# Term:Entropy

## NIST IR 7298

Entropy - A measure of the amount of uncertainty that an attacker faces to determine the value of a secret. SOURCE: SP 800-63

## NIST SP 800-22r1

Entropy - A measure of the disorder or randomness in a closed system. The entropy of uncertainty of a random variable X with probabilities pi, …, pn is defined to be H(X) = .

## NIST SP 800-63v1.0.2

Entropy - A measure of the amount of uncertainty that an attacker faces to determine the value of a secret. Entropy is usually stated in bits. See Appendix A.

## NIST SP 800-90

Entropy - A measure of the disorder, randomness or variability in a closed system. The entropy of X is a mathematical measure of the amount of information provided by an observation of X. As such, entropy is always relative to an observer and his or her knowledge prior to an observation. Also, see min- entropy.