In the 1564 printed edition of his cryptography manual, Giovan Battista Bellaso included seven challenge ciphers for his readers to break, along with a set of clues: these all remained unbroken and in obscurity until Augusto Buonafalce wrote about them in 1997, 1999, and 2006 in the journal Cryptologia.

But that’s all changed now!

Tony Gaffney – who Cipher Mysteries regulars should remember from his book “The Agony Column Codes & Ciphers” (under the nom-de-plume ‘Jean Palmer’), his reading of the Dorabella cipher, and his corrections to the Bellaso cipher transcriptions – has managed to crack Bellaso Challenge Cipher #6, despite the handicap of not actually being able to read Italian. 🙂

Here’s the ciphertext in question (with Tony’s starting point highlighted), followed by a description (based closely on the document he posted to the Ancient Cryptography forum) of how he used that to begin solving the entire cryptogram. (Incidentally, if this all comes across a bit like a kind of linguistic Sudoku, it’s because that’s essentially how most non-machine code-breaking is done)…

DP QBGTA ITP LBIEE DFIIHO LI AQILIFF SO NILEECHL OMGTTIE=
CZXRC CGEDFLLIILBGGP PLBBIUNO UL QURNXSRRNB OR ACFEDFLL=
ILBFI PLACFODACU AP UHEEOI PLSGGAOLRIBLNGIBLNPE SO ROCDBCG
BU PCLICB MR RBERPUGSTSLB PLACFOEXBUBLB BPSPDXG QU BDUU
DCCAGE FCFXSFP HP MBHI LH EOMGU FSDDHEIJMG FPDHQMPDD.

Having a repeated block of four letters five letters apart implied that the cipher system involves cycling through five different cipher alphabets: and so Tony trawled through Bellaso’s clues looking “for any word that had a period 5 repetition in it ie. lontano; riteovata; lequale; etc.” When he hit the very promising-looking word consequentemente, he lined that up with the ciphertext letters with the cycle numbers beneath:-

??consequentemente??
PLSGGAOLRIBLNGIBLNPE
12345123451234512345

There’s a problem here, in that in alphabet #4 ‘G’ appears to encipher both ‘o’ and ‘m’: yet because most printed ciphers suffer from typesetter errors, Tony ignored this and marched bravely onwards. 🙂

His next two steps forward were to notice (a) that the second letter in the group shown must be ‘t’ (it occurs in cycle #2 in the same word) and (b) the final letter must be ‘i’ (because ‘e’ is its reciprocal in cycle #5 – Bellaso was fond of reciprocal ciphers, i.e. ones that perform both the ciphering and the deciphering) – so, guessing that the first letter is ‘e’, the above section of ciphertext resolves to ‘et consequentement ?i

Observing that plaintext ‘e’ appears to get enciphered as P in #1; O in #2; N in #3; and I in #5, Tony’s next angle was to rely on the five cycling alphabets’ probably having some kind of symmetry – in particular, because P O N are all a single alphabetical step away from each other, he thought it likely that the bottom half of the alphabet was shifting along by one place in each cycle. This guess let him start to fill out the 5 cycles in more detail:-

????b?e?g??? 1
????nop?????
????b?e?g??? 2
?????nop????
????b?e?g??? 3
??????nop???
????b?e?g??? 4
???????nop??
????b?e?g??? 5
????????nop?

Where next? Well, Tony now turned his gaze on a second repeated feature in the cryptogram, which appeared to be two words formed from the same linguistic root, but with a different prefix and suffix each. Did he now have enough letters to solve this? He decided to give it a go regardless:-

ACFEDFLLILBFI &
 CGEDFLLIILBGGP
??o???????????   ???o???t?????
CGEDFLLIILBGGP & ACFEDFLLILBFI
51234512345123   5123451234512
??o???t???n???   s?????tq??n??
CGEDFLLIILBGGP & ACFEDFLLILBFI
12345123451234   1234512345123
?????tq?????o?   ?s????q??????
CGEDFLLIILBGGP & ACFEDFLLILBFI
23451234512345   2345123451234
so???q???t?one   ???p?????t???
CGEDFLLIILBGGP & ACFEDFLLILBFI
34512345123451   3451234512345
?np??????q????   ???o?????q???
CGEDFLLIILBGGP & ACFEDFLLILBFI
45123451234512   4512345123451

Looking at the fourth set, he wondered if ‘t?one‘ might well be ‘tione‘, and so tried them both “as if they were the same word”. Removing the extra I from the first word yields:-

