A marker trait used to indicate that an RngCore or BlockRngCore
implementation is supposed to be cryptographically secure.
Cryptographically secure generators, also known as CSPRNGs, should
satisfy an additional properties over other generators: given the first
k bits of an algorithm’s output
sequence, it should not be possible using polynomial-time algorithms to
predict the next bit with probability significantly greater than 50%.
Some generators may satisfy an additional property, however this is not
required by this trait: if the CSPRNG’s state is revealed, it should not be
computationally-feasible to reconstruct output prior to this. Some other
generators allow backwards-computation and are consided reversible.
Note that this trait is provided for guidance only and cannot guarantee
suitability for cryptographic applications. In general it should only be
implemented for well-reviewed code implementing well-regarded algorithms.
Note also that use of a CryptoRng does not protect against other
weaknesses such as seeding from a weak entropy source or leaking state.