  Common random string model is a popular model in classical cryptography with
many constructions proposed in this model. We study a quantum analogue of this
model called the common Haar state model, which was also studied in an
independent work by Chen, Coladangelo and Sattath (arXiv 2024). In this model,
every party in the cryptographic system receives many copies of one or more
i.i.d Haar states.
  Our main result is the construction of a statistically secure PRSG with: (a)
the output length of the PRSG is strictly larger than the key size, (b) the
security holds even if the adversary receives
$O\left(\frac{\lambda}{(\log(\lambda))^{1.01}} \right)$ copies of the
pseudorandom state. We show the optimality of our construction by showing a
matching lower bound. Our construction is simple and its analysis uses
elementary techniques.
