 In complexity-based modern cryptography, a security scheme is
"provably secure" if the probability of security failure (e.g.,
inverting a one-way function, distinguishing cryptographically strong pseudorandom bits from truly random bits) is negligible in terms of the input formula_15 = cryptographic key length formula_28.Hence comes the definition at the top of the page because key length formula_28 must be a natural number.Nevertheless, the general notion of negligibility doesn't require that the input parameter formula_15 is the key length formula_28.