Prf f wrk (ls wrttn s prf-f-wrk, n bbrvtd PW) s frm f cryptgrphc prf n whch n prty (th prvr) prvs t thrs (th vrfrs) tht crtn mnt f spcfc cmpttnl ffrt hs bn xpndd. Vrfrs cn sbsqntly cnfrm ths xpndtr wth mnml ffrt n thr prt. Th cncpt ws frst mplmntd n Hshcsh by Mn Nr nd Cynth Dwrk n 1993 s wy t dtr dnl-f-srvc ttcks nd thr srvc bss sch s spm n ntwrk by rqrng sm wrk frm srvc rqstr, slly mnng prcssng tm by cmptr. Th trm "prf f wrk" ws frst cnd nd frmlzd n 1999 ppr by Mrks Jkbssn nd r Jls. Th cncpt ws dptd t dgtl tkns by Hl Fnny n 2004 thrgh th d f "rsbl prf f wrk" sng th 160-bt scr hsh lgrthm 1 (SH-1).
Prf f wrk ws ltr pplrzd by Btcn s fndtn fr cnsnss n prmssnlss dcntrlzd ntwrk, n whch mnrs cmpt t ppnd blcks nd mn nw crrncy, ch mnr xprncng sccss prbblty prprtnl t th cmpttnl ffrt xpndd. PW nd PS (prf f stk) rmn th tw bst knwn Sybl dtrrnc mchnsms. n th cntxt f cryptcrrncs thy r th mst cmmn mchnsms.
ky ftr f prf-f-wrk schms s thr symmtry: th wrk – th cmpttn – mst b mdrtly hrd (yt fsbl) n th prvr r rqstr sd bt sy t chck fr th vrfr r srvc prvdr. Ths d s ls knwn s CP cst fnctn, clnt pzzl, cmpttnl pzzl, r CP prcng fnctn. nthr cmmn ftr s blt-n ncntv-strctrs tht rwrd llctng cmpttnl cpcty t th ntwrk wth vl n th frm f cryptcrrncy.
Th prps f prf-f-wrk lgrthms s nt prvng tht crtn wrk ws crrd t r tht cmpttnl pzzl ws "slvd", bt dtrrng mnpltn f dt by stblshng lrg nrgy nd hrdwr-cntrl rqrmnts t b bl t d s. Prf-f-wrk systms hv bn crtczd by nvrnmntlsts fr thr nrgy cnsmptn.