The term ‘Avalanche effect’ was given by a German-American cryptographer Horst Feistel. ‘Cryptography’ is a term used to denote the secure communication held between people in encrypted form so that it may not be understood by any other person. In cryptography, the avalanche effect is a special property of cryptographic sequences or instructions (typically called ‘Block Ciphers’ and ‘Cryptographic Hash’ functions) wherein the output changes significantly even if the input is changed very slightly.


A ‘block cipher’ as the name shows, block something; they are the ones that encrypt and decrypt the input as well as the output respectively which contains sensitive information that should not reach the normal public. If any input is changed even slightly, the output in cases shows a significantly large change. If we talk about the high-quality block ciphers, even a very small change in the main or the normal text would cause a very drastic change in the ciphertext.

If a block cipher or a cryptographic hash does not exhibit this avalanche effect to a desired degree as required, then it has a poor effect and thus a Cryptanalyst (who study or analyze information system to study the hidden sides of the system) can make predictions about what the input was; just in case they are given only the output. This is just enough to break the code and analyze what the information was, partially or completely, and this, in turn, results in the breaking of the algorithm. Thus, the avalanche effect is a desirable condition as seen from the point of view of any designer of the cryptographic algorithm in any device. This is because the Cryptography tends to protect the very sensitive information and when sending it from the sender to the receiver, the information is encrypted so that if it goes in the hands of any undesirable person, they may not use the information for the harmful purpose by easily understanding it.


To do the Cryptography, one main thing is to construct such a device that can code and decode sensitive information. This can be done by the construction of cipher or hash. The construction of a cipher or hash to exhibit the desired avalanche effect is one of the most primary design objectives. If we study this effect mathematically the construction works on the principle and takes advantage of the butterfly effect. the butterfly effect is a very sensitive dependence on the initial conditions where a small change initially can bring a very large change later on. That is why most block ciphers and hash functions have large data blocks. Both of these features block the data to be read by an unauthorized person and allow small changes to transfer rapidly with the help of the repetitions of the algorithm, such that every small bit of the output should depend on every small bit of the input and both the output and the input should be in the correct order before the algorithm terminates or stops.

In a sense of cryptography, the avalanche effect is a term that is usually associated to show a specific behavior of the mathematical functions used for encryption or coding of sensitive data. Avalanche effect is basically considered as one of the most desirable properties of any encryption data code or algorithm. As we already saw that even a slight change in either of the text should result in a significant change in the whole encrypted ciphertext, this function is termed as an avalanche effect.


Simply referring, an avalanche effect measures the effect of the ciphertext (coded or encrypted text) in relation to where a small change made in plain text or the main one. Even though this concept of avalanche effect was or the first time identified by Shannon and his property of confusion but still the credit for this term first goes to Horst Feistel. To establish a strong cipher or may it be cryptographic hash function, the avalanche effect should be considered as one of the major role play.

In the case of those codes, algorithms, or functions that use the hash value, even a small alteration in an input text should bring a drastic change in the hash value in the output. In other words, we can say that change in a single bit of the input should bring a big change in at least half of the bits in the output. If one questions as to what a good Encryption Algorithm means, then for being a good Encryption Algorithm should follow the rule of having upto or more than 50% of avalanche effect. It means it should show at least a 50% Avalanche effect.


The Avalanche effect completely ensures that an attacker or an unauthorized person may not easily predict what is written in the text through a normal analysis. An encryption algorithm that does not satisfies this property may allow the attacker to analyze the text easily. This also means that in such cases, if there is a slight change or a change in a single bit of the input, it might result in a change in only a single bit of the output, hence it makes it easy for the attacker to crack the encrypted text.


Hash functions play a very important role in modern cryptography. A very important and desirable feature of a good hash function is an avalanche effect in a current degree and non-corelation between the input and the output and thus helps the sensitive data by making it statistically indistinguishable and normally unrecognizable from any random person.

The Hash function usually produces a variety of hashes and also returns them in many multiple formats, therefore making it easy to study the different hash properties. A hash function also demonstrates the avalanche effect like above in which a flip in a single bit in the input tends to make a very large change in the output or a change of several bits in the output.

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