In a Kansas library an unknown person has written an encrypted message into a book. Can a reader solve this “book cipher”, which is probably not a book cipher?

Blog reader and Zodiac Killer expert David Oranchak

Source: Schmeh

… has made me aware of an interesting crypto mystery. He saw it on Twitter …

Source: Twitter

… and posted it in the /r/codes group of Reddit. The Tweet was sent by a Kate Ray, who works for the Lawrence Public Library in Lawrence, Kansas. Kate wrote: “Unless you’re the Zodiac Killer, confessing your crimes and revealing your identity, please do not use library books to practice your secret codes.” Kate’s tweet refers to the following cryptogram a reader left behind in one of the library’s books (Assasin’s Apprentice by Robbin Hobb):

Source: Twitter

Dave has published the following transcription on Reddit:


Here’s a frequency analysis made with CrypTool 2:

Source: Schmeh

This frequency distribution is consistent with a letter substitution (MASC) of an English plaintext. The same is true for the Index of Coincidence of the cryptogram, which is 6.3 percent. However, CrypTool 2, as well as online cryptogram solvers, such as Quipqiup or, don’t render a result.

In a later tweet, Kate provided two more parts of the message (the cryptogram is spread to three pages, the second of which contains only one line):

Source: Twitter

Here’s a transcription of the third page (i.e., the second full page) provided by Reddit user Thruster17:


Considering that this message is contained in a book, it seems plausible that a book cipher was used. This would mean that the letters in the cryptogram point to letters, words or phrases in the book. However, I don’t see an obvious way how these letter sequences can be interpreted as page numbers and pointers to certain positions. In addition, the letter frequencies and the Index of Coincidence are typical for a MASC, not for a book cipher.

Can a reader find out more about this strange cryptogram?

Further reading: The Top 50 unsolved encrypted messages: 10. James Hampton’s notebook


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Kommentare (21)

  1. #1 Colin Bierton
    48485 Neuenkirchen
    19. April 2019

    Are there commas, at the end, in the ‘YPMD’ line?

  2. #2 Richard SantaColoma
    19. April 2019

    That looks a lot like a “first letter” mnemonic to me. Perhaps to help remember a speech, or as a crib sheet to recall an essay?

    You may be forever party to your silly yesterdays, seeing no animosity…
    You should never eat mangos that might offend…

    Just kidding, but as an example. It looks like it may be a poem, to me…

  3. #3 Thomas
    19. April 2019

    Most likely a simple substitution + transposition.

  4. #4 Dampier
    19. April 2019

    @Richard SantaColoma

    looks a lot like a “first letter” mnemonic to me

    Same here. The many T’s, I’s and Y’s are striking.

    You may be forever party to your silly yesterdays, seeing no animosity…
    You should never eat mangos that might offend…

    Just kidding

    I also tried to invent some phrases on the fly, and it seemed easy and mostly almost made sense 😉

  5. #5 Breaker
    19. April 2019

    This has a few patterns revealing the methods assigned to each part of the cipher. Using the theme from the “trilogy” there are three breakdowns. The theme is dirty….a spy novel of sorts….

    The “book” is symbolic as it has two pages that are on the front and back. The read on one side may be intended to be seen backwards as well, and there is a mirrored factor in their intended structure as if holding a book in your hands.

    The intention passed is that there is an initial method of the separation of two parts from each page, with 3 similar methods used to crack each page.

    The Theme of the Book?

    An Assassin bringing an Apprentice on a hit.

    Taking note of the initial arrangements, each page of the cipher is then separated into two bodies of text, and then each page is put through its own separations, and three complications applied to produce results.

    1) There is a consistent pattern of lower case and upper case letters so I would separate them accordingly into two blocks of text. After segregating the lower case from upper case, each line is anagrammed to check on that factor. The idea of making a cipher with two sets of ciphertext is so that if they try to use them all together in an anagram maker, the two sets will confuse the read, so this body of ciphertext is then separated into two and put into the word recognition software.

    2) Then count the numbers left in each after separating and arrange them geometrically in a symmetrical grid. Then test letter group combinations for word patterns that were built from this arrangement, according to number counts present…..5,6,7,8 are usually the ones chosen for this type of examination but they may be line for line.

    Noting the patterns of repeating text possibly added as nulls, merely take them one by one and place them in a grid, then count off the pairs, remove them, and then relay the remaining letters out in the next grid. Rotate the grid to the right and reread the text for the next steps, breaking down to a final read after three of these steps. Just a test to see if the “magic squares” will produce anything.

