Full entropy

In cryptography, full entropy is a property of an output of a <a href="/facts/Random_number_generator/RtXEfbzd">random number generator</a>. The output has full entropy if it cannot practically be distinguished from an output of a theoretical perfect random number source (has almost n bits of entropy for an n-bit output).
The term is extensively used in the <a href="/facts/NIST/gr9Fnh85">NIST</a> random generator standards <a href="/facts/NIST_SP_800-90A/oSrLj7wX">NIST SP 800-90A</a> and <a href="/facts/NIST_SP_800-90B/8hCL5kC0">NIST SP 800-90B</a>. With full entropy, the per-bit entropy in the output of the random number generator is close to one: 
 
 
 
 1
 −
 ϵ
 
 
 {\displaystyle 1-\epsilon }
 
, where per NIST a practical 
 
 
 
 ϵ
 <
 
 2
 
 −
 32
 
 
 
 
 {\displaystyle \epsilon <2^{-32}}
 
.
Some sources use the term to define the ideal random bit string (one bit of entropy per bit of output). In this sense, "getting to 100% full entropy is impossible" in the real world.

Full entropy open-in-new

Full entropy