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PlayFair Code

OC OY FO LB VN PI AS AK OP VY GE SK OV MU FG UW ML NO OE DR NC FO RS OC VM TU UT YE RP FO LB VN PI AS AK OP VI VK YE OC NK OC CA RI CV VL TS OC OY TR FD VC VO OU EG KP VO OY VK TH ZS CV MB TW TR HP NK LR CU EG MS LN VL ZS CA NS CK OP OR MZ CK IZ US LC CV FD LV OR TH ZS CL EG UX MI FO LB IM VI VK IU AY VU UF VW VC CB OV OV PF RH CA CS FG EO LC KM OC GE UM OH UE BR LX RH EM HP BM PL TV OE DR NC FO RS GI ST HO GI LC VA IO AM VZ IR RL NI IW US GE WS RH CA UG IM FO RS KV ZM GC LB CG DR NK CV CP YU XL OK FY FO LB VC CK DO KU UH AV OC OC LC IU SY CR GU FH BE VK RO IC SV PF TU QU MK IG PE CE MG CG PG GM OQ US YE FV GF HR AL AU QO LE VK RO EO KM UQ IR XC CB CV MA OD CL AN OY NK BM VS MV CN VR OE DR NC GE SK YS YS LU UX NK GE GM ZG RS ON LC VA GE BG LB IM OR DP RO CK IN AN KV CN FO LB CE UM NK PT VK TC GE FH OK PD UL XS UE OP CL AN OY NK VK BU OY OD OR SN XL CK MG LV CV GR MN OP OY OF OC VK OC VK VW OF CL AN YE FV UA VN RP NC WM IP OR DG LO SH IM OC NM LC CV GR MN OP OY HX AI FO OU EP

FO RS appear 3 times in the passage. It could be ST OP.

OR also appears many times. It could also be S TO P.

OC also appears many times but it appeared in doubles (OC OC) so it cannot be part of STOP.

 

R T O R O T

P F S OR P S F

 

If the first one is the real keyword, then the square must be:

R TO

P FS

The second one cannot be the keyword because when the two letters are on the same row, the one to the immediate right is taken.

So, the square is R__TO

P__FS

 

<IP to DG>

<Is to DG>

So, now the square is R__TO or ____I

P__FS R__TO

____I P__FS

By trial and error, the second square is used.

 

<IP to DG>

<Is to pG>

 

So, the square can be G___I or ____I or ____I

R__TO R__TO R__TO

PD_FS G____ PD_FS

PD_FS G____

 

Trail and error shows that the second one would be the best.

 

<IM to DP>

<Is to ps>

 

This reveals the square:

____I

R__TO

G____

PDMFS

 

<rs to MZ>

<rs to pZ>

 

There are two choices: Z___I or ____I

R__TO R__TO

G____ G____

PDMFS PDMFS

Z____

 

By trail and error, the second one is used.

 

<OD to SN>

<Os to pN>

 

p* = SN. In Playfair, the encryption of * is always above or below P except in a special case.

 

*=the letter encrypted as N

 

Therefore, the square is now N___I

R__TO

G____

PDMFS

Z____

 

Now, there are no more clues to solve the key square, so assumption is used. The Playfair square is filled after with the rest of the alphabet in alphabetical order, so the last two letters should be X and Y.

 

N___I

R__TO

G____

PDMFS

Z__XY

 

<OC> appears very often, so it could stand for <TH>, the most common used two-letter part in English.

T and O appear on the same row, so this is one of the special cases where both the plaintext letter and the ciphertext letter appear on the same row. If this happens, then the letter to the right of the ciphertext letter would be used to encrypt. From that, the square is now:

N___I

RHCTO

G____

PDMFS

Z__XY

 

Again, there are no more clues, so we have to deduce plaintext letters by guessing.

 

<th is st LB VN> could be <th is st ag eN>

 

AG=LB

 

The only possible way is to have the two plaintext letters on one row, so the square becomes:

 

N___I

RHCTO

GBAL_

PDMFS

Z__XY

 

e*=VN In Playfair, the encryption of *, N, is always above or below e. But in this case, N is in the corner and the column under it is filled. So, this encryption must have been a special case, where the letter directly below the plaintext letter is used.

 

So, the square now looks like: N_EVI

RHCTO

GBAL_

PDMFS

Z__XY

 

<th is st ag ei sn AS>

 

According to the square, AS is an encryption of _M. If we fill it in, we get: this stage is n_m. It looks very much like: this stage is number six.

 

So, if the guess is correct, then the square is now:

 

N_EVI

RHCTO

GBALU

PDMFS

Z__XY

 

<th is st ag ei sn um AK rs ix>=THIS STAGE IS NUMBER SIX

 

AK=BE

 

In Playfair, the encryption of K is always above or below A and the encryption of A is always above or below K. There is only 1 place in the square that satisfies the conditions.

 

The square is now: NKEVI

RHCTO

GBALU

PDMFS

Z__XY

 

Now, only the letters Q and W are left.

 

<an di ti sa pl UW fa ir ci ph er>

 

It is probably: and it is a Playfair cipher.

 

AY=UW

 

Looking at the square, there is only one place where it can fit.

The square can now be completed:

 

NKEVI

RHCTO

GBALU

PDMFS

ZQWXY

 

DECODED TEXT:

th is st ag ei sn um be rs ix an di ti sa pl ay fa ir ci ph er st op th ef ol lo wi ng st ag ei sn um be rs ev en wi th in th ec on te xt of th is co mp et it io na nd it is en cr yp te da cx co rd in gt oa na df gv xt yp ec ip he rs to pw he ny ou at te mp tx to cr yp ta na ly se st ag es ev en yo uw il ls ex et ha ti ti sm or ec om pl ic at ed th an as tr ai gh tf or wa rd ad fg vx ci ph er st op un fo rt un at el yi ca nx no tg iv ey ou an ym or ec lu es st op ne wp ar ag ra ph in te rm so ft hi sx st ag et he sh ib bo le th th at yo us ho ul dt ak en ot eo fi sm ol yb de nu mn ew pa ra gr ap hy ou wi lx lp ro ba bl yh av en ot ic ed by no wt ha te ac hs ta ge is in ad if fe re nt ci ph er an di su su al ly in an ap pr op ri at el an gu ag es to ps ot he vi ge ne re st ag ew as in fr en ch an dt hi sp la yf ai rs ta ge is in en gl is hs to pi ft he pa tx te rn pe rs is ts th en th en ex ts ta ge wi lx lb ei ng er ma ns to pb ut do es th ep at te rn pe rs is tq ue st io nm ar kq

After removing ‘STOP', ‘NEW PARAGRAPH', extra letters and junk letters:

This stage is number six and it is a Playfair cipher. The following stage is number seven within the context of this competition and it is encrypted according to an adfgvx type cipher. When you attempt to cryptanalyse stage seven you will see that it is more complicated than a straight forward adfgvx cipher. Unfortunately I cannot give you any more clues.

 

In terms of this stage the shibboleth that you should take note of is Molybdenum

You will probably have noticed by now that each stage is in a different cipher and is usually in an appropriate language. So the Vigenère stage was in French and this Playfair stage is in English. If the pattern persists then the next stage will be in German. But does the pattern persist?