| title | type | version | summary |
|---|---|---|---|
On the usage of Time in Blockchains |
monograph |
draft |
deterministic time tables and accounting |
Note
block:0 Jul-30-2015 03:26:13 PM +UTC is not the 'true' timestamp for the genesis block.
block1: GMT: Thursday, July 30, 2015 3:26:28 PM.
Thursday, July 30, 2015 8:26:28 AM GMT-07:00 DST.
see https://github.com/ethereum/go-ethereum/issues/17042#issuecomment-559414137
So, etherscan does show the genesis: etherscan.io/block/0 -- but they must have put some hack into place to make it show up as (Jul-30-2015 03:26:13 PM +UTC) -- because AFIK the actual timestamp on the genesis is all zeroes, which is 1970. Unless I'm mistaken, there's no error in geth here, possibly etherscan.
The same holds when querying a node running Parity: timestamp for block 0 is 0. On the other hand, etherscan.io shows Jul-30-2015 03:26:13 PM +UTC as timestamp for the genesis block. It would be nice to have a consistent view, or at least an explanation like "0 is correct, etherscan is just extrapolating".
Resources for utilizing time on-chain
Block timestamps have historically been used for a variety of applications, such as entropy for random numbers (see the Entropy Illusion section for further details), locking funds for periods of time and various state-changing conditional statements that are time-dependent. Miner's have the ability to adjust timestamps slightly which can prove to be quite dangerous if block timestamps are used incorrectly in smart contracts.
Some useful references for this are: The Solidity Docs, this Stack Exchange Question.
block.timestamp or its alias now (depreciated) can be manipulated by miners if they have some incentive to do so. Let's construct a simple game, which would be vulnerable to miner exploitation,
// roulette.sol:
contract Roulette {
uint public pastBlockTime; // Forces one bet per block
constructor() public payable {} // initially fund contract
// fallback function used to make a bet
function () public payable {
require(msg.value == 10 ether); // must send 10 ether to play
require(now != pastBlockTime); // only 1 transaction per block
pastBlockTime = now;
if(now % 15 == 0) { // winner
msg.sender.transfer(this.balance);
}
}
}This contract behaves like a simple lottery. One transaction per block can bet 10 ether for a chance to win the balance of the contract. The assumption here is that, block.timestamp is uniformly distributed about the last two digits. If that were the case, there would be a 1/15 chance of winning this lottery.
However, as we know, miners can adjust the timestamp, should they need to. In this particular case, if enough ether pooled in the contract, a miner who solves a block is incentivised to choose a timestamp such that block.timestamp or now modulo 15 is 0. In doing so they may win the ether locked in this contract along with the block reward. As there is only one person allowed to bet per block, this is also vulnerable to front-running attacks.
Note block timestamps are monotonically increasing and so miners cannot choose arbitrary block timestamps (true for Ethereum1)
In practice, block timestamps are monotonically increasing and so miners cannot choose arbitrary block timestamps (they must be larger than their predecessors). They are also limited to setting blocktimes not too far in the future as these blocks will likely be rejected by the network (nodes will not validate blocks whose timestamps are in the future).
Block timestamps should not be used for entropy or generating random numbers - i.e. they should not be the deciding factor (either directly or through some derivation) for winning a game or changing an important state (if assumed to be random).
Time-sensitive logic is sometimes required; i.e. unlocking contracts (timelocking), completing an ICO after a few weeks or enforcing expiry dates. It is sometimes recommend to use block.number (see the Solidity docs) and an average block time to estimate times; .i.e. 1 week with a 10 second block time, equates to approximately, 60480 blocks. Thus, specifying a block number at which to change a contract state can be more secure as miners are unable to manipulate the block number as easily. The BAT ICO contract employed this strategy.
This can be unnecessary if contracts aren't particularly concerned with miner manipulations of the block timestamp, but it is something to be aware of when developing contracts.
IEEE Std 1003.1-1988 (POSIX.1) legislates that a time_t value of
536457599 shall correspond to "Wed Dec 31 23:59:59 GMT 1986." This
effectively implies that POSIX time_t's cannot include leap seconds and,
therefore, that the system time must be adjusted as each leap occurs.
The C and POSIX standards define for the strftime() function and the date utility a notation for defining date and time representations. Here are some examples, of how they can be used to produce ISO 8601 output:
format string output
%Y-%m-%d 1999-12-31
%Y-%j 1999-365
%G-W%V-%u 1999-W52-5
%H:%M:%S 23:59:59date --rfc-3339=seconds | sed 's/ /T/'
> 2021-03-29T19:12:08-07:00date -u +"%Y-%m-%d %H-%M-%SZ"
date -u +"%Y-%m-%dT%H:%MZ"Z and +00:00 are the same (mostly). For purposes of translating time, they both mean UTC. However England is +00:00 in winter and +01:00 in summer (BST). Z is UTC, while +00:00 is GMT.
GNU date date -I is the same as date +%F, and -Iseconds and
Iminutes also include time with UTC offset.
date +%F # -I or +%Y-%m-%d
date +%FT%T%z # -Iseconds or +%Y-%m-%dT%H:%M:%S%z
date +%FT%H:%M # -Iminutes or +%Y-%m-%dT%H:%M%z
date -u +%FT%TZ20130503T15 (%Y%m%dT%M)
2013-05 (%Y%m)
2013-W18 (%Y-W%V)
2013-W18-5 (%Y-W%V-%u)
2013W185 (%YW%V%u)
2013-123 (%Y-%j, ordinal date)
2013 (%Y)
1559 (%H%M)
15 (%H)
15:59:24+03 (UTC offset doesn't have to include minutes)$ date -u -Iseconds
$ date -u '+%Y-%m-%dT%k:%M:%S%z'| From | To | On | At | Action | **** |
|---|---|---|---|---|---|
| 1918 | 1919 | last Sunday | in March | 02:00 local | go to daylight saving time |
| in October | return to standard time | ||||
| 1942 only | February 9th | go to “war time” | |||
| 1945 only | August 14th | 23:00 UT | rename “war time” to “peace | ||
| time;” clocks don’t change | |||||
| September 30th | 02:00 local | return to standard time | |||
| 1967 | 2006 | last Sunday | in October | ||
| 1973 | in April | go to daylight saving time | |||
| 1974 only | January 6th | ||||
| 1975 only | February 23rd | ||||
| 1976 | 1986 | last Sunday | in April | ||
| 1987 | 2006 | first Sunday | |||
| 2007 | present | second Sunday in March | |||
| first Sunday in November | return to standard time |
| cal_system | AverageYear(Days) | ErrorPerYear(Days) | ErrorRatio | CylcePeriod | 1-DayShift | 100-yearError(Days) |
|---|---|---|---|---|---|---|
| 365 | 365 | 0.2422 | 6.63 xx10-4 | 1,508 | 4.129 | 24.22 |
| Julian | 365.25 | -0.0078 | 2.14 xx10-5 | 46,826 | 128.2 | 0.78 |
| Gregorian | 365.2425 | -0.0003 | 8.2 xx10-7 | 1,200,000 | 3,333.30 | 0.03 |
| 4000 | 365.24225 | -0.00005 | 1.4 xx10-7 | 7,300,000 | 20,000 | 0.005 |
| 2//900 | 365.2422 | -0.000022 | 6.1 xx10-8 | 16,000,000 | 45,000 | 0.002 |
| Jalaali | 365.242424 | -0.000224 | 6.1 xx10-7 | 1,600,000 | 4,460 | 0.02 |
| 31//128 | 365.24218750 .0000125 | 0 .0000125 | 3.4 xx10-8 | 29,000,000 | 80,000 | 0.001 |
| Layman time | Seconds |
|---|---|
| 1 minute | 60 |
| 5 minutes | 300 |
| 10 minutes | 600 |
| 30 minutes | 1800 |
| 1 hour | 3600 |
| 2 hours | 7200 |
| 4 hours | 14400 |
