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Information about Snow

This article is about the stream cipher. For the MI5 agent, see Arthur Owens.
SNOW 1.0 and 2.0 are two word-based synchronous stream ciphers developed by Thomas Johansson and Patrik Ekdahl at Lund University.

SNOW 1.0, originally simply SNOW, was submitted to the NESSIE project. The cipher has no known intellectual property or other restrictions. The cipher works on 32-bit words and supports both 128- and 256-bit keys. The cipher consists of a combination of a LFSR and a Finite State Machine (FSM) where the LFSR also feeds the next state function of the FSM. The cipher has a short initialization phase and very good performance on both 32-bit processors and in hardware.

During the NESSIE evaluation weaknesses was discovered and SNOW was therefore not included in the NESSIE suite of algorithms. The authors has developed a new version, version 2.0 of the cipher, that solves the weaknesses and improves the performance.

SNOW has been used in the ESTREAM project as a reference cipher for the performance evaluation.

External links

Stream ciphers
 •  • [ e]
Algorithms: A5/1 | A5/2 | E0 | FISH | Grain | HC-256 | ISAAC | LILI-128 | MUGI | Panama | Phelix | Pike | Py | Rabbit | RC4 | Salsa20 | Scream | SEAL | SOBER | SOBER-128 | SOSEMANUK | Trivium | VEST | WAKE
Theory: Shift register | LFSR | NLFSR | Shrinking generator | T-function | IV   Standardization: eSTREAM
Cryptography
 •  • [ e]
History of cryptography | Cryptanalysis | | Topics in cryptography
Symmetric-key algorithm | Block cipher | Stream cipher | Public-key cryptography | Cryptographic hash function | Message authentication code | Random numbers


For other uses, see snow (disambiguation).
SNoW (pronounced: "Snow", born June 11, 1985 in Tokyo, Japan) is a J-Pop singer. She currently attends Santa Monica College in California. She has grown up in a bilingual environment. Her favorite artists include Ani DiFranco, Iggy Pop, Talking Heads, and Jack Johnson.

Her debut single Yes was released under an indie record label in November 2004. In 2005, she switched labels to Sony Music Entertainment Japan and released Hanabi made Ato Sukoshi (花火まであとすこし - unofficial translation: "A Little Longer Until the Fireworks") in July. Her third single, Sakasama no Chō (逆さまの蝶 - unofficial translation: "The Inverted Butterfly"), was released on January 25, 2006. Sakasama no Chō was the opening theme of the 2005/2006 anime Jigoku Shoujo (地獄少女), and will be inserted into the movie Humoresque ~Sakasama no Chō~, to be released in February 2006. The opening theme for Jigoku Shōjo's second season, NightmaRe, was also performed by SNoW, and was released as a single on December 6, 2006.

Discography

Singles

  • Yes - November 25, 2004
  • Hanabi Made Ato Sukoshi - July 6, 2005
  • Sakasama no Chō - January 25, 2006
  • on&on - July 5, 2006
  • NightmaRe - December 6, 2006

Albums

初雪(Hatsuyuki) - January 23, 2007

External links

Official websites in Japanese:


Part of the Nature series on
Weather
 
Seasons
Temperate
• Spring • Summer •
• Autumn • Winter •
Tropical
• Dry season •
• Wet season
Storms
• Thunderstorm • Tornado •
• Tropical Cyclone (Hurricane) •
• Winter storm • Blizzard
Precipitation
• Fog • Drizzle • Rain •
• Freezing rain • Sleet •
• Hail • Snow
Topics
• Meteorology •
• Weather forecasting •
• Climate • Air pollution •
Project   •  • [ e] 


Snow is a type of precipitation in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. Since snow is composed of small ice particles, it is a granular material. It has an open and therefore soft structure, unless packed by external pressure.

Snowflakes

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Animation of snowcover changing with the seasons
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Trees covered with snow
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The "Japanese Tsuzumi", an unusual variation of snow crystal, is named after the hourglass-shaped tsuzumi drum.
A snowflake is an aggregate of ice crystal that forms while falling in and below a cloud. They are typically hexagonally symmetrical.[1]

Geometry

Large, well formed snowflakes are relatively flat and have six approximately identical arms, so that the snowflake nearly has the same 6-fold dihedral symmetry as a hexagon or hexagram. This symmetry arises from the hexagonal crystal structure of ordinary ice. However, the exact shape of the snowflake is determined by the temperature and humidity at which it forms.[1]. Rarely, at a temperature of around -2 °C (28 °F), snowflakes can form in threefold symmetry - triangular snowflakes. [2] Snowflakes are not perfectly symmetric however. The most common snowflakes are visibly irregular, although near-perfect snowflakes may be more common in pictures because they are more visually appealing.

