A simple cipher

[Mr.Cipher]

Can you decode this? It might be very important!

Tl jy slln eqbfkn Aivfhlog Rtfqk,

Alw iqf tabksr wbta ylu? Br taf gkff rtbhh mhiybks um?

B wir nfhbsatfn tl qfin yluq jlrt qfofkt frriy lk taf Lrmqfy Fvlhutblk Iqjluq. Ir ihwiyr, yluq oljjfktr iqf bkrbsateuh ikn talusat-mqlvlgbks. Alwfvfq, B ebkn lkf lq twl mlbktr le bkioouqioy tait ylu jiy wbra tl olqqfot cfelqf muchboitblk.

Ebqrthy, taf oaiksbks ittbtunfr tlwiqnr aujik oljcitiktr nbn klt bk iky wiy bkehufkof taf nfobrblkr hfinbks tl taf nfoljjbrrblkbks le taf Fvlhutblk iqjluq. Qitafq, taf tfoakboih hbjbtitblkr le taf iqjluq btrfhe wfqf tl chijf.

Rfolknhy, taf vbqur lutcqfig tait hfn tl taf qfnfrbsk le taf rubt'r ebqjwiqf nbn bk eiot hfin tl rfvfqih aujik oiruihtbfr; tabr br uknloujfktfn, cut B rmfig eqlj mfqrlkih fxmfqbfkof.

I wlqn le wiqkbks; taf rubtr wfqf klt ir qfvlhutblkiqy lq ir klchf ir ylu irrujf. Taf ivfqisf jbhbtiqy cuee jbsat raiqf yluq vbfwmlbkt, cut yluq ukfnbtfn frriy bk taf aiknr le ik fxmfqbfkofn rlhnbfq eqlj taf mfqbln br hbgfhy tl mqlvlgf leefkrf.

Yluqr rbkofqfhy,

-Olqmlqih Mukbrajfkt

MR: B rfkt tabr vbi i kfw jfrrfksfq; wait aimmfkfn tl taf hirt lkf wir jlrt ukelqtukitf.
​ Its a letter to a museum curator, from Corporal Punishment.Can you please solve this?

[nana77]

The real challenge was figuring out how to use notepad to solve it. And then fixing the capitalization.

To my good friend Havelock Stern,

How are things with you? Is the knee still playing up?

I was delighted to read your most recent essay on the Osprey Evolution Armour. As always, your comments are insightful and thought-provoking. However, I find one or two points of inaccuracy that you may wish to correct before publication.

Firstly, the changing attitudes towards human combatants did not in any way influence the decisions leading to the decommissioning of the evolution armour. Rather, the technical limitations of the armour itself were to blame.

Secondly, the virus outbreak that led to the redesign of the suit's firmware did in fact lead to several human casualties; this is undocumented, but i speak from personal experience.

A word of warning; the suits were not as revolutionary or as noble as you assume. The average military buff might share your viewpoint, but your unedited essay in the hands of an experienced soldier from the period is likely to provoke offense.

Yours sincerely,

-Corporal Punishment

PS: I sent this via a new messenger; what happened to the last one was most unfortunate.

[phil1882]

beat me to it, was about half way through solving this one.

[nana77]

I did a spoiler, you can still finish.

[Yoruichi-san]

is that the cipher key is (hyphens in for letters not used):

ICONFESAB-GHJKLM-QRTUVWXY-

i.e. "I confess" and then the rest of the alphabet as is. That and the mysterious content of the message are reminiscent of puzzle competition type puzzles and suggest to me there might be a deeper puzzle. (or maybe it's from a video game or sth and I'm reading too much into it lol)