| 6 hours | 21600 |
| 8 hours | 28800 |
| 12 hours | 43200 |
| 1 day | 86400 |
| 2 days | 172800 |
| 3 days | 259200 |
| 4 days | 345600 |
| 5 days | 432000 |
| 6 days | 518400 |
| 1 week | 604800 |
| 2 weeks | 1209600 |
| 4 weeks | 2419200 |
| 1 month (30 days) | 2592000 |
| 1 month (avg. 30.44 days) | 2629743 |
| 1 month (31 days) | 2678400 |
| 1 year (365 days) | 31536000 |
| 1 year (avg. 365.24 days) | 31556926 |
| leap year (366 days) | 31622400 |
| Regular date | Unix timestampGMT/UTC |
|---|---|
| 1930, January 1 | -1262304000 |
| 1931, January 1 | -1230768000 |
| 1932, January 1 | -1199232000 |
| 1933, January 1 | -1167609600 |
| 1934, January 1 | -1136073600 |
| 1935, January 1 | -1104537600 |
| 1936, January 1 | -1073001600 |
| 1937, January 1 | -1041379200 |
| 1938, January 1 | -1009843200 |
| 1939, January 1 | -978307200 |
| 1940, January 1 | -946771200 |
| 1941, January 1 | -915148800 |
| 1942, January 1 | -883612800 |
| 1943, January 1 | -852076800 |
| 1944, January 1 | -820540800 |
| 1945, January 1 | -788918400 |
| 1946, January 1 | -757382400 |
| 1947, January 1 | -725846400 |
| 1948, January 1 | -694310400 |
| 1949, January 1 | -662688000 |
| 1950, January 1 | -631152000 |
| 1951, January 1 | -599616000 |
| 1952, January 1 | -568080000 |
| 1953, January 1 | -536457600 |
| 1954, January 1 | -504921600 |
| 1955, January 1 | -473385600 |
| 1956, January 1 | -441849600 |
| 1957, January 1 | -410227200 |
| 1958, January 1 | -378691200 |
| 1959, January 1 | -347155200 |
| 1960, January 1 | -315619200 |
| 1961, January 1 | -283996800 |
| 1962, January 1 | -252460800 |
| 1963, January 1 | -220924800 |
| 1964, January 1 | -189388800 |
| 1965, January 1 | -157766400 |
| 1966, January 1 | -126230400 |
| 1967, January 1 | -94694400 |
| 1968, January 1 | -63158400 |
| 1969, January 1 | -31536000 |
| 1970, January 1 | 0 |
| 1971, January 1 | 31536000 |
| 1972, January 1 | 63072000 |
| 1973, January 1 | 94694400 |
| 1974, January 1 | 126230400 |
| 1975, January 1 | 157766400 |
| 1976, January 1 | 189302400 |
| 1977, January 1 | 220924800 |
| 1978, January 1 | 252460800 |
| 1979, January 1 | 283996800 |
| 1980, January 1 | 315532800 |
| 1981, January 1 | 347155200 |
| 1982, January 1 | 378691200 |
| 1983, January 1 | 410227200 |
| 1984, January 1 | 441763200 |
| 1985, January 1 | 473385600 |
| 1986, January 1 | 504921600 |
| 1987, January 1 | 536457600 |
| 1988, January 1 | 567993600 |
| 1989, January 1 | 599616000 |
| 1990, January 1 | 631152000 |
| 1991, January 1 | 662688000 |
| 1992, January 1 | 694224000 |
| 1993, January 1 | 725846400 |
| 1994, January 1 | 757382400 |
| 1995, January 1 | 788918400 |
| 1996, January 1 | 820454400 |
| 1997, January 1 | 852076800 |
| 1998, January 1 | 883612800 |