Snowflakes can come in many different forms, including columns, needles, and plates (with and without "dendrites" - the "arms" of some snowflakes). These different forms arise out of different temperatures and water saturation - among other conditions. Six petaled ice flowers grow in air between 0 °C (32 °F) and -3 °C (27 °F). The vapor droplets solidify around a dust particle. Between temperatures of -1 °C (30 °F) and -3 °C (27 °F), the snowflake will be in the form of a dendrite or a plate or the six petaled ice flower. As temperatures get colder, between -5 °C (23 °F) and -10 °C (14 °F), the crystals will form in needles or hollow columns or prisms. When the temperature becomes even colder (from -10 °C to -22 °C) the ice flowers are formed again, and at temperatures below -22 °C, the vapors will turn into prisms again. If a crystal has started forming at around -5 °C, and is then exposed to warmer or colder temperatures, a capped column may be formed which consists of a column-like design capped with a dendrite or plate-like design on each end of the column.[1] At even colder temperatures, the snowflake design returns to the more common dendrite and plate. At temperatures approaching -20 °C, sectored plates are formed which appears as a dendrite, with each dendrite appearing flattened, like the design of a snowflake plate.[1]

There are, broadly, two possible explanations for the symmetry of snowflakes. First, there could be communication or information transfer between the arms, such that growth in each arm affects the growth in each other arm. Surface tension or phonons are among the ways that such communication could occur. The other explanation, which appears to be the prevalent view, is that the arms of a snowflake grow independently in an environment that is believed to be rapidly varying in temperature, humidity and other atmospheric conditions. This environment is believed to be relatively spatially homogeneous on the scale of a single flake, leading to the arms growing to a high level of visual similarity by responding in identical ways to identical conditions, much in the same way that unrelated trees respond to environmental changes by growing near-identical sets of tree rings. The difference in the environment in scales larger than a snowflake leads to the observed lack of correlation between the shapes of different snowflakes. The sixfold symmetry happens because of the basic hexagonal crystalline structure from which the snowflake grows. The exact reason for the threefold symmetry of triangular snowflakes is still a mystery although trigonal symmetry is a subsymmetry of hexagonal.

There is a widely held belief that no two snowflakes are alike. Strictly speaking, it is extremely unlikely for any two macroscopic objects in the universe to contain an identical molecular structure; but there are, nonetheless, no known scientific laws that prevent it. In a more pragmatic sense, it's more likely—albeit not much more—that two snowflakes are visually identical if their environments were similar enough, either because they grew very near one another, or simply by chance. The American Meteorological Society has reported that matching snow crystals were discovered in Wisconsin in 1988 by Nancy Knight of the National Center for Atmospheric Research. The crystals were not flakes in the usual sense but rather hollow hexagonal prisms.
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Snowflake Gallery.

Snow on the ground

Snow fall remains on the ground until it melts. In colder climates this results in snow lying on the ground all winter; when the snow does not all melt in the summer it becomes glaciers.

This is often called snowpack, especially when it does persist a long time. The deepest snowpacks occur in mountainous regions. It is influenced by temperature and wind events which determine melting, accumulation and wind erosion.

The water equivalent of the snow is thickness of the layer of water having the same content. For example, if the snow covering a given area has a water equivalent of 50 cm (20 in), then it will melt into a pool of water 50 cm (20 in) deep covering the same area. This is a much more useful measurement to hydrologists than snow depth, as the density of even freshly fallen snow widely varies. New snow commonly has a density of between 5% and 15% of water. Snow that falls in maritime climates is usually denser than snow that falls in mid-continent locations because of the higher average temperatures over oceans than over land masses. Cloud temperatures and physical processes in the cloud affect the shape of individual snow crystals. Highly branched or dendritic crystals tend to have more space between the arms of ice that form the snow flake and this snow will therefore have a lower density, often referred to as "dry" snow. Conditions that create columnar or platelike crystals will have much less air space within the crystal and will therefore be more dense and feel "wetter".

Once the snow is on the ground, it will settle under its own weight (largely due to differential evaporation) until its density is approximately 30% of water. Increases in density above this initial compression occur primarily melting and refreezing, caused by temperatures above freezing or by direct solar radiation. By late spring, snow densities typically reach a maximum of 50% of water.[3]

Spring snow melt is a major source of water supply to areas in temperate zones near mountains that catch and hold winter snow, especially those with a prolonged dry summer. In such places, water equivalent is of great interest to water managers wishing to predict spring runoff and the water supply of cities downstream. Measurements are made manually at marked locations known as snow courses, and remotely using special scales called snow pillows.

