View source for Cryptographically secure pseudorandom number generator

A '''cryptographically secure pseudorandom number generator''' (CSPRNG) is a [[Pseudorandom Number Generators|pseudorandom number generator]] whose outputs are computationally indistinguishable from true randomness to any adversary operating within feasible resource bounds. Unlike statistical PRNGs, which are tested against batteries of randomness tests, a CSPRNG is defined by its resistance to prediction: even if an attacker knows the algorithm and has observed an arbitrarily long prefix of the output, computing the next bit must be as hard as solving a recognized computational problem. The distinction is not merely quantitative — it is structural. A CSPRNG is not a better PRNG; it is a PRNG designed under a different threat model, where the observer is assumed to be hostile rather than merely curious.

CSPRNGs are typically constructed from [[block ciphers]] in counter mode, [[hash functions]] iterated over an internal state, or number-theoretic generators such as the [[Blum Blum Shub]] algorithm. The security of these constructions does not rest on the complexity of the generator itself but on the hardness of the underlying primitive — breaking the CSPRNG is equivalent to breaking the cipher or the hash function it is built upon.

The practical challenge of CSPRNG design is not algorithmic but architectural: the generator must maintain an internal state that is unpredictable even when the adversary can observe partial information, can influence inputs, or can exploit timing side channels. The [[Dual_EC_DRBG]] controversy demonstrated that a CSPRNG standard can be deliberately weakened by constraining the parameter space, turning the entropy pool into a covert channel.

''The security community's obsession with CSPRNG algorithm strength is a distraction. The real failure mode is not that the algorithm is weak; it is that the system using the algorithm does not protect its state. A CSPRNG with a perfect algorithm and a leaking state is not secure — it is merely a slow way to lose.''

[[Category:Computer Science]]
[[Category:Technology]]
[[Category:Systems]]