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Encyclopedia > Avalanche effect
This article is about cryptography; for other meanings, see snowball effect.

In cryptography, the avalanche effect refers to a desirable property of cryptographic algorithms, typically block ciphers and cryptographic hash functions. The avalanche effect is evident if, when an input is changed slightly (for example, flipping a single bit) the output changes significantly (eg, half the output bits flip). In the case of quality block ciphers, such a small change in either the key or the plaintext should cause a drastic change in the ciphertext. The actual term was first used by Horst Feistel, although the concept dates back to at least Shannon's diffusion.


If a block cipher or cryptographic hash function does not exhibit the avalanche effect to a significant degree, then it has poor randomization, and thus a cryptanalyst can make predictions about the input given only the output. This may be sufficient to partially or completely break the algorithm. It is thus not a desirable condition -- at least from one point of view. Ciphers and hashes which do not exhibit an adequate avalanche effect exhibit patterns in their output, which cryptanalysis can often exploit.


Constructing a cipher or hash to exhibit a substantial avalanche effect is one of the primary design objectives. This is why most block ciphers are product ciphers. It is also why hash functions have large data blocks. Both these features allow small changes to propagate rapidly through iterations of the algorithm, such that every bit of the output should depend on every bit of the input before the algorithm terminates.


See also


Block ciphers edit  (http://en.wikipedia.org/w/index.php?title=Template:Block_ciphers&action=edit)
Algorithms: 3-Way | AES | Akelarre | Blowfish | Camellia | CAST-128 | CAST-256 | CMEA | DEAL | DES | DES-X | FEAL | FROG | G-DES | GOST | ICE | Iraqi | KASUMI | KHAZAD | Khufu and Khafre | LOKI89/91 | LOKI97 | Lucifer | MacGuffin | Madryga | MAGENTA | MARS | MISTY1 | MMB | NewDES | RC2 | RC5 | RC6 | REDOC | Red Pike | S-1 | SAFER | SEED | Serpent | SHACAL | SHARK | Skipjack | Square | TEA | Triple DES | Twofish | XTEA
Design: Feistel network | Key schedule | Product cipher | S-box | SPN   Attacks: Brute force | Linear / Differential cryptanalysis | Mod n | XSL   Standardisation: AES process | CRYPTREC | NESSIE   Misc: Avalanche effect | Block size | IV | Key size | Modes of operation | Piling_up lemma | Weak key

  Results from FactBites:
 
avalanche: Definition and Much More from Answers.com (5989 words)
Avalanches, which are natural forms of erosion and often seasonal, are usually classified by their content such as a debris or snow avalanche.
An avalanche is a slide of a large snow (or rock) down a mountainside, caused when a buildup of snow is released down a slope, and is one of the major dangers faced in the mountains in winter.
Avalanches occur when the load on the upper snow layers exceeds the bonding forces of a mass of snow (bonding to layer beneath, horizontal internal stability, support from anchors such as rocks and trees, stress support from top or bottom of slope).
Avalanche effect - Wikipedia, the free encyclopedia (401 words)
avalanche effect refers to a desirable property of cryptographic algorithms, typically block ciphers and cryptographic hash functions.
Constructing a cipher or hash to exhibit a substantial avalanche effect is one of the primary design objectives.
The Strict Avalanche Criterion (SAC) is a property of boolean functions of relevance in cryptography.
  More results at FactBites »

 
 

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