| 1999, January 1 | 915148800 |
| 2000, January 1 | 946684800 |
| 2001, January 1 | 978307200 |
| 2002, January 1 | 1009843200 |
| 2003, January 1 | 1041379200 |
| 2004, January 1 | 1072915200 |
| 2005, January 1 | 1104537600 |
| 2006, January 1 | 1136073600 |
| 2007, January 1 | 1167609600 |
| 2008, January 1 | 1199145600 |
| 2009, January 1 | 1230768000 |
| 2010, January 1 | 1262304000 |
| 2011, January 1 | 1293840000 |
| 2012, January 1 | 1325376000 |
| 2013, January 1 | 1356998400 |
| 2014, January 1 | 1388534400 |
| 2015, January 1 | 1420070400 |
| 2016, January 1 | 1451606400 |
| 2017, January 1 | 1483228800 |
| 2018, January 1 | 1514764800 |
| 2019, January 1 | 1546300800 |
| 2020, January 1 | 1577836800 |
| 2021, January 1 | 1609459200 |
| 2022, January 1 | 1640995200 |
| 2023, January 1 | 1672531200 |
| 2024, January 1 | 1704067200 |
| 2025, January 1 | 1735689600 |
| 2026, January 1 | 1767225600 |
| 2027, January 1 | 1798761600 |
| 2028, January 1 | 1830297600 |
| 2029, January 1 | 1861920000 |
| 2030, January 1 | 1893456000 |
| 2031, January 1 | 1924992000 |
| 2032, January 1 | 1956528000 |
| 2033, January 1 | 1988150400 |
| 2034, January 1 | 2019686400 |
| 2035, January 1 | 2051222400 |
| 2036, January 1 | 2082758400 |
| 2037, January 1 | 2114380800 |
| 2038, January 1 | 2145916800 |
| imestamp Format | Example |
|---|---|
| yyyy-MM-dd'T'HH:mm:ss*SSSZZZZ | 2018-08-20'T'13:20:10*633+0000 |
| yyyy MMM dd HH:mm:ss.SSS zzz | 2017 Mar 03 05:12:41.211 PDT |
| MMM dd HH:mm:ss ZZZZ yyyy | Jan 21 18:20:11 +0000 2017 |
| dd/MMM/yyyy:HH:mm:ss ZZZZ | 19/Apr/2017:06:36:15 -0700 |
| MMM dd, yyyy hh:mm:ss a | Dec 2, 2017 2:39:58 AM |
| MMM dd yyyy HH:mm:ss | Jun 09 2018 15:28:14 |
| MMM dd HH:mm:ss yyyy | Apr 20 00:00:35 2010 |
| MMM dd HH:mm:ss ZZZZ | Sep 28 19:00:00 +0000 |
| MMM dd HH:mm:ss | Mar 16 8:12:04 |
| yyyy-MM-dd'T'HH:mm:ssZZZZ | 2017-10-14T22:11:20+0000 |
| yyyy-MM-dd'T'HH:mm:ss.SSS'Z' | 2017-07-01T14:59:55.711'+0000'2017-07-01T14:59:55.711Z |
| yyyy-MM-dd HH:mm:ss ZZZZ | 2017-08-19 12:17:55 -0400 |
| yyyy-MM-dd HH:mm:ssZZZZ | 2017-08-19 12:17:55-0400 |
| yyyy-MM-dd HH:mm:ss,SSS | 2017-06-26 02:31:29,573 |
| yyyy/MM/dd*HH:mm:ss | 2017/04/12*19:37:50 |
| yyyy MMM dd HH:mm:ss.SSS*zzz | 2018 Apr 13 22:08:13.211*PDT |
| yyyy MMM dd HH:mm:ss.SSS | 2017 Mar 10 1:44:20 |
| yyyy-MM-dd HH:mm:ss,SSSZZZZ | 2017-03-10 14:30:12,655+0000 |
| yyyy-MM-dd HH:mm:ss.SSS | 2018-02-27 15:35:20 |
| yyyy-MM-dd HH:mm:ss.SSSZZZZ | 2017-03-12 13:11:34.222-0700 |
| yyyy-MM-dd'T'HH:mm:ss.SSS | 2017-07-22'T'16:28:55.444 |
| yyyy-MM-dd'T'HH:mm:ss | 2017-09-08'T'03:13:10 |
| yyyy-MM-dd'T'HH:mm:ss'Z' | 2017-03-12'T'17:56:22'-0700' |
| yyyy-MM-dd'T'HH:mm:ss.SSS | 2017-11-22'T'10:10:15.455 |
