later I finally get the name Slashdot! Thank
| you!
| auspiv wrote:
| If you have a Raspberry Pi laying around and want to run your own
| Stratum 1 NTP server -
| https://austinsnerdythings.com/2021/04/19/microsecond-accura...
| fanf2 wrote:
| Note that for NTP it's better to use a Raspberry Pi 4 than
| older boards. The old ones have their ethernet port on the
| wrong side of a USB hub, so their network suffers from
| millisecond-level packet timing jitter. You will not be able to
| get microsecond-level NTP accuracy.
|
| For added fun, you can turn the Raspberry Pi into an oven
| compensated crystal oscillator (ocxo) by putting it in an
| insulated box and running a CPU burner to keep it toasty.
| https://blog.ntpsec.org/2017/03/21/More_Heat.html (infohazard
| warning: ntpsec contains traces of ESR)
| gentleman11 wrote:
| Where does my car get the time from? It drifts and changes every
| time I start it up. Every 3 months I have to change it manually
| by 10ish minutes or more, but it's inconsistent
| spelunker wrote:
| I have the same problem! It takes months, but eventually the
| clock in my car is minutes behind. I think currently it's about
| 4 minutes behind.
| SAI_Peregrinus wrote:
| Probably just a local quartz oscillator, like a cheap
| wristwatch but embedded into the car. That'll drift with
| temperature, vibration, humidity, and some other factors, but
| it's cheap and just relies on the user to occasionally set it.
| Fancier systems can use radio time or GNSS (more likely if the
| car has built in navigation), but that's probably not happening
| if you regularly set the time!
| CableNinja wrote:
| Correct. Oscillators are subject to drift through a number of
| means, and they all have ridiculous effects too.
| https://news.ycombinator.com/item?id=37613523
| jrockway wrote:
| Temperature is the largest factor. Things like a DS3231[1]
| do really well compared to a basic non-compensated
| oscillator. I have been running some long-term experiments
| on a few that I have around and with some tuning got them
| to less than a second loss per year. But, they are super
| expensive compared to the basic ones (almost $5 each in
| quantity), so they aren't going to end up in your car where
| a 3 cent chip is possible to use instead. (I don't know
| what 5G / LTE chips cost these days, but if they're putting
| one in your car anyway, then they can probably get the time
| from that. But choose not to.)
|
| [1] https://www.analog.com/media/en/technical-
| documentation/data...
|
| Most interesting to me in all of my time experiments is
| looking at my clock frequency over time vs. the
| temperature. (NTP daemons aim to calculate your actual
| clock frequency; then they know how far off your internal
| time is from actual time.) You don't even need a
| temperature sensor, the clock rate is a perfect analogue.
| lazide wrote:
| Voltage issues can also be a big problem, and cars have
| notoriously dirty electrical.
| jrockway wrote:
| Ahh, I bet that's true!
| crote wrote:
| > A company i worked for wanted systems to have no more
| than 2ns of time drift between each other, in a network of
| +10 devices.
|
| At that point it's surprising they didn't just deploy a
| local "time network", with a single master clock
| distributing time via length-calibrated coax. Approaches
| like that are really common in television studios.
| CableNinja wrote:
| It wasnt really the right environment for it, and they
| didnt even actually need that high of resolution, they
| couldve gotten away with 100ms drift and never noticed
| willis936 wrote:
| It sounds like it gets the time from you.
| fuzzfactor wrote:
| Laurens Hammond invented the synchronous electric motor once
| A/C domestic voltage had proliferated enough as an
| alternative to the original D/C electrification first
| established by Edison.
|
| This made it possible for the first time to build clocks
| based on the stable frequency of the incoming A/C supply
| voltage, much more reliably than those based on the incoming
| line voltage, which varies quite a bit whether it is A/C or
| D/C.
|
| This put him on the map as a manufacturer when he went
| forward to build Hammond clocks commercially.
|
| Years later his engineers encouraged him to consider
| developing an electric church organ, which would be possible
| to remain in tune regardless of variations in line voltage
| themselves.
|
| Hammond was not musically inclined but he did it anyway.
|
| Right up there with the Great Men in the most legendary way.
|
| http://thehammondorganstory.com/
|
| By the time the 1960's came around, almost all new American
| vehicles were recognized as modern Space Age conveniences,
| and a factory clock (mechanical analog, naturally) had become
| almost a universal standard accessory beyond the most budget
| price points.
|
| There were a couple drawbacks to the factory clocks, they had
| to be connected to the car battery at all times to keep
| running, they didn't drain the battery very much at all but
| still would eventually deaden it if undriven, way worse than
| no clock. And they depended on the incoming voltage which
| determined the internal clock motor speed to begin with.
| Different automotive electrical systems and batteries
| themselves do vary perhaps 10 percent about a nominal design
| voltage of 12 VDC. There is no stable A/C in the car that a
| synchronous motor would need to run on[0].
|
| These now-vintage clocks were self-correcting. You correct
| them yourself. Actually the same twisting of the knob to move
| the hands of the clock, which was familiar from earlier non-
| correcting clocks simply did the job. So they were somewhat
| backward-compatible. Only the Space Age units had smart
| enough mechanical ability to take into account how much and
| in which direction you moved the hands, and adjusted the
| previous running speed accordingly. If the clock was not very
| close to correct time when you adjusted it, it would take
| repeated adjustments over a number of days or weeks to get it
| to very realistic speed. All it really did was successive
| approximation. You had to supply your own natural
| intelligence.
