Shannon theorem of perfect secrecy

Theorem

In any perfectly secure encryption scheme, $\lvert \mathcal{K} \rvert \geq \lvert \mathcal{M} \rvert$ .

Proof

#incomplete

References

1. https://crypto.stackexchange.com/questions/34048/shannon-theorem-of-perfect-secrecy
2. https://github.com/cpeikert/TheoryOfCryptography/blob/master/lec02 - Computational Hardness.pdf