| yyyy-MM-dd'T'HH:mm:ss | 2017-02-11'T'18:31:44 |
| yyyy-MM-dd*HH:mm:ss:SSS | 2017-10-30*02:47:33:899 |
| yyyy-MM-dd*HH:mm:ss | 2017-07-04*13:23:55 |
| yy-MM-dd HH:mm:ss,SSS ZZZZ | 11-02-11 16:47:35,985 +0000 |
| yy-MM-dd HH:mm:ss,SSS | 10-06-26 02:31:29,573 |
| yy-MM-dd HH:mm:ss | 10-04-19 12:00:17 |
| yy/MM/dd HH:mm:ss | 06/01/22 4:11:05 |
| yyMMdd HH:mm:ss | 150423 11:42:35 |
| yyyyMMdd HH:mm:ss.SSS | 20150423 11:42:35.173 |
| MM/dd/yy*HH:mm:ss | 08/10/11*13:33:56 |
| MM/dd/yyyy*HH:mm:ss | 11/22/2017*05:13:11 |
| MM/dd/yyyyHH:mm:ssSSS | 05/09/201708:22:14612 |
| MM/dd/yy HH:mm:ss ZZZZ | 04/23/17 04:34:22 +0000 |
| MM/dd/yyyy HH:mm:ss ZZZZ | 10/03/2017 07:29:46 -0700 |
| HH:mm:ss | 11:42:35 |
| HH:mm:ss.SSS | 11:42:35 |
| HH:mm:ss,SSS | 11:42:35,173 |
| dd/MMM HH:mm:ss,SSS | 23/Apr 11:42:35,173 |
| dd/MMM/yyyy:HH:mm:ss | 23/Apr/2017:11:42:35 |
| dd/MMM/yyyy HH:mm:ss | 23/Apr/2017 11:42:35 |
| dd-MMM-yyyy HH:mm:ss | 23-Apr-2017 11:42:35 |
| dd-MMM-yyyy HH:mm:ss.SSS | 23-Apr-2017 11:42:36 |
| dd MMM yyyy HH:mm:ss | 23 Apr 2017 11:42:35 |
| dd MMM yyyy HH:mm:ss*SSS | 23 Apr 2017 10:32:35*311 |
| MMdd_HH:mm:ss | 0423_11:42:35 |
| MMdd_HH:mm:ss.SSS | 0423_11:42:35.883 |
| MM/dd/yyyy hh:mm:ss a:SSS | 8/5/2011 3:31:18 AM:234 |
| MM/dd/yyyy hh:mm:ss a | 9/28/2011 2:23:15 PM |
| Token | Date or Time Component | Example |
|---|---|---|
| yyyy | 4-digit year | 2012; 2016 |
| yy | 2-digit year | 12; 16 |
| MMM | 3-character month | Jan; Mar; Dec |
| MM | 1- or 2-digit month (in a year) | 1; 01; 9; 09; 12 |
| dd | 1- or 2-digit day (in a month) | 1; 01; 16; 30 |
| a | AM/PM (case insensitive) | AM; PM; am; pm |
| HH | 1- or 2-digit hour (in a day, 0-23) | 2; 02; 14; 23 |
| hh | 1- or 2-digit hour (in a day, 1-12 with AM/PM) | 2; 02; 11; 12 |
| mm | 1- or 2-digit minute (in an hour) | 8; 08; 55 |
| ss | 1- or 2-digit second (in a minute) | 5; 05; 35 |
| SSS | 1-3 digit subsecond or millisecond (in decimal) | 4; 58; 944 |
| zzz | 3- letter time zone | UTC; PST; EDT |
| ZZZZ | RFC 822 time zone | -0900; +0500 |
| Z' | Literal Z character | Z |
| T' | Literal T character | T |
| epoch | 10, 13, 16, 19 digit timestamp with optional . (dot) after 10 digits. | 1496756807 |
| Country | End Julian Calendar | Begin Gregorian Calendar |
|---|---|---|
| Albania | Dec 1912 | Dec 1912 |
| Austria Tyrol Carinthia, Styria |
Oct 5, 1583 Dec 14, 1583 |
Oct 16,1583 Dec 25, 1583 |
| Belgium Spanish Provinces Liege |
Dec 21, 1582 Feb 10,1583 |
Jan 1, 1583 Feb 21,1583 |
| Bulgaria | Nov 1, 1915 | Nov 14, 1915 |
| China | Dec 18, 1911 | Jan 1, 1912 |
| Canada British Colonies Nova Scotia |
Sep 2, 1752 Sep 2, 1752 |
Sep 14, 1752 Sep 14, 1752 |
| Czech Republic - Bohemia / Moravia | Jan 6, 1584 | Jan 17, 1584 |
| Denmark Faero Islands |
Feb 18, 1700 Nov 16, 1700 |
