What is an avalanche effect?

Avalanche effect is a term from cryptography that describes behaviour of a special kind of math functions.

Even a slight change in an input string should cause the hash value to change drastically. A Hash Function is a transformation that takes a variable length bit sequence (Message) and produces a fixed length bit sequence (Message Digest). Even if 1 bit is flipped in the input string, at least half of the bits in the hash value will flip as a result. This is called an avalanche effect.

Since it is computationally infeasible to produce a document that would hash to a given value or find two documents that hash to the same value, a document's hash can serve as a cryptographic equivalent of the document. This makes a one-way hash function a central notion in public-key cryptography. When producing a digital signature for a document, we no longer need to encrypt the entire document with a sender's private key (which can be extremely slow). It is sufficient to encrypt the document's hash value instead.

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