Avalanche effect

In cryptography, the avalanche effect is the desirable property of cryptographic algorithms, typically block ciphers[1] and cryptographic hash functions, wherein if an input is changed slightly (for example, flipping a single bit), the output changes significantly (e.g., half the output bits flip).

The actual term was first used by Horst Feistel,[1] 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, being given only the output.

Thus, the avalanche effect is a desirable condition from the point of view of the designer of the cryptographic algorithm or device.

The SAC builds on the concepts of completeness and avalanche and was introduced by Webster and Tavares in 1985.