March 1,1700 Nov 28, 1700 |
| Egypt | 1875 | 1875 |
| Estonia | Feb 1, 1918 | Feb 15, 1918 |
| Finland (part of Sweden) | Feb 17, 1753 | March 1, 1753 |
| France & Colonies Alsace Strasbourg |
Dec 9, 1582 1648 Feb 5, 1682 |
Dec 20, 1582 1648 Feb 16,1682 |
| Germany, Catholic Regions Augsburg Baden Bavaria Cologne Julich Mainz Munster, Strasbourg Trier Wurzburg |
Feb 13, 1583 Nov 16, 1583 Oct 5, 1583 Nov 3, 1583 Nov 2, 1583 Nov 11, 1583 Nov 16, 1583 Oct 4, 1583 Nov 4, 1583 |
Feb 24, 1583 Nov 27, 1583 Nov 16, 1583 Nov 14, 1583 Nov 13, 1583 Nov 22, 1583 Nov 27, 1583 Oct, 15, 1583 Nov 15, 1583 |
| Germany, Protestant Regions Hildesheim Kurland Minden Neuburg Osnabruck Paderborn Prussia Westphalia All Others |
Mar 15, 1631 1617 Feb 1, 1668 Dec 13, 1615 1624 June 16, 1585 Aug 22, 1610 July 1, 1584 Feb 18, 1700 |
March 26, 1631 1617 Feb 12, 1668 Dec 24, 1615 1624 July 27, 1585 Sept 2, 1610 July 12, 1584 March 1, 1700 |
| Great Britain & colonies | Sept 2, 1752 | Sept 14, 1752 |
| Greece | Sept 14, 1916 | Sept 28, 1916 |
| Holy Roman Empire | Jan 6, 1584 | Jan 17, 1584 |
| Hungary Transylvania |
Oct 21, 1587 Dec 14, 1590 |
Nov 1, 1587 Dec 25, 1590 |
| Iceland | Nov 16, 1700 | Nov 28, 1700 |
| Ireland | Sept 2, 1752 | Sept 14, 1752 |
| Italy | Oct 4,1582 | Oct 15, 1582 |
| Japan | 1873 | 1873 |
| Latvia | Feb 1, 1918 | Feb 15, 1918 |
| Lithuania | Feb 1, 1918 | Feb 15, 1918 |
| Moravia (Czech Republic) | Jan 6, 1584 | Jan 17, 1584 |
| The Netherlands Holland, North Brabant Gelderland, Zutphen Utrecht, Overijssel Friesland, Groningen Drente |
Dec 21, 1582 June 30, 1700 Nov 30, 1700 Dec 31, 1700 April 30, 1701 |
Jan 1, 1583 July 7, 1700 Dec 12, 1700 Jan 12, 1701 May 12, 1701 |
| Norway | Feb 18, 1700 | March 1, 1700 |
| Poland Silesia |
Oct 4, 1582 Jan 12, 1584 |
Oct 15, 1582 Jan 23, 1584 |
| Portugal | Oct 4, 1582 | Oct 15, 1582 |
| Romania Transylvania |
March 31, 1919 Dec 14, 1590 |
April 14, 1919 Dec 25, 1590 |
| Russia | Jan 31,1918 | Feb 14, 1918 |
| Spain American Colonies |
Oct 4, 1582 1584 |
Oct 15, 1582 1584 |
| Sweden | Feb 17, 1753 | March 1, 1753 |
| Switzerland Catholic Cantons - Lucern, Uri, Schwyz, Zug, Freiburg, Solothurn Wallis Protestant - Zurich, Bern, Basel, Schaffhouse, Geneva, Thurgovia Appenzell, Glarus, St. Gallen |
Jan 11, 1584 Jan 11, 1584 Feb 28, 1655 Dec 31, 1700 Dec 31, 1700 1724 |
Jan 22, 1584 Jan 22, 1584 March 11, 1655 Jan 12, 1701 Jan 12, 1701 1724 |
| Turkey | 1927 | 1927 |
| United States British Colonies Spanish Colonies Alaska |
Sept 2, 1752 1584 Oct 5, 1867 |
Sept 14, 1752 1584 Oct 18, 1867 |
| Yugoslavia | March 4, 1919 | March 18, 1919 |
https://pumas.nasa.gov/files/04_21_97_1.pdf
Timestamps, Time-Zones, Time-Ranges, and Date-Formats#Timestamp_conventions