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== '''[[Block cipher]]''' ==
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In [[cryptography]], '''block ciphers''' are one of the two main types of [[symmetric cipher]]; they operate on fixed-size blocks of [[plaintext]], giving a block of [[ciphertext]] for each. The other main type are [[stream cipher]]s, which generate a continuous stream of keying material to be mixed with messages.
==Footnotes==
 
The basic function of block ciphers is to keep messages or stored data [[Information_security#Content_confidentiality | secret]]; the intent is that an unauthorised person be completely unable to read the enciphered material. Block ciphers therefore use a [[Key (cryptography)|key]] and are designed to be hard to read without that key. Of course an attacker's intent is exactly the opposite; he wants to read the material without authorisation, and often without the key. See [[cryptanalysis]] for his methods.
 
Among the best-known and most widely used block ciphers are two US government standards. The [[Data Encryption Standard]] (DES) from the 1970s is now considered obsolete; the [[Advanced Encryption Standard]] (AES) replaced it in 2002. To choose the new standard, the [[National Institute of Standards and Technology]] ran an AES competition. Fifteen ciphers were entered, five finalists selected, and eventually AES chosen. Text below gives an overview; for details of the process and the criteria, and descriptions of all fifteen candidates, see the [[AES competition]] article.
 
These standards greatly influenced the design of other block ciphers, and the latter part of this article is divided into sections based on that. [[#DES and alternatives | DES and alternatives]] describes 20th century block ciphers, all with the 64-bit block size of DES. [[#The AES generation | The AES generation]] describes the next generation, the first 21st century ciphers, all with the 128-bit block size of AES. [[#Large-block ciphers | Large-block ciphers]] covers a few special cases that do not fit in the other sections.
 
 
''[[Block cipher|.... (read more)]]''
 
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Latest revision as of 09:19, 11 September 2020

After decades of failure to slow the rising global consumption of coal, oil and gas,[1] many countries have proceeded as of 2024 to reconsider nuclear power in order to lower the demand for fossil fuels.[2] Wind and solar power alone, without large-scale storage for these intermittent sources, are unlikely to meet the world's needs for reliable energy.[3][4][5] See Figures 1 and 2 on the magnitude of the world energy challenge.

Nuclear power plants that use nuclear reactors to create electricity could provide the abundant, zero-carbon, dispatchable[6] energy needed for a low-carbon future, but not by simply building more of what we already have. New innovative designs for nuclear reactors are needed to avoid the problems of the past.

(CC) Image: Geoff Russell
Fig.1 Electricity consumption may soon double, mostly from coal-fired power plants in the developing world.[7]

Issues Confronting the Nuclear Industry

New reactor designers have sought to address issues that have prevented the acceptance of nuclear power, including safety, waste management, weapons proliferation, and cost. This article will summarize the questions that have been raised and the criteria that have been established for evaluating these designs. Answers to these questions will be provided by the designers of these reactors in the articles on their designs. Further debate will be provided in the Discussion and the Debate Guide pages of those articles.

Footnotes
  1. ↑ Global Energy Growth by Our World In Data
  2. ↑ Countries, organizations, and public figures that have reconsidered their stance on nuclear power are listed on the External Links tab of this article.
  3. ↑ Pumped storage is currently the most economical way to store electricity, but it requires a large reservoir on a nearby hill or in an abandoned mine. Li-ion battery systems at $500 per KWh are not practical for utility-scale storage. See Energy Storage for a summary of other alternatives.
  4. ↑ Utilities that include wind and solar power in their grid must have non-intermittent generating capacity (typically fossil fuels) to handle maximum demand for several days. They can save on fuel, but the cost of the plant is the same with or without intermittent sources.
  5. ↑ Mark Jacobson believes that long-distance transmission lines can provide an alternative to costly storage. See the bibliography for more on this proposal and the critique by Christopher Clack.
  6. ↑ "Load following" is the term used by utilities, and is important when there is a lot of wind and solar on the grid. Some reactors are not able to do this.
  7. ↑ Fig.1.3 in Devanney "Why Nuclear Power has been a Flop"

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