Cipher Challenge
My first Gronsfeld
This is a Gronsfeld cipher: a repeating sequence of digits applies Caesar shifts, one digit per position. Use Repeated sequences and their spacings to propose the digit-string length, then open Periodic columns with that period. In each column, compare a likely plaintext letter with its ciphertext letter and calculate the backward Caesar shift. A valid Gronsfeld Key digit is only 0 through 9, so reject guesses that require a larger shift. Assemble the surviving digits in column order, enter them in Gronsfeld transform, choose Decrypt, and Run. Revise individual digits when errors recur at one periodic position, or reconsider the period when the whole Result remains incoherent. Submit the complete readable text.
Ciphertext
Ipv ztdu oiyy Puprtknoe, vfrnpcis yqdu xij ahqibyrqh Ofd lroxbnwv emhncv, osu fusiecjc ofxujav. Fedm mlhmu xdsqpjjb d Defxju tljkc issn enup xiwxxhl onwh, xljhq viesuub mmnncv ulf hjqemefcht jpw nyfvz unujsenl fppvrw. Xti sjyhbxfi-bhryfslh ttbhrqhw ut nvumnfch ulf Pnb miolck, ulfs bsmmu yqh dmqmnuuiyy kb ulby yhsmpi. Lrntbwn isirznqu wzrkrmw pw j vuvpsp fsmc brwi pjpnoz tmfrquiyy uhuxfwb doh dfufvpbyn wii cflnxesi bkjju. Irvdesi jqz tstyrtem wntvmsnwj b zbqdh bfpan qjrf. Wjql xij ahnejsrqh hjlrw deoirgbxfx jqe xfxc wiin flupwt yqh xlpqn fppvrw. Uftffche hjlrwt esj jomsxjm, doh ajar jw njjqjrhkdo, jrdqdgjrh fc wii cjplorjsp rg e Ljh. Lg iswxut vfhdu bx psn spwjyrro mo jehsc ddlof, vfarvf xifc gjkjy. Ri ulf wnfpzfwng emhncv siqjjw b witawfv qfcwfvo, ynvu xij bkpvuja sfvjtm. Gp rpy cubrtqjwf xij mlhmux rqus mjcwfvt ta dqtmd oxmp Wnphoèvf xqlgxt. Pnhq iohabqxjtw doh ejluztunxq emsjlwjsox bwsejlqw, bre anujjz jehsc qjalphjh lrmyns khgssj jfdiqyrqh e sjjgbfmj ahtymy.