|
| Even at the time lots of drivers never knew this, and there
| was widespread disappointment over the wildly inaccurate
| clocks "which were OK when new but went downhill 'through
| time'". They only added maybe a dollar to your car payment
| but that was very expensive compared to a highly reliable
| cheap household clock at the time.
|
| When you think about it, today lots of drivers are not quite
| up to par when it comes to engaging the amount of natural
| intelligence that would be needed in many other ways besides
| timekeeping.
|
| [0] The electrical "vibrator" which provided switch-mode
| 12VAC which could be stepped up by a transformer to supply
| much higher voltage to power vacuum tube radios still
| produced a variable A/C voltage & frequency, dependent on the
| underlying D/C supply voltage.
| linkjuice4all wrote:
| The clock in my 1967 Mercury has an interesting mechanism.
| It's a fully mechanical wound spring clock with a self-
| winding mechanism. When the spring unwinds it closes a
| circuit on an electromagnet that quickly rewinds the clock
| spring.
|
| Every couple of hours or so you'll hear the click from it
| rewinding on its own. Unfortunately there's nothing to
| prevent it from running down the battery and they often
| need to be replaced due to burn out when the voltage gets
| low. Essentially the rewinder doesn't have enough voltage
| to actually wind the clock and the circuit stays closed.
| fuzzfactor wrote:
| Nothing like a '60's Mercury when they were still
| building them more carefully than the corresponding
| mainstream Ford-badged models.
|
| >Well if I had money
|
| >Tell you what I'd do
|
| >I'd go downtown and buy a Mercury or two
|
| Mercury Blues:
|
| https://www.youtube.com/watch?v=QsTfCITzISM
|
| I could really use a Mercury or two about now myself.
| CableNinja wrote:
| Here, have a rabbithole.
| https://news.ycombinator.com/item?id=37613523
| paxys wrote:
| I recently rented a $65000 luxury car and it didn't even have
| built-in daylight savings adjustment. Owners have to dig into
| settings and fix it themselves twice a year. Cars are so far
| behind on basic software it is crazy.
| ipython wrote:
| Oh, it gets better. I used to get reminders in the mail to
| take my luxury car into the dealership for "service" to
| adjust the clock twice a year. Or I could ... you know, just
| press a few buttons for free.
|
| The trouble with all the modern cars that have synchronized
| clocks is that, well, you've already put in an LTE SIM card,
| so why not send up some telemetry at the same time? And here
| we are, with cars that are surveillance devices with four
| wheels.
| reaperman wrote:
| A simple GPS receiver could also provide the time. But I
| agree with your rant overall.
| incanus77 wrote:
| What really gets me is when the gauge cluster clock and the
| radio clock differ. Just a wonderful metaphor for the modern
| car.
| lm28469 wrote:
| Depends on the car model. Some can use GPS or radio time
| signals: https://en.wikipedia.org/wiki/Time_signal
| binbag wrote:
| "the BIPM collects time measurements from national timing
| laboratories around the world"
|
| I'm really interested in how this is done with multiple clocks
| over a distance. Can anyone explain? It feels like it would be
| very difficult since asking "what time is it there?" at the
| timescale of atomic clocks is kind of a bit meaningless? And
| that's before considering the absolute local nature of time and
| the impossibility of a general universal time per relativity.
| fanf2 wrote:
| The term of art you want for searchengineering is "time
| transfer".
|
| There are a variety of mechanisms:
|
| * fibre links when the labs are close enough
|
| * two-way satellite time transfer, when they are further apart
|
| * in the past, literally carrying an atomic clock from A to B
| (they had to ask the pilot for precise details of the flight so
| that they could integrate relativistic effects of the speed and
| height)
|
| * there's an example in the talk, of how Essen and Markowitz
| compared their measurements by using a shared reference, the
| WWV time signal.
| crote wrote:
| I believe an important aspect is that the _actual_ time offset
| between the clocks doesn 't matter all that much - it is the
| drift between them you care about.
|
| True UTC is essentially an arbitrary value. Syncing up with
| multiple clocks is done to account for a single clock being a
| bit slow or fast. It doesn't matter if the clock you are
| syncing with is 1.34ms behind, as long as it is _always_ 1.34ms
| behind. If it 's suddenly 1.35ms behind, there's 0.01ms of
| drift between them and you have to correct for that. And if
| that 1.34ms-going-to-1.35ms is _actually_ 1.47ms-going-
| to-1.48ms, the outcome will be exactly the same.
|
| This means you could sync up using a simple long-range radio
| signal. As long as the time between transmission and reception
| for each clock stays constant, it is pretty trivial to
| determine clock drift. Something like the DCF77 and WWVB
| transmitters seems like a reasonable choice - provided you are
| able to deal with occasional bounces off the ionosphere.
|
| Of course these days you'd probably just have all the
| individual clocks somehow reference GPS. It's globally
| available, after all.