Many rivers originating in mountainous or high-latitude regions have a significant portion of their flow from snowmelt. This often makes the river's flow highly seasonal resulting in periodic flooding. In contrast, if much of the melt is from glaciated or nearly glaciated areas, the melt continues through the warm season, mitigating that effect.

Energy balance

The energy balance of the snowpack is dictated by several heat exchange processes. The snowpack absorbs solar shortwave radiation that is partially blocked by cloud cover and reflected by snow surface. A longwave heat exchange takes place between the snowpack and its surrounding environment that includes overlaying air mass, tree cover and clouds. Convective (sensible) heat exchange between the snowpack and the overlaying air mass is governed by the temperature gradient and wind speed. Moisture exchange between the snowpack and the overlaying air mass is accompanied with latent heat transfer that is influenced by vapor pressure gradient and air wind. Rain on snow could induce significant heat input to the snowpack. A generally insignificant conductive heat exchange takes place between the snowpack and the underlying ground. [4]

Impact on human society

Snow serves as a thermal insulator conserving the heat of the Earth and protecting crops from subfreezing weather. But substantial snowfall sometimes disrupts infrastructure and services, even those of a region that is accustomed to such weather. Automotive traffic may be greatly inhibited or may be stifled entirely. Basic infrastructures such as electricity, telephone lines, and gas supply can also be shut down. This can lead to a "snow day," a day on which school sessions or other services are canceled owing to an unusually heavy snowfall.

In areas that normally have very little or no snow, a snow day may occur with light accumulation or even the threat of snowfall, as those areas are ill prepared to handle any amount of snow. A mudslide, flash flood, or avalanche can occur when excessive snow has accumulated on a mountain and there is a sudden change of temperature.

Records

The highest seasonal total snowfall ever measured was at Mount Baker Ski Area, outside of Bellingham, Washington in the United States during the 1998–1999 season. Mount Baker received 1,140 inches (29 m) of snow,[5] thus surpassing the previous record holder, Mount Rainier, Washington, which during the 1971–1972 season received 1,122 in. (28.5 m) of snow.[6] Guinness World Records list the world’s largest snowflakes as those of January 1887 at Fort Keogh, Montana;. allegedly one measured 15 inches (38 cm) wide.

Recreation

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Building a snowman.
Some forms of recreation depend on snow

Types of snow

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Hoar frost that grows on the snow surface due to water vapor moving up through the snow on cold, clear nights

Snow falling

Blizzard
A long-lasting snow storm with intense snowfall and usually high winds. Particularly severe storms can create whiteout conditions where visibility is reduced to less than 1 m.
Flurry
A period of light snow with usually little accumulation with occasional moderate snowfall.
Freezing rain
Rain that freezes on impact with a sufficiently cold surface. This can cover trees in a uniform layer of very clear, shiny ice – a beautiful phenomenon, though excessive accumulation can break tree limbs and utility lines, causing utility failures and possible property damage.
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Snowbird ski resort, one of the snowiest places in the U.S.
Graupel
Precipitation formed when freezing fog condenses on a snowflake, forming a ball of rime ice. Also known as snow pellets.
Ground blizzard
Occurs when a strong wind drives already fallen snow to create drifts and whiteouts.
Hail
Many-layered ice balls, ranging from "pea" sized (0.25 in, 6 mm) to "golf ball" sized (1.75 in, 43 mm), to, in rare cases, "softball" sized or greater (­>4.25 in, 108 mm).
Hailstorm
A storm of hail. If the hail is sufficiently large, it can cause damage to cars or even people.
Lake effect snow
Produced when cold winds move across long expanses of warmer lake water, picking up water vapor which freezes and is deposited on the lake's shores.
Pukak
A layer at the bottom of old snowpack, consisting of coarse, sugar-like ice crystals and air. Subnivean animals live in the pukak layer because its temperature is generally stable at a few degrees below freezing and it can be tunneled through with relative ease.
Sleet
In Britain, rain mixed with snow; in America, ice pellets formed when snowflakes pass through a layer of warm air, partially thaw, then refreeze on further descent.
Snow pellets
See graupel.
Snow squall
A brief, very intense snowstorm.
Snow storm
A long storm of relatively heavy snow.
Soft hail
of snow or ice pellets formed when supercooled water accretes on ice crystals or snowflakes.
Thundersnow
A thunderstorm which produces snow as the primary form of precipitation.

