Valor medio
ponderado de la cantidad de información transmitida por un mensaje, no conocido
a priori, de una fuente (conjunto) de ellos.
En otras
palabras, la entropía de una fuente mide la incertidumbre que, a priori, tiene
un observador acerca de la aparición de un mensaje (no conocido previamente) de
dicha fuente.
Se mide en
bitios y, raramente, en Hartleys (en honor del matemético estadounidense R.V.
Hartley, uno de los primeros estudiosos de la teoría de la información).
[Ribagorda:1997]
Medida de la
impredictibilidad. Se dice que una contraseña tiene mayor entropía cuanto más
impredecible sea. Y
viceverse, una contraseña fácilmente predecible tiene poca entropía.
A measure of the
amount of uncertainty that an Attacker faces to determine the value of a
secret. Entropy is usually stated in bits. [NIST-SP800-63:2013]
A measure of the
difficulty that an Attacker has to guess the average password used in a system.
In this document, entropy is stated in bits. When a password has n-bits of
guessing entropy then an Attacker has as much difficulty guessing the average
password as in guessing an n-bit random quantity. The Attacker is assumed to
know the actual password frequency distribution. [NIST-SP800-63:2013]
A measure of the
difficulty that an Attacker has to guess the most commonly chosen password used
in a system. In this document, entropy is stated in bits. When a password has
n-bits of min-entropy then an Attacker requires as many trials to find a user
with that password as is needed to guess an n-bit random quantity. The Attacker
is assumed to know the most commonly used password(s). [NIST-SP800:63:2013]
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