| fanf2 wrote:
| It isn't _just_ the difference in rate. The main content of
| Circular T https://www.bipm.org/en/time-ftp/circular-t is the
| time offset of the various national realisations of UTC.
| Another important aspect is characterizing the stability of
| each clock, which determines the weighting of its
| contribution to UTC.
|
| The algorithm behind Circular T is called ALGOS.
| perihelions wrote:
| /Meta: There's three different posts on the front page on the
| theme of "what is time, anyway", and I'm curious if there some
| reason for that? Did I miss some news event? Did some leap-second
| bug crash something?
| wwalexander wrote:
| I'll often see articles on the front page related to a popular
| thread from a day or two ago. I always assume that someone
| either went down a rabbit hole based on the original thread and
| wanted to share their findings, or already knew about that
| topic and felt inspired by the original thread to share
| something useful about it.
| pbhjpbhj wrote:
| Hypothesis:
|
| People gaming clicks using popularity of subjects from past
| years would want to drift (heh!) the time forward slightly,
| these topics probably normally arise around the time clocks
| change for Winter (29 October this year is the end of British
| Summer Time). So, I speculate that this is a drifted "clocks go
| back, but will your computer adjust itself?" topic area.
| iamnotsure wrote:
| https://girard.perso.math.cnrs.fr/mustard/article.html
| waterheater wrote:
| Related to timekeeping is the NIST Randomness Beacon:
| https://csrc.nist.gov/projects/interoperable-randomness-beac...
|
| "This prototype implementation generates full-entropy bit-strings
| and posts them in blocks of 512 bits every 60 seconds. Each such
| value is sequence-numbered, time-stamped and signed, and includes
| the hash of the previous value to chain the sequence of values
| together and prevent even the source to retroactively change an
| output package without being detected."
|
| People here were joking about putting time on the blockchain,
| and, well, NIST is already doing it.
| eternityforest wrote:
| I always wondered why nobody is using that as the root of a P2P
| randomness system.
|
| It would be very useful to have a trusted source of time, with
| a few keys that are meant to never change, that anyone can
| rebroadcast.
|
| We could have zero configuration clocks that get the time from
| the nearest phone or computer without any manual setup!
| sandpaper26 wrote:
| Can someone give an example use case of this? I'm not sure I
| understand why a very public long string of random characters
| on a block chain is useful, except as a way to prove an event
| didn't happen prior to a certain time
| fanf2 wrote:
| See https://news.ycombinator.com/item?id=37783764
| nonameiguess wrote:
| The draft of the version upgrade explains the possible uses
| of this: https://nvlpubs.nist.gov/nistpubs/ir/2019/NIST.IR.82
| 13-draft...
|
| Mostly, it's so the public can verify events that were
| supposed to be random really were random. The executive
| summary gives plenty of examples, but think of a pro sports
| draft lottery. Fans always think those are rigged. They could
| simply use these outputs and a hashing function that maps a
| 512-bit block to some set with cardinality equal to the
| number of slots and pre-assign slots to participating teams
| based on their draft weight. Then fans could verify using
| this public API that the draw the league claims came up
| randomly really did come up randomly.
|
| People always think polls are rigged. This could be used to
| publicly produce random population samples for polling.
|
| This was also used to prove a Bell inequality experiment
| worked with no loopholes.
| codetrotter wrote:
| If they want to believe the polls are rigged, won't they
| just assume that the NIST random data is "rigged" as well.
| throwaway89201 wrote:
| > People here were joking about putting time on the blockchain,
| and, well, NIST is already doing it.
|
| It's not a blockchain, but a single writer Merkle DAG. No
| consensus necessary. Much like a git repository with a single
| author.
| waterheater wrote:
| >It's not a blockchain, but a single writer Merkle DAG.
|
| Hmm. Just because something's a Merkle DAG doesn't make it
| useable on the Internet. A single-writer blockchain, perhaps?
| SV_BubbleTime wrote:
| Oh... so you are calling a database a "block chain".
| r3trohack3r wrote:
| A blockchain is a chain of blocks.
|
| Do you have another definition?
|
| Colloquially, it often refers to a consensus algorithm
| paired with a chain of blocks.
|
| Bitcoin's innovation wasn't a blockchain, it was a proof-
| of-work backed consensus algorithm that allowed a group of
| adversarial peers to agree on the state of a shared
| blockchain datastructure.
| waterheater wrote:
| According to the dictionary [1], a blockchain is "a
| digital database containing information (such as records
| of financial transactions) that can be simultaneously
| used and shared within a large decentralized, publicly
| accessible network"
|
| The distinction here might be with a decentralized
| network.
|
| [1] https://www.merriam-webster.com/dictionary/blockchain
| ipaddr wrote:
| Merriam is incorrect
| r3trohack3r wrote:
| People keep saying Merkle DAGs when someone calls a linear
| chain of recursively hashed data blocks a blockchain.
|
| I don't understand.
|
| My understanding of the Merkle Tree is that it's a recursive
| hash, but the leaf nodes are the data, each layer up the tree
| is the hash of the child nodes.
|
| In a merkle tree, only the leaf nodes store (or reference)
| data, everything else is just a hash.
|
| Is there another merkle structure I don't know about?