    3) Using the “ABBaa” of the Baconian or Biliteral Cipher Keys you will find another meaning with a segment of the whole body of text that is altered with caps and lower case. ABBaa would be a “N” in Bacon’s alphabet, so this possibly would be a NULL Segment

    Some of these Stennos are even plain as day, and some of the lines have text that are keys to crack the methods down that I mentioned. Seeing that some are fairly easy to see I cite this line as an example:


    A BAD GUY WITH BAG SICK PSYCH CIA TOYS would be the breakdown of the read of this shorthand ‘Stenno’

    The top line of the 2nd page:
    IAAYYAARYNTTMIFLYTIA can be also seen as :

    ****The final step IMO is the use of mistakes and marks of double scored letters as points of reference in a physical map that is made when the page itself is made translucent and overlaid in a certain area on Google Earth. This centerpoint could be Kansas City that is being targeted or it could be anywhere, but there will be some factor found to reveal it all.

    Sorry for being so vague but there is no way to show the results here as its two pages of expanding groupings that are made from 3 different methods used to expand on the basic story.

    Reference the Alster Bottle Mystery Posts for other similar ciphers holding the same themes and using these exact complications.

    The ciphers have been studied more in relation to an ongoing affair here:

  6. #6 David Oranchak
    19. April 2019

    If it’s a first letter mnemonic, then wouldn’t the letters fit the expected frequency distribution in English? Here are the counts:

    T (89), A (88), Y (73), I (63), O (62), S (53), W (52), M (45), N (38), H (32), F (31), D (30), L (28), B (28), C (26), E (17), P (12), G (12), J (10), d (9), , (9), R (7), a (6), K (5), . (5), i (4), t (3), h (3), U (2), y (1), u (1), m (1), g (1)

    Why are there so few Es?

    But it would be interesting to run a large corpus search for first-letter sequences that match.

    Also, Q, V, X, and Z are missing from the cipher alphabet for some reason. Q, X and Z are among the four least used letters in English (X, Q, J and Z); V is only the 6th least frequent letter.

  7. #7 Richard SantaColoma
    19. April 2019

    Hi David!

    “If it’s a first letter mnemonic, then wouldn’t the letters fit the expected frequency distribution in English? Here are the counts:
    T (89), A (88), etc.
    Why are there so few Es?”

    Well I’m far from an expert, but perhaps the frequency distribution of first letters is far different than overall distributions throughout all text. For instance, in the low E count you note, perhaps “E” is simply far less often than the first letter of words, than it appears overall, in words?

  8. #8 Richard SantaColoma
    19. April 2019

    … but nonetheless, your though on this made me wonder if there was a count of frequencies for first letters (that is how much of a noob I am, I didn’t know there was):

    So, assuming for the moment, English, how does the letter count match that first letter frequency list? If it does, it is evidence for a first letter mnemonic.

  9. #9 Breaker
    19. April 2019

    Dave that’s because it is not encrypted that way.

    You can see classic patterns of Biliteral being used in the alternating caps and lower case text, and clear words being shortened with repeating pairs added to confuse word recognition software.

    When there are very few E’s one would expect there would also be a ROT or Caesar Shift that would produce them in abundance from one of the other more popular letters.

  10. #10 Richard SantaColoma
    19. April 2019

    Wow actually… except for “Y”, some seem closer to the frequency counts of first word letters in English… but not all.. here are some striking ones…

    A is 10.11% in the “cipher”, and 11.682% in first word frequency, while only 8.167% in overall…

    E is 2.47% (as you note) in the “cipher”, but also low at only 2.79% in first letter frequency…

  11. #11 David Oranchak
    19. April 2019

    Good points, Richard!

    I did a comparison of the frequencies in a spreadsheet here:

    If we compare the distributions, both via raw sum of differences and via Euclidian distance (between vectors of frequency values), the cipher text more closely resembles the expected frequencies of first letters of words.

  12. #12 Richard SantaColoma
    20. April 2019

    Well that is cool, David! You’ve quantified it perfectly, and I do think it looks like a strong indication this is what is going on here.

    Now it would be interesting to see if their are lists of most common English words starting with each letter… no doubt there are, although I can’t look tonight. But for starters, I think it would be safe to assume some, at least to start plugging them in. “You”, “Your” for Y, for one, unless I’m missing something. “A” would probably be “a” and “and”.. maybe “anything” right behind, or “another”. But I’m getting way ahead of that part of it, without such a list.

    In any case, on the assumption this is a first letter mnemonic, one could plug in the most common words, switch them out for the next, and so on… is it possible? Maybe I can later, or someone can, play with that idea… Wouldn’t it be funny if the seemingly arbitrary guesswork is actually close to a method for solving this?