Snow on the ground

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Snow covering a leaf.
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Snow blowing from a roof in Ottawa
Artificial snow
Snow can be also manufactured using snow cannons, which actually create tiny granules more like soft hail (this is sometimes called "grits" by those in the southern U.S. for its likeness to the texture of the food). In recent years, snow cannons have been produced that create more natural-looking snow, but these machines are prohibitively expensive.
Blowing snow
Snow on ground that is being moved around by wind. See ground blizzard.
Corn
Coarse, granular wet snow. Most commonly used by skiers describing good spring snow. Corn is the result of diurnal cycle of melting and refreezing.
Crust
A double layer of snow in which the lower layer may be powdery dry but where the surface is frozen together into a stiff, icy surface, which often can support human weight.
Ice
Densely packed material formed from snow that doesn't contain air bubbles. Depending on the snow accumulation rate, the air temperature, and the weight of the snow in the upper layers, it can take snow a few hours or a few decades to form into ice.
Firn
Snow which has been lying for at least a year but which has not yet consolidated into glacier ice. It is granular.
Packed Powder
The most common snow cover on ski slopes, consisting of powder snow that has lain on the ground long enough to become compressed, but is still loose.
Packing snow
Snow that is at or near the melting point, so that it can easily be packed into snowballs and hurled at other people or objects. This is perfect for snow fights and other winter fun, such as making a snowman, or a snow fort.
Penitentes
Tall blades of snow found at high altitudes.
Powder
Freshly fallen, uncompacted snow. The density and moisture content of powder snow can vary widely; snowfall in coastal regions and areas with higher humidity is usually heavier than a similar depth of snowfall in an arid or continental region. Light, dry (low moisture content) powder snow is prized by skiers and snowboarders. It is often found in the Rocky Mountains of North America and in Niseko, Japan.
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The textures of a snowdrift on the Long Mynd, Shropshire
Slush
Snow which partially melts upon reaching the ground, to the point that it accumulates in puddles of partially-frozen water.
Snowdrift
Large piles of snow which occur near walls and curbs, as the wind tends to push the snow up toward the vertical surfaces.
Watermelon snow
A reddish/pink colored snow that smells like watermelons, and is caused by a red colored green algae called chlamydomonas nivalis

See also

References

1. ^ Klesius, Michael (2007), "The Mystery of Snowflakes", National Geographic 211(1): 20, ISSN 0027-9358
2. ^ [1]
3. ^ [2]
4. ^ [3]
5. ^ [4]
6. ^ [5]

External links

Arthur George Owens (died 1976) was a Welsh electrical engineer who acted as a double agent during World War II. He was working for MI5 while appearing to the Abwehr (the German intelligence agency) to be one of their agents. Owens was known to MI5 by the codename 'SNOW'.
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Lund University (Swedish: Lunds universitet), located in Lund in southernmost Sweden, is one of Sweden's most prestigious universities[2] and Scandinavia's largest institution for education and research[3]
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For other uses, see nessie (disambiguation).


NESSIE (New European Schemes for Signatures, Integrity and Encryption) was a European research project funded from 2000–2003 to identify secure cryptographic primitives.
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finite state machine (FSM) or finite state automaton (plural: automata) or simply a state machine is a model of behavior composed of a finite number of states, transitions between those states, and actions.
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eSTREAM is a project to identify "new stream ciphers that might become suitable for widespread adoption", organised by the EU ECRYPT network. It was set up as a result of the failure of all six stream ciphers submitted to the NESSIE project.
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stream cipher is a symmetric cipher where plaintext bits are combined with a pseudorandom cipher bit stream (keystream), typically by an exclusive-or (xor) operation. In a stream cipher the plaintext digits are encrypted one at a time, and in which the transformation of successive
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A5/1 is a stream cipher used to provide over-the-air communication privacy in the GSM cellular telephone standard. It was initially kept secret, but became public knowledge through leaks and reverse engineering. A number of serious weaknesses in the cipher have been identified.
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A5/2 is a stream cipher used to provide voice privacy in the GSM cellular telephone protocol.

The cipher is based around a combination of four linear feedback shift registers with irregular clocking and a non-linear combiner.
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E0 is a stream cipher used in the Bluetooth protocol. It generates a sequence of pseudorandom numbers and combines it with the data using the XOR operator. The key length may vary, but is generally 128 bits.
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FISH (FIbonacci SHrinking) stream cipher is a fast software based stream cipher using Lagged Fibonacci generators, plus a concept from the shrinking generator cipher. It was published by Siemens in 1993. FISH is quite fast in software and has a huge key length.
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In computer cryptography, Grain is a stream cipher designed for restricted hardware environments and submitted to eSTREAM in 2004 by Martin Hell, Thomas Johansson and Willi Meier. It has been selected as Phase 2 Focus Candidate for Profile 2 by the eSTREAM project.
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HC-256 is a stream cipher designed to provide bulk encryption in software at high speeds while permitting strong confidence in its security. Designed by Hongjun Wu, it is an eSTREAM cipher candidate and has been selected as a Profile 1, Phase 3 Focus candidate. It is not patented.
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In cryptography, ISAAC is a pseudorandom number generator and a stream cipher designed by Robert Jenkins (1996) to be cryptographically secure. The name is an acronym for Indirection, Shift, Accumulate, Add, and Count.
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LILI-128 is an LFSR based synchronous stream cipher with a 128-bit key. On 13 November 2000, LILI-128 was presented at the NESSIE workshop. It is designed to be simple to implement in both software and hardware.
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In cryptography, MUGI is a pseudorandom number generator (PRNG) designed for use as a stream cipher. It has been recommended for Japanese government use by the CRYPTREC project.

MUGI takes a 128-bit secret key and a 128-bit initial vector (IV).
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For other uses, see Panama (disambiguation).


Panama is a cryptographic primitive which can be used both as a hash function and a stream cipher.
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Phelix is a high-speed stream cipher with a built-in single-pass message authentication code (MAC) functionality, submitted in 2004 to the eSTREAM contest by Doug Whiting, Bruce Schneier, Stefan Lucks, and Frédéric Muller.
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The Pike stream cipher was invented by Ross Anderson to be a "leaner and meaner" version of FISH after he broke FISH in 1994; the name is a humorous allusion to the Pike fish. The cipher combines ideas from A5 with the Lagged Fibonacci generators used in FISH.
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Py is a stream cipher submitted to eSTREAM by Eli Biham and Jennifer Seberry. It is one of the fastest eSTREAM candidates at around 2.6 cycles per byte on some platforms. It has a structure a little like RC4, but adds an array of 260 32-bit words which are indexed using a
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Rabbit is a high-speed stream cipher first presented[1] in February 2003 at the 10th FSE workshop. In May 2005, it was submitted to the eSTREAM project of the ECRYPT network.
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RC4 (also known as ARC4 or ARCFOUR) is the most widely-used software stream cipher and is used in popular protocols such as Secure Sockets Layer (SSL) (to protect Internet traffic) and WEP (to secure wireless networks).
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Salsa20 is a stream cipher submitted to eSTREAM by Daniel Bernstein. It is built on a pseudorandom function based on 32-bit addition, bitwise addition (XOR) and rotation operations, which maps a 256-bit key, a 64-bit nonce, and a 64-bit stream position to a 512-bit output; this
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The Scream cipher is a word-based stream cipher developed by Shai Halevi, Don Coppersmith and Charanjit Jutla from IBM.

The cipher is designed as a software efficient stream cipher. The authors describe the goal of the cipher to be a more secure version of the SEAL cipher.
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SEAL (Software-Optimized Encryption Algorithm) is a very fast stream cipher optimised for machines with a 32-bit word size and plenty of RAM.

The first version was published by Phillip Rogaway and Don Coppersmith in 1994. The current version, published in 1997, is 3.0.
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Sober may refer to:
  • Sobriety, the state of being sober, and not under the influence of alcohol or other drugs
  • Sober (computer worm), a variety of computer worm
  • Sober space, a type of sobriety of a topological space in mathematics
  • Sôber, a Spanish rock band

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SOBER-128 is a synchronous stream cipher designed by Hawkes and Rose (2003) and is a member of the SOBER family of ciphers. SOBER-128 was also designed to provide MAC (Message authentication code) functionality.
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SOSEMANUK is a synchronous stream cipher developed by Come Berbain, Olivier Billet, Anne Canteaut, Nicolas Courtois, Henri Gilbert, Louis Goubin, Aline Gouget, Louis Granboulan, Cédric Lauradoux, Marine Minier, Thomas Pornin and Hervé Sibert.
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Trivium is a synchronous stream cipher designed to provide a flexible trade-off between speed and gate count in hardware, and reasonably efficient software implementation.
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vest is a type of collarless sleeveless upper-body garment. There are a variety of similar garments that may be referred to as vests, but also under other names in different regions.
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In cryptography, WAKE is a stream cipher designed by David Wheeler in 1993.

WAKE stands for Word Auto Key Encryption. The cipher works in cipher feedback mode, generating keystream blocks from previous ciphertext blocks.
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