|
| https://en.wikipedia.org/wiki/Merkle_tree
|
| If the nodes with hashes contain data, it's not a merkle
| tree.
| tedunangst wrote:
| I think this is isomorphic to an unbalanced tree where
| every node has one non leaf child and one leaf child.
| r3trohack3r wrote:
| Seems like claiming that a linked list isn't actually a
| linked list it's an unbalanced tree where every node has
| one child node.
|
| I mean, you're not wrong but it's still a linked list.
|
| I'd be careful muddying up your mental models this way
| though - they're distinct data structures for distinct
| purposes.
|
| You would likely not want to use a merkle tree for an
| append only log, and likely would not want to use a
| blockchain for verifying file integrity.
|
| For example, BitTorrent, IPFS, and Storj use merkle trees
| to verify and discover blocks on the DHT, you would not
| want to use a blockchain for this.
|
| And Scuttlebutt uses a blockchain as an append only log
| that is gossip friendly, you would not want to use a
| merkle tree for this.
| zzo38computer wrote:
| If each block contains the hash of the previous block, then I
| think that it is a blockchain (regardless of if there is
| multiple authors or only a single author). A git repository
| is a blockchain, too.
| zeusk wrote:
| Would you know! So Linus is the real father of blockchain?
| CobrastanJorji wrote:
| Wikipedia suggests that David Chaum first proposed what
| was basically a blockchain in 1982. He even had a crypto
| startup way before they were cool, with "eCash" in 1995.
| waterheater wrote:
| According to a news article, the first blockchain
| application is an application released in 1992 called
| AbsoluteProof by the company Surety [1].
|
| [1] https://www.vice.com/en/article/j5nzx4/what-was-the-
| first-bl...
| fanf2 wrote:
| Yay, _thank_ you, I was racking my brains trying to
| remember Surety as an example in response to
| https://news.ycombinator.com/item?id=37782446
| 1vuio0pswjnm7 wrote:
| "As Ethereum's cofounder Vitalik Buterin joked on
| Twitter, if someone wanted to compromise Surety's
| blockchain they could "make fake newspapers with a
| different chain of hashes and circulate them more
| widely." Given that the New York Times has an average
| daily print circulation of about 570,000 copies, this
| would probably be the stunt of the century."
|
| What if the hash is published in multiple newspapers.
| throw0101a wrote:
| > _If each block contains the hash of the previous block,
| then I think that it is a blockchain_ [...]
|
| Or simply a 'hash chain':
|
| > _A hash chain is similar to a blockchain, as they both
| utilize a cryptographic hash function for creating a link
| between two nodes. However, a blockchain (as used by
| Bitcoin and related systems) is generally intended to
| support distributed agreement around a public ledger
| (data), and incorporates a set of rules for encapsulation
| of data and associated data permissions._
|
| * https://en.wikipedia.org/wiki/Hash_chain
|
| Or perhaps:
|
| > _Linked timestamping creates time-stamp tokens which are
| dependent on each other, entangled in some authenticated
| data structure. Later modification of the issued time-
| stamps would invalidate this structure. The temporal order
| of issued time-stamps is also protected by this data
| structure, making backdating of the issued time-stamps
| impossible, even by the issuing server itself._
|
| * https://en.wikipedia.org/wiki/Linked_timestamping
|
| An(other) example of the latter: This
| document describes a mechanism, called syslog-sign in this
| document, that adds origin authentication, message
| integrity, replay resistance, message sequencing,
| and detection of missing messages to syslog.
| Essentially, this is accomplished by sending a special
| syslog message. The content of this syslog message is
| called a Signature Block. Each Signature Block
| contains, in effect, a detached signature on some
| number of previously sent messages. It is
| cryptographically signed and contains the hashes of
| previously sent syslog messages. The originator of
| syslog-sign messages is simply referred to as a
| "signer". The signer can be the same originator as
| the originator whose messages it signs, or it can be a
| separate originator.
|
| * https://datatracker.ietf.org/doc/html/rfc5848
| m3kw9 wrote:
| Ok but then anyone in control can change the entire tree, why
| need this Merkle tree?
| donalhunt wrote:
| DARPA are funding the Robust Optical Clock Network (ROCkN)
| program, which aims to create optical atomic clocks with low
| size, weight, and power (SWaP) that yield timing accuracy and
| holdover better than GPS atomic clocks and can be used outside a
| laboratory.
|
| Most of the big cloud providers have deployed the equivalent of
| the opencompute time card which sources its time from GPS sources
| but can maintain accurate time in cases of GPS unavailability.
|
| https://www.darpa.mil/news-events/2022-01-20
| kilbuz wrote:
| every NTP story needs a link to the Netgear/UW-Madison fiasco:
| https://pages.cs.wisc.edu/~plonka/netgear-sntp/
| fanf2 wrote:
| And PHK / D-Link https://en.m.wikipedia.org/wiki/Poul-
| Henning_Kamp#Dispute_wi...
| cmurf wrote:
| Are smartphones using GPS for time, or NTP?
| adrianmonk wrote:
| I'm pretty sure the cell network itself can provide time. Not
| sure if smartphones use it.
