Full entropy

In cryptography, full entropy is a property of an output of a random number generator. 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).^[1]

The term is extensively used in the NIST random generator standards NIST SP 800-90A and NIST SP 800-90B. With full entropy, the per-bit entropy in the output of the random number generator is close to one: ${\displaystyle 1-\epsilon }$, where per NIST a practical ${\displaystyle \epsilon <2^{-32}}$.^[1]

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.^[2]