?np?????tione   ???p?????ti??
CGEDFLLILBGGP & ACFEDFLLILBFI
4512345123451   3451234512345

His original table for #3 maps ‘e?g‘ to ‘nop‘ so it seemed entirely possible that ‘F’ might encipher ‘o’: and so guessed that this word was something along the lines of the word ‘proportion‘:-

?n proportione   ??? proporti??
CG EDFLLILBGGP & ACF EDFLLILBFI
45 12345123451   345 1234512345

Working with the code-breakers’ two secret weapons (controlled mistakenness, allied with bloodyminded persistence), Tony moved forwards, safe in the knowledge that if his guesses were significantly wrong his errors would soon present themselves. How much of the five alphabets did he now have?

??r?b?efgl?? #1
??i?nopqt???
??r?b?efgl?? #2
??di?nopqt??
??r?b?efgl?? #3
????i?nopqt?
??r?b?efgl?? #4
??u??i?nopqt
??r?b?efgl?? #5
??t???i?nopq

He now moved on to the next weakest link in the ciphertext, a long group of letters (‘RBERPUGSTSLB‘) that he thought might well now be solvable with the letters he had:-

i?nu??qc????  di??e?p??ati  ??iif?o?g?q?  u?pdgrnalcp?  ?no?l?t???on
RBERPUGSTSLB  RBERPUGSTSLB  RBERPUGSTSLB  RBERPUGSTSLB  RBERPUGSTSLB
123451234512  234512345123  345123451234  451234512345  512345123451

Pleasingly, ‘distemperati‘ seemed to fit the second version (‘di??e?p??ati’): and so he proceeded with all the remaining words in the challenge cipher.

Tony’s final plaintext (parallel with the ciphertext, and the matching cycle numbers) looks like:-

della giors cre ticip rocede qualche ilcorpo nostro ecoposto
DP    QBGTA ITP LBIEE DFIIHO LI      AQILIFF SO     NILEECHL
      23451 451 23451 234512         2345123        34512345
etorganizato inpropor tione musicabe poi maicretici sono
OMGTTIECZXRC CGEDFLLIILBGGP PLBBIUNO UL  QURNXSRRNB OR
23451234-451 45123451*23451 51234512     4512345123
disproportine etdiscrdia nella musica etconsequenteoenteli nostro
ACFEDFLLILBFI PLACFODACU AP    UHEEOI PLSGGAOLRIBLNGIBLNPE SO
3451234512345 1234512345       234512 12345123451234512345
uloriin quella giorni sono distemperati etdiscordanti ilferro inogni
ROCDBCG BU     PCLICB MR   RBERPUGSTSLB PLACFOEXBUBLB BPSPDXG QU
4512345        345123      234512345123 1234512345123 3451234
sara condoi soprese della vite per petoa saratirato serumpera
BDUU DCCAGE FCFXSFP HP    MBHI LH  EOMGU FSDDHEIJMG FPDHQMPDD.
2345 512345 5123451       2345     12345 5123451234 512345123

Bellaso appears (as per his book) to be using two letter groups to stand in for common words:

  • DP — della
  • LI — mille/qualche
  • SO — no macati e sequir/quanto/ve habiamo/scritto/nostro
  • UL — vostra/poi
  • OR — perilche/sono
  • AP — della/nella
  • BU — ditto/quella
  • MR — il vostro/sono
  • QU — quella/inogni
  • HP — della/imperoche
  • LH — intutto/per

Finally, Tony notes – “I am greatly indebted to Augusto Buonafalce for his help in translating some of the words and supplying me with copies of his English translations of the books.

The plaintext refers to Bellaso’s clue #8, and discusses the well being of the body at different times, which could well refer to the theories of the Renaissance astrologer Andrea Argoli.

All I can really say is that I think this is a splendid achievement, and I wish Tony the very best of luck with the other challenge ciphers! Excellent, well done! 🙂

3 thoughts on “450-year-old challenge cipher cracked!

  1. Dennis on April 2, 2009 at 5:46 am said:

    Bravo! A splendid example of hand cryptanalysis at its best. Please extend my congratulations to Tony!

  2. Krqleuswztlokwmhmlnhjtndwi 55 33 999 7 2 3

    We are geocachers and need to crack this Bellaso code to gain a hint to coordinates, 5 of us are looking and can find nothing as an easy type code breaker, any ideas or would this one be a simple one you can answer for us, please thanks.

  3. Pingback: Una solución a medida para el Documento Sirtori | Ideas Excel

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