|
| I think older cell phones that didn't have GPS or a data plan
| (voice only) did use it. ~15 years ago, I had an old flip phone
| that had an option to set the time manually or automatically,
| and T-Mobile "helpfully" provide a time source that was like 5
| minutes slow.
| fanf2 wrote:
| The time reference inside a cell tower is usually PTP
| ThinkingGuy wrote:
| Yes :)
| tiffanyh wrote:
| TL;DR;
|
| The flow of how _modern day_ time is sourced & relayed to your
| computer:
|
| 1. Based on quantum / atom movement -> units -> time
|
| 2. Atomic clock based on #1
|
| 3. Time from #2, relayed to US Naval Observatory Alternate Master
| Clock
|
| 4. Time from #3, relayed to Space Force Base
|
| 5. Time from #4, relayed to GPS
|
| 6. Time from #5, relayed to NTP
|
| 7. Time from #6, relayed to your home computer
| gandalfian wrote:
| It used to irritate me that my old dumb mobile must have known
| exactly the correct time in order to operate on the cell phone
| network. Yet it kept it secret from me. I had to manually set the
| clock by guesstimate
| callalex wrote:
| In the early days of mobile networks, it was my experience that
| the network time was not very good. Sometimes off by a minute
| or two, but most often filled with DST bugs.
| freedude wrote:
| Just be careful which time source you use. One of our servers was
| configured to use tick.usno.navy.mil and tock.usno.navy.mil back
| 10-15 years ago or so. The Navy had an "issue" with the time they
| were sending out. The overnight result was several licensing
| servers wouldn't authenticate and we were locked out of those
| systems(SSH needs accurate time, within minutes I believe). We
| discovered the discrepancy by logging in locally (we were in the
| same building but a different office) and changed the time
| servers and then the sync method to resolve the issue.
| bityard wrote:
| > SSH needs accurate time, within minutes I believe
|
| You may be mis-remembering a few details, SSH does not care
| about the time at all unless you are using _very_ short-lived
| SSH certificates.
| fanf2 wrote:
| They might have been using kerberos authentication?
| xorcist wrote:
| Kerberos is very particular about time.
| freedude wrote:
| This system operated an SMB share so Kerberos is probably
| what locked us out.
| lazide wrote:
| Time based OTP is pretty sensitive though. Probably that is
| what broke?
| crote wrote:
| The irony is that the TOTP spec explicitly takes this into
| account.
|
| By default tokens are valid for 30 seconds, with a token
| from the _previous_ 30-second window also being accepted.
| Being off by more than that is pretty rare for NTP-
| connected systems.
|
| The specs also provide ways to deal with a dedicated
| hardware token slowly going out of sync by keeping track of
| the last-known clock drift, but that's pretty useless these
| days and can even do more harm than good.
| lazide wrote:
| The poster was referring to minutes, which has also been
| my experience. Something goes wrong, and suddenly you're
| an hour off. Blam, now you can't login. :s
| freedude wrote:
| You are correct and I believe it was Kerberos that we were
| locked out of on this system since it was running a SMB
| share.
| dghughes wrote:
| My cat is crazy accurate for time down to the minute. I can be
| sitting reading, on the web, or watching a movie all of which are
| random and not repeated at any specific time. Yet at 9pm exactly
| any time of the year she sits by the stool and complains if I am
| not there to give her a treat at 9pm Atlantic time.
|
| Note she does get thrown off by seasonal time changes in the fall
| and spring but she only needs about a week to reset.
| ComputerGuru wrote:
| It's not just cats; I think humans are capable of much of the
| same but we actively suppress it for $reasons.
|
| Any time I have an alarm in the middle of the night for any
| random hh:mm, after just a few days of the same pattern I will
| naturally wake up exactly 1 or 2 minutes before the alarm as my
| internal clock knows what to expect. If I ignore it out of
| laziness and go back to sleep until the alarm rings (literally
| a minute later) I can break the habit but if I embrace it, it
| is really accurate and reliable (though thrown off if I went to
| bed absolutely exhausted, so there are limits as one would
| naturally expect).
| costcofries wrote:
| They are creatures of habit
| miohtama wrote:
| Can my computer get time from your cat? (:
| hinkley wrote:
| Our dogs meanwhile get fed at 5:00 and every day they think it
| must be 5:00 at 4:15-4:25, so it seems my dogs may be Martians.
| Arrath wrote:
| Girlfirend's minpin-chihuahua mix is like this. Thinks its
| breakfast time well before it is, indeed, time for breakfast.
| Jagerbizzle wrote:
| Exactly the same here with my golden doodle. We feed her
| dinner at 4pm and she's pretty much always off-by-one and
| comes to check on the status at 3.
| hinkley wrote:
| Maybe retrievers are bad at time. The ring leader is a lab.
| [deleted]
| stronglikedan wrote:
| My dog knows the days of the week too. She knows that Thursday
| is brewery night, and Sunday is a visit to grandma's. She get
| confusedly persistent if either event is cancelled.
| cj wrote:
| My dog is the same. I have a friend who spends the day at my
| house every Thursday. The dog sits by the door waiting, but
| only on Thursdays!
| fuzzfactor wrote:
| I found out my cat could count to four once every fourth
| day was salmon day.
| geek_at wrote:
| Pawlow would have something to say about that
| diggan wrote:
| Same with my dogs! One of them come and puts her paw on me at
| exactly 20:00 every day, down to the minute as well, to remind
| me that it's foodie time.
|
| Maybe I could use my dog instead of NTP and have her press a
| button that syncs my computers to exactly 20:00? Would work
| offline at least.
| [deleted]
| dghlsakjg wrote:
| That's so interesting. My dog runs on a solar clock. He
| starts begging for his dentastick when it gets dark out, and
| stays in bed until the sun comes up in winter.
| augusto-moura wrote:
| It gives me an idea of training my dog to hit a button to get
| food and eventually plot the data onto a graph. Would be
| funny to draw some patterns from it
| m463 wrote:
| maybe add an NTP reference clock to biff1
|
| ...or add it to systemd (it will get there eventually anyway)
|
| [1] https://en.wikipedia.org/wiki/Biff_(Unix)#Origin_and_name
| mrb wrote:
| Think about the number of pets doing this at, say, 20:07, and
| owners not realizing the time accuracy because it's not a
| round number of minutes after the hour.
| renewiltord wrote:
| There are circadian rhythm genes in c. elegans that take
| effect even when under artificial light. Also the skill for
| this is trainable.
|
| At school we used to have a bell mark class ends and
| without a clock or a watch I could predictably tell when
| the bell would fire. One time I demonstrated this to a
| friend (both of us kicked out of class) by counting down
| from 10 on the second to when the bell rang while looking
| at a blank wall.
|
| Strange. But nonetheless true.
| hellotheretoday wrote:
| We started using an automated feeder with our dog. It broke
| one day and we were surprised to see that he was prompting us
| to feed him almost exactly at the programmed times. Like down
| to the minute.
|
| Not sure if he's relying on other sensory information like
| certain smells or sounds. I don't believe that's the case; we
| didn't replace the broken feeder for 3-4 months and he was
| able to keep time within a few minutes during that period.
| Our behavior is erratic and changes often; we work jobs with
| very inconsistent schedules (thus the automatic feeder) so
| it's likely not that our behavior is prompting him as well.
| We can even observe him consistently going to his feeding
| area on the security camera at the correct time when no one
| is home. Interesting stuff!
| jvanderbot wrote:
| Circadian cycles are pretty reliable in terms of
| timekeeping. I end up upstairs every day for lunch at about
| the same time, and I always find myself in the kitchen
| grabbing a diet coke at about 130 because I used to grab
| one after a 1pm meeting for the longest time.
| hellotheretoday wrote:
| Does that hold true for animals though? Modern humans
| sleep on a pretty consistent schedule but my dog sleeps
| randomly throughout the day. And unfortunately for him my
| sleep schedule is utter chaos so he is often up very late
|
| And to further make it weird: our vet told us to feed him
| multiple small feedings throughout the day so the feeder
| was programmed for 6 feedings with 2 hour intervals from
| 9am to 9pm. He hit the mark for all feeding times!
|
| I still think there is potentially some sort of external
| prompt(s) though. Circadian rhythm is an excellent idea.
| Maybe that combined with something hard to detect, like
| lighting levels (which would explain why the timing
| shifted a few minutes over a few months). Who knows!
| clord wrote:
| I suspect in cases like this the dog is hearing something you
| don't in the environment and has associated it with treat
| time, creating the expectation. If you reconfigure NTP to use
| her intuition, you risk biasing whatever the source is,
| creating a feedback loop that will create drift.
| xkcd-sucks wrote:
| It's written, and seems plausible, that cat territory is
| bounded by time as well as space; for example one cat might own
| a place in the morning while another cat owns the same place in
| the evening, etc.
| qbxk wrote:
| cat law sounds hard. cat lawyers must make a fortune
| litigating in cat court
| [deleted]
| aequitas wrote:
| There was this BBC documentary where they tracked cats with
| GPS called The secret life of cats where they found this
| behavior. The cats would also visit each others house at
| different time and eat from each others food.
| BirAdam wrote:
| My guinea pig will get really really loud and persistent if she
| doesn't get her vitamin c laced hay biscuit at 7AM EST. I have
| no idea how she knows what time it is, but she's super accurate
| about it as well.
| TomK32 wrote:
| Only one? It's recommended to keep at least two as they are
| very social animals.
|
| My four live in the garden, well protected and I'm too
| chaotic to keep any sort of regular feeding schedule, but
| they are fine with that, must be exciting for them if an
| unexpected feed of carrots or cucumbers drops.
| switch007 wrote:
| Their guinea pig may cohabit or socialise with non Guinea
| pigs. Eg rabbits
| glonq wrote:
| I better check the oscillator inside my cats, because they want
| dinner at 4pm plus or minus a half hour.
| jesterpm wrote:
| It's even weirder with people: blood sugar level change with
| how you perceive time to be passing, not the actual amount of
| time: https://www.pnas.org/doi/10.1073/pnas.1603444113
| distract8901 wrote:
| Does anyone have a good explainer for how the NTP protocol works?
| I can't quite wrap my head around how you could possibly
| synchronize two machines in time over a network with unknown and
| unpredictable latency.
| LVB wrote:
| Specifically on the latency question, have a look at
| https://stackoverflow.com/a/18779822 for a basic explanation.
