olemus
krüptovõtme sihilikult arvutusmahukas teisendus
jõuründe raskendamiseks
= a resource-intensive conversion of cryptographic key as a countermeasure to brute.force attacks

https://stackoverflow.com/questions/12152864/key-stretching-vs-key-stengthening

vt ka
https://en.wikipedia.org/wiki/Key_derivation_function