First up: I am not asking you to decypher anything. This question is about attacking a Playfair cipher; more specifically – how to create potential grids when doing so.
I'm currently working on a message in playfair cipher text. The issue is there is no grid, and only potential crib is attack. I was told there is a key used, but we have to discover it.
What I‘ve tried (and been able to do)
After using frequency analysis, I managed to find that
QK appears to be the letters
th since it is the most common diagraph. I found that
V are most common letters in the ciphertext after the letters
iagraphs that follow QK VE - CQ - AH - RQ - VM - BC - BP - VU - SG - SH - CF - UV - UY - SZ - SQ - VQ - FH - AE - RZ QK - VE = 1 QK - CQ = 4 QK - AH = 1 QK - RQ = 2 QK - VM = 1 QK - BC = 1 QK - BP = 2 QK - VU = 1 QK - SG = 1 QK - SH = 2 QK - CF = 1 QK - UV = 1 QK - UY = 1 QK - SZ = 1 QK - SQ = 1 QK - VQ = 1 QK - FH = 1 QK - AE = 1 QK - RZ = 1 Most common after QK: CQ ciphertext: QKVEPTQDEURAQKCQFCQGNWKWQARIVTVQQADVGHQKCQQHFMUQUHGBNWPMPFQKAHMSDHPRRB ZRSMYKVXVRVUQWPZPFBPFHDZZUUWUVLWSPKQPMHVKMVTBPACWYQKRQMVWLQKVMSFNQQANW KDMKMVRADPGEEVVYQHYVKZYMGBUEYVDQTIPLVUVYPZRPOYWKRASHUVUYEVLDSEOKMKHDUM SUIZSEXKMVQKBCHUXQMVTKOYISCMKXQKBPHCPXIMGWVRVUQADECMGBYOESUVGEQANWNKCF KXFHFLMTOYSGSNQKVURQOYKNOPSHAHDWQHUMMVKBKBYKAHDWQKCQQDEGESSLSMEVCQQCKT QKSGQDRIMVRHOPRHOYWKUZSPKZULQLVURQRQRHHDWKAHVYQKSHVZHNSZKFQHSDVQQATPHU XYQLCQQDESKIVWQAIGKZRNALCEVQQAKIBPYOGSWXGEKBQCESSLSMEVQKRQDEMVRZVUASKF TIDMQHQVRVSWBVQDKXOVDCNWPMYOWXGEDHUVCFTIPBQKCFZUUHQLCQQKUVRZBKQKUYGSKF UQVRVUTIHUBSILRABKQKSHFHOGWVGZPXBVUVZRBIVUQLCQOYQDRPOPSHVZHNSZSEXCUVCH BPCIVXIMDEGMPFSNQKSZELBVEVUYVYAHPMPFCBMCFSPUEPBTVOBPASRVSWQKBPCYQHWOVC RAOPKBXWQKSQLSMIFZPWPONWHRLRMVSHVZHNVQQAEDBIIVFHCWQAUSHFQDXGMSVEFHCWQA WVCGGBDCFTGOARKXEGLFBSVYQKVQQAQLMKAQSFRZVEVYQHWXUHMTDCNWKWQADSAHYKFHOG QKCQVYFNCNMPHRLRMVSHVZHNAHXCMSVYQKFHQKAEMBIZVEGMGMLPRQTIPLVURYGEESNYKI EVCWMIVQQAFCQXVUVEOVUVFDBKGBARKFVQVOQADZVUOGFHHSIKHRBPVYAHLMSHEDKOOGDH PWOVWLQKRZOVPOUYVYQAMSUFWYYVCIMCIXSZGBWXGEKXCBVWQAVIVXQHDUOGFHHNFHZPCE UHMCBVOXQRTMRNFCNWNMVEKMVFPZPFFHLRZCPBPFSMAPXKMTZDBUVMVTRYMVWLQDEM
I'm pretty sure
er/re. But I am asking myself if one of these could be
I am having trouble figuring out how to get the right idea to help create a potential grid that would lead to the deciphering the text. How can/should I create and validate potential grids when attacking a Playfair cipher, based on what I’ve got so far?
(In case of doubt: I am looking for a “how to”. This is not a “decypher this” question.)