| tldr, once you allow for two-way communication you can start to
| factor out the network delay.
| LeoPanthera wrote:
| NTP uses the "intersection algorithm":
|
| https://en.wikipedia.org/wiki/Intersection_algorithm
| mhh__ wrote:
| It's not quick but "Computer Network Time Synchronization" by
| Mills
| fuzzfactor wrote:
| It's an interesting situation when instruments or measurements
| become more precise, stable, or reliable than the reference
| material.
|
| And when someone (usually an individual) finally discovers that
| it has happened, or in some cases makes it so.
|
| >the ephemeris second is based on an astronomical ephemeris,
| which is a mathematical model of the solar system
|
| >the standard ephemeris was produced by Simon Newcomb in the late
| 1800s >he collected a vast amount of historical astronomical data
| to create his mathematical model >it remained the standard until
| the mid 1980s
|
| >in 1952 the international astronomical union changed the
| definition of time so that instead of being based on the rotation
| of the earth about its axis, it was based on the orbit of the
| earth around the sun >in the 1930s they had discovered that the
| earth's rotation is not perfectly even: it slows down and speeds
| up slightly >clocks were now more precise than the rotation of
| the earth, so the ephemeris second was a new more precise
| standard of time
| darkwater wrote:
| >in 1952 the international astronomical union changed the
| definition of time so that instead of being based on the
| rotation of the earth about its axis, it was based on the orbit
| of the earth around the sun >in the 1930s they had discovered
| that the earth's rotation is not perfectly even: it slows down
| and speeds up slightly
|
| Yeah, I remember studying that back in high school but I
| wonder... what previous actual duration of a second they used?
| And also, being based on the rotation of Earth, what kind of
| data was the "vast amount of historical astronomical data"
| Newcomb collected? How can you reliably capture and store the
| length of time if you can only base it on the Earth rotation
| speed which varies over time? I would guess the data compared
| it to other natural phenomena?
| fanf2 wrote:
| When time was based on earth rotation, astronomers used
| "transit instruments" to observe when certain "clock stars"
| passed directly overhead. The clock stars had accurately
| known positions, so if you routinely record the time they
| pass overhead according to your observatory's clock, then you
| can work out how accurate your clock is.
|
| Newcomb's data would have been accurately timed observations,
| as many as he could get hold of, going back about two and a
| half centuries.
| martin1975 wrote:
| If you're interested in precise time keeping, this is Time-Nuts
| is a great place to start (http://www.leapsecond.com/time-
| nuts.htm).
| mindcrime wrote:
| See also: the Metrology forum at eevblog.com. Lots of time-nuts
| (and volt-nuts, etc) hang out there.
| ryangs wrote:
| Interesting breakdown. But this format is horrible for conveying
| information. An improvement would be removing the slides,
| crafting some coherent paragraphs and then reinserting some of
| the more crucial images for support.
| m348e912 wrote:
| I have never seen this format before but it does mirror what
| going down a rabbit hole of a particular topic looks like for
| the average curious person.
|
| I liked it.
| hbn wrote:
| I was mostly confused about the images being above the line of
| text you're supposed to read before looking at the image.
|
| "Here's a picture of an NTP packet"
|
| _picture of a man sitting at a desk_
| Humdeee wrote:
| It's simply not intuitive in the way it was presented that
| the line of text was a footer for the picture. The text and
| pictures are mistakenly read as belonging to the same
| "layer", sequentially, which is not what the author intended.
| It's obvious what that intent was, but it's not structured
| correctly to be properly interpreted.
| asveikau wrote:
| I was really bothered that on the website version, the NTP
| packet diagram is largely illegible. I hope that when they
| gave this talk on slides, you could read it.
| fanf2 wrote:
| TBH you aren't supposed to read it, you either say to
| yourself, oh yes I recognise the NTP packet diagram; or, oh
| yes, that looks like a packet diagram; or, oh interesting
| maybe I should look at the NTP RFC. The slide was only up
| for a couple of seconds :-)
| zoky wrote:
| I mean, put a little gnome hat on him and I'd believe it...
| fanf2 wrote:
| When I gave the talk, I showed the slide before I talked
| about it. It's normal to show the speaker notes below the
| slides in software like Keynote or Powerpoint.
| OJFord wrote:
| That might be clearer if the header was just 'slides and
| notes from my talk', instead you actually claimed the
| opposite, that it's a 'blogified version', but it's not
| really - I tripped up on the same thing, and then got
| through several 'duplicate images', 'oh no very slightly
| different images', before it finally dawned on me that they
| were slides.
| fanf2 wrote:
| I've clarified the introductory paragraph and added lines
| between each slide. Should be a bit easier to read now.
| dclowd9901 wrote:
| I can tell the talk would have been really enjoyable but I
| agree this format is just lazy for conveying that
| information.
| FL410 wrote:
| I thought it was a very fun, stream-of-consciousness kind of
| read.
| chankstein38 wrote:
| Especially because half of the text just repeats what's on the
| slides and ultimately I didn't see an easy way to make the
| slides bigger. Like the NTP packet format slide was mostly
| unreadable.