  13. #13 Richard SantaColoma
    20. April 2019

    Well I did take a minute (OK, more…), after finding this list of the 5,000 most common words:

    Going down the list of the most common words, and filling in for the alphabet with the first 126, I came up with this list:

    a- and, a, at, as, all, about, also, all, any, after,
    b- be, but, by, because, back,
    c- can, come, could, child, call,
    d- do, day, down,
    e- even,
    f- for, from, find,
    g- go, get, give, good,
    h- have, he, his, her, him, how, here,
    i- in, it, i, if, into, its,
    j- just,
    k- know,
    l- like, look, life,
    m- my, make, me, more, man, many,
    n- not, now, new, no,
    o- of, on, or, one, out, other, our, one, over,
    p- people,
    s- say, she, so, some, see, should, still, school
    t- the, to, that, this, they, there, time, think, then, take, than, then, two, these, thing, those, tell, through, their,
    u- up, use, us,
    v- very,
    w- with, we, what, who, will, which, want, way, well, woman, work, world,
    y- you, year, your,

    … for anyone to play with, or me, tomorrow, if I get to it. Considering the odds of this working are probably next to none… slim to none? But might be fun to try this…

    (funny “r” is not in the first 126 words… comes in on the list at #142, for “really”).

  14. #14 Richard SantaColoma
    20. April 2019

    Using the first, most common words for letters that make any sense… moving to the next most common, if it does not, came up with,

    “You may but find people that you say you should not all do, still because you are a child [p] the man”

    So, interesting, but a strike out. Anybody?

  15. #15 Thomas
    20. April 2019

    @David Oranchak
    Awesome! This seems to prove Richard’s first-letter assumption. If only I knew a way of a first letter truncated Google search!

    As to your spreadsheet: Column F seems to contain the letter frequencies of plaintext. But – due to Klaus’s frequency analysis (the index of coincidence of the ciphertext is approx. 0,66) the first letter hypothesis should also be compared to a (simple) substitution (+ transposition overenciphering) hypothesis. Mabe this could be done computing the index of coincidence of the first letter column. (Can’t do it myself with my phone now.) I wonder whether the first letter IoC equals the plaintext IoC in English.

  16. #16 David Oranchak
    20. April 2019

    I kicked off a corpus search which looks for first-letter-of-word matches for all substrings of the library book ciphertext. My corpus is about 450GB compressed so this will probably never finish given my current hardware. 🙂

    Sample hit:

    If I leave it running long enough, maybe it will find a relevant source that matches multiple longer portions of the ciphertext. Generating sequences from lists of common words might work too but I imagine it would be difficult to know which ones were the intended source of the hypothesized mnemonic.

    A better approach would be to generate an index of sequences of first letters of words for the big corpus and put them in an efficiently searchable database of some sort. Someone send me a research grant and a few months of free time to do it. 🙂

  17. #17 Thomas
    20. April 2019

    Calculation done: The index of coincidence based on the first letter frequencies given by Norvig in Wiki (Richard’s link in #8) is approx. 0.065. That means it equals the index of coincidence of a simple substitution (approx. 0.066 in English), hence this parameter can’t help tell one from the other. According to Occam’s razor, I’d prefer Richard’s first letter hypothesis to a (more complicated) substitution-transposition combination.

  18. #18 Richard SantaColoma
    21. April 2019

    Thomas… I suppose I’m unclear on this, so apologies in advance:

    But even though the index of coincidence is similar between the first letter frequencies and simple substitution, as you show… doesn’t the individual, actual, letter frequencies in David’s graph actually still favor first-letter (not substitution) use here?


  19. #19 Richard SantaColoma
    21. April 2019

    Hi David:

    “A better approach would be to generate an index of sequences of first letters of words for the big corpus and put them in an efficiently searchable database of some sort. Someone send me a research grant and a few months of free time to do it.”

    The check is on the way, and thanks. I hope $13.50 will cover it.

    But actually I’ve wondered at this, when looking at the Somerton man’s cipher (which I also wonder if it may be a first-letter mnemonic). Perhaps a useful program would be one that could “strip” the first letter of words in any input text. The results then could be compared easily to suspected first-letter “ciphers”.

    I thought of this with the Rubyat, which I did manually by scanning over the work. It took awhile! I wondered if related works, and other works, could be quickly scanned, stripped, and compared by such a program.

    In the instance in this blog post, suspected works could be used… related maybe to courses offered, poetry held in the library, or maybe texts related to the subject matter the brochure relates to.

    But maybe then it expands into so many possibles that once again we need grants, time, computers running around the clock…

    … all to solve one or two mnemonics which may not be that at all, in the first place. Not really practical, is it, I guess?

  20. #20 Thomas
    21. April 2019

    “doesn’t the individual, actual, letter frequencies in David’s graph actually still favor first-letter (not substitution) use here?”
    Yes, I totally agree. David’s analysis is convincing to me because it takes into account the particular letter frequencies.

  21. #21 David Oranchak
    4. Mai 2019

    An interesting clue was recently found. Whoever wrote the “cipher” in the book apparently circled some letters on other pages:

    The circled sequence is: IAAYYASCNT

    IAAYYA appears in the cipher text.
    Someone near the library is going to try to have a look at the book to find more clues.