Average Case Hardness

Hardness of a computational problem on a natural random input distribution, as opposed to worst-case hardness.

Status	Statement	Tags
	Planted-Subgraph Character Sum The source derives the formula governing low-degree detection of a planted subgraph, observes the character sum in it should be small for most graphs, and says it leaves the rigorous study of the question to future work. No bound is proved and none is stated as a target. 5 open	Average Case Hardness Planted Subgraph Problemslower-boundadaptation (ai)
	Planted k-OV Hardness Conjecture 10 of the source, and a newly proposed average-case assumption rather than a question the literature already asked. Its worst-case counterpart – that k-OV requires n^(k-o(1)) time – is a central conjecture of fine-grained complexity. The planting preserves the marginal distribution of any subset of fewer than k vectors, and the source gives a search-to-decision reduction. 5 open	Average Case Hardness Fine Grained Cryptography Orthogonal Vectors Planted Constraint Satisfactionassumption
	Sub-log Share Size for 2-out-of-n The information-theoretic share size is exactly log n and Shamir’s scheme matches it. The source proves a (1/5) log log n lower bound for the computational setting with public information, leaving a log n versus log log n gap, and proves that beating log n by any constant factor is equivalent to a concrete planted clique-and-independent-set problem. 4 open	Average Case Hardness Planted Subgraph Problems Threshold Secret Sharingtight-bound
	SBP Collision Resistance Posed as a displayed Open Question and called a central open challenge. The source gives an efficient online collision finder for small kappa and an overlap-gap-based online lower bound for a different, randomized activation – introduced precisely because the SBP’s own collision space resists a first-moment analysis. For very large kappa collisions become trivial. The middle window is reached by neither technique. 4 open	Average Case Hardness Collision Resistant Hashing Overlap Gap Property Planted Constraint Satisfactionseparation
	No expanding weak quadratic PRGs Open: whether every family of quadratic Λ(n)-bounded polynomials at stretch m ≥ n^{1+ε} admits an efficient distinguisher from the same evaluations plus bounded independent noise; the paper proves only the i.i.d.-nice special case (Theorem 2) and reports, without proof, that no degree-two candidate survives its attacks experimentally. 3 open	Average Case Hardness Pseudorandom Generatorsimpossibility
	No Self-Reduction for LSN Conjecture 5.20 of the source. It proves no random self-reduction exists from an arbitrary worst-case QNCP instance into LSN, naming exchange symmetry between code and error as the obstruction, and proves the tableau-randomizing barrier conditionally on the scrambling gap being polynomially related to eps. It is explicit that this is not an impossibility for random self-reductions in general. 4 open	Average Case Hardness Learning Parity With Noise Quantum Information Stabilizer Codesimpossibilityadaptation (ai)
	Blockwise-random quadratic recovery Open: whether there is a polynomial-time algorithm that provably recovers the planted input from m = n^{1+eps} published quadratics of the blockwise-random (Lin-Matt) form, sum of a random sparse (perfect-matching) part and an independent random dense part. The paper proves this for i.i.d.-nice polynomial distributions (Theorem 2) but the blockwise-random distribution is not nice, and reports only experimental recovery via a modified semidefinite program. 5 open	Average Case Hardness Pseudorandom Generatorsassumption
	PKE from constant-noise planted k-XOR Open: whether public-key encryption can be based on the hardness of planted k-XOR with a linear number of equations and a constant noise rate, as a single assumption. The survey poses it as one of two closing open questions and does not return to it; every combinatorial scheme it surveys needs sub-constant noise.	Average Case Hardness Planted Constraint Satisfactionseparationbarrier (ai)
	RM Gap to Capacity for BEC Conjecture 14 of the source. That Reed-Muller codes achieve capacity for the BEC is a theorem of Kudekar et al.; the gap to capacity – a polynomial rate of convergence – is open. The source needs it to strengthen its refutation of the expansion-implies-hardness conjecture for noisy k-XOR from quasi-polynomially many constraints to polynomially many, and notes the question was raised explicitly in three prior works. 4 open	Average Case Hardness Code Based Cryptography Expander Graphs Reed Solomon Codestight-bound
	Certifying no small non-expanding set Open: whether the non-existence of a small non-expanding set in a random unbalanced bipartite graph admits a nondeterministic certificate that is sound and complete on average, at the parameters the ABW cryptosystem uses. The survey poses it as one of two closing open questions, takes no position, and does not return to it.	Average Case Hardness Expander Graphsseparation
	Binary dual-distance bound is the worst case Open, and asserted rather than asked – the source writes that it expects the inequality, gives an intuition covering one of the two competing effects, records that all prior work assumes it, and proves nothing. A probe at small parameters is consistent with it; the parameters the source’s own construction uses are out of computational reach, which is why the source does not check it either. 7 open	Average Case Hardness Dual Distance Learning Parity With Noiselower-boundadaptation (ai)
	CHV Online Threshold Conjecture 1 of the source, its online threshold conjecture. The source gives an online algorithm achieving kappa = O(sqrt(alpha)/B) and an overlap-gap argument against stable algorithms; the conjecture pins the constant sqrt(pi/8) as the exact place where online algorithms stop. Separately it proves, under worst-case lattice hardness, that no polynomial-time algorithm solves CHV for kappa = O(1/(B n^(1/2+eps))). 4 open	Average Case Hardness Collision Resistant Hashing Locality Preserving Hashing Overlap Gap Propertytight-bound