| [deleted]
| phantom784 wrote:
| Watching the actual talk is much better:
| https://ripe86.ripe.net/archives/video/1126/
| nayuki wrote:
| The linked PDF has clear page delineations, unlike the HTML
| page:
| https://ripe86.ripe.net/presentations/134-2023-04-whence-
| tim...
| johnnyanmac wrote:
| I simply assume any "slides" format comes from porting over a
| live talk. Lazy, yes. Efficient, yes.
| NelsonMinar wrote:
| Shout out also to the NTP Pool, a volunteer group of NTP servers
| that is the common choice for a lot of devices. Particularly open
| source stuff. Microsoft, Apple, and Google all run their own time
| servers but the NTP Pool is a great resource for almost
| everything else. https://www.ntppool.org/en/
| diggan wrote:
| Reminds me of that time when the NTP pool was basically ddos'ed
| by a buggy Snapchat release to iOS devices.
| https://community.ntppool.org/t/recent-ntp-pool-traffic-incr...
| thakoppno wrote:
| This was a real talk? I would have lost my mind attending this. I
| am adding the Naval Observatory to my travel destination wish
| list.
| urbandw311er wrote:
| It's hard to tell if you "losing your mind" in this context
| means you would have enjoyed the talk or the opposite.
| thakoppno wrote:
| I would have enjoyed it tremendously.
| fanf2 wrote:
| You might also like
|
| https://dotat.at/@/2022-12-04-leap-seconds.html
|
| https://dotat.at/@/2020-11-13-leap-second-hiatus.html
| user3939382 wrote:
| A hydrogen atom being looked at by the Navy right?
| caymanjim wrote:
| Cesium, NIST.
| aa-jv wrote:
| And not just one, millions of them.
| gumby wrote:
| What a waste of taxpayers' money! They should just pick one
| and stare at it. Why should we be paying for millions of
| them???
| seanthemon wrote:
| If you don't use the budget you won't get the budget,
| sailor.
| fluoridation wrote:
| I see no downside.
| fanf2 wrote:
| The USA has two main time labs: the USNO, which provides time
| and navigation for the DoD, including the GPS; and NIST which
| provides time for civilian purposes, including WWV. NIST
| tends to do more research into new kinds of atomic clock (eg
| optical clocks, chip-scale clocks) whereas the USNO does more
| work on earth orientation.
|
| The USNO atomic clock ensemble includes caesium beam clocks,
| hydrogen masers, and rubidium fountains. NIST uses mostly
| hydrogen masers, and fewer caesium beam clocks, though their
| primary frequency standards are caesium fountains.
| vel0city wrote:
| I get the confusion for the US Navy though, as the clock is
| at the US Naval Observatory.
|
| If you ever need the time, just call (719) 567-6742
|
| "US Naval Observatory, Master Clock, at the tone, Mountain
| daylight time, nine hours, sixteen minutes, fifteen
| seconds...beep!"
| goblinux wrote:
| Just called the number holy cow it's real. I love obscure
| infrastructure stuff like that
| bityard wrote:
| When I was a kid, you could dial the operator and ask
| them for the time. I still don't know why anyone would do
| that, but I remember it was a thing you could do.
|
| Also, dialing 0 to get a human operator. I swear I'm not
| that old.
| fluoridation wrote:
| Speaking clocks are pretty common. Here we dial *133.
| hoosieree wrote:
| "At the tone?" ...what kind of ship are you running here?
| Is it at the start or the end of the tone?
| user3939382 wrote:
| Yeah according to Wikipedia anyway the USNO is operated by
| the US Navy.
| dclowd9901 wrote:
| Sort of. More like from a DNS service for time, to which the
| navy both contributes and receives information from. I found
| that part to be the most interesting.
| CableNinja wrote:
| You are sort of correct. NTP is pretty decentralized. DNS has
| a few specific servers (root servers) that all DNS eventually
| hits to find where to get a result, but, the 'tree' of DNS
| resolution is much different from that of NTP, which doesnt
| have such a tree, except as defined by any DNS entries, if
| they are used (ex pool.ntp.org has many A records for many
| ips or CNAMEs to other domains (ex 0.pool.ntp.org)).
|
| There are many contributors to the official timekeeping. Most
| facilities who do science will have their own actual atomic
| clock, which they then share out the data, in the form of an
| NTP server, however, they will not typically use data from
| the rest of the world, except for correlation events. The
| rest of the world relies on a handful of clocks which are
| either from NIST (ntp.org I think is owned by them), or from
| major providers like cloudflare (not sure they have an ntp
| server available the public can use, im almost certain that
| they would use their own atomic clock internally for security
| reasons), microsoft also has one, i think, afaik they would
| need to because they provide their own ntp pool, but they may
| just aggregate from multiple NIST servers.
|
| You can setup your own NTP server as well, and setup systems
| you own to start using it instead of whatever is configured.
| And, if one were so inclined, could even find and run your
| own atomic clock, and register it with the ntp pool. Im
| actually not sure the atomic clock is required, id hope it
| would be, but idk.
| karol wrote:
| We just create labels, which are rooted in Earths' rotation
| around the Sun at regular intervals measured by radiation and
| call it time.
| qbxk wrote:
| more importantly, where does my computer let the time go?
| [deleted]
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