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Probably a Code?

Is the regularity shown in this encoded message noise or structure?

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Stage 5 Cipher Challenge

Can you crack these very difficult challenge ciphers? How might you systematise the cracking of unknown ciphers?

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More Secret Transmissions

In 'Secret Transmissions', Agent X could send four-digit codes error free. Can you devise an error-correcting system for codes with more than four digits?

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Stage: 5 Challenge Level: Challenge Level:3 Challenge Level:3 Challenge Level:3

Xn nwj kpv gmpl ipxa, lmat swcm! Ipxa hwgb dn rqeptz xa riattl p xdtniaxwiqmiqr kxxwmg. Ndz tfpuetta aqzm ipxa dvt exbw i zmnedzs wu ttvvbw blw, xb'h xdahqqtt bd adtkm xb qg wicl ychb iznqco ewhaxjxtxbxmh. Pdetdtz, lqip p tdvvmg stglwgl ipxa vmia kmgg wigl. Iptzt igm bwgm hwepxaiqriims btkwvxyjmh, wcm dn lpxkw qh kptams Spaxazq tfpuxvpbxwc. Bwqh qcddtkmh tdwzqco uwg ztxtiims ttbimga xv ipt kxxwmgbtfi. Qi'a aqzmag ippb ipt vjuqmg wu ttbimga xvqmietmc bwmhm gmempbh qh i bcabxxam dn ipt stglwgl amcoip. Awds pb lqzqemsqp ndz bwgm xvuwgupbxwc! Jn bwm lin, qu gdc sqsv'i edzz qi wjb, ipt xgmkqdch kxxwmg epa p stglwgl hcqaiqiciqdv rqeptz lqip zmnedzs stglwgl. Hw uig, et'dt wctn kdvhqsmgms ajjhbxbjbxwc kxxwmga, qci bwmgm pzt wiptz ptimgvpbxdta. Lm rwjts ndz tfpuett ztwgltz ipt kxxwmgbtfi.