Grandpre con

I updated the interactive Grandpre solver on Bionsgadgets so it now has undo-redo buttons. Here’s a randomly generated Grandpre that I tested it on.
My “sloppy” grandpre hill-climber using the crib solved it quickly.

Grandpre:
16 52 32 33 68 15 57 58 33 65 88 74 75 43 41 55 52 82 73 24 17 11
52 62 22 85 52 37 25 87 44 85 57 63 41 75 62 28 73 64 62 25 44 32
87 22 74 37 61 41 75 87 46 84 16 53 27 52 72 72 36 73 82 57 25 61
12 78 51 84 88 74 37 62 84 51 15 77 57 76 52 41 37 33 15 81 72 25
15 52 75 73 58 62 42 57 31 55 66 12 33 42 68 51 46 41 75 72 25 55
74 55 57 58 82 75 16 13 75 65 74 32 76 28 75 52 15 62 23 46 11 28
57 66 36 42 73 36 57 42 52 73 35 57 43 64 57 82 26 74 75 52 75 87
31 41 33 41 57 81 61 53 63 35 37 13 51 48 36 24 25 36 37 81 87 58

crib: toleavewiththe

5 thoughts on “Grandpre con”

  1. Thanks – I tried it out and it worked fine, but I recognized the quote before I needed to undo anything. The “sloppy” solver sounds like a win!

  2. Looking through the code for the sloppy Grandpre solver, it has two unusual features. It ignores vertical key words and it scores trial decrypts using logs of pentagraph frequencies instead of logs of tetragraph frequencies.

    The solver is written in javascript and it uses “web workers” which run in the background. I run it from my local storage, but I can’t run it as a local file because Chrome won’t let background processes run from a local file. Instead I have to start up a local web server and run it using the address “http://localhost:8080”.

  3. Do log pentagraphs work better than log tetragraphs for everything, or just for this? I’ve avoided them in the past because I didn’t have enough reference text for adequate coverage at the time, but there’s a lot more available now. I mostly focus on log tetragraphs in hopes of getting close, but reward words when they appear.

    The requirement for a local web server seems like a nuisance. Chrome seems to want everything to be in the cloud, but you’re like Joe Btfsplk in Li’l Abner, with a small local cloud following you around.

    1. The only cipher types in which I know that log pentagraphs work better than log tetragraphs are ciphers where any plaintext letter has many possible ciphertext substitutes (ciphers with homophones in other words), there is no crib, and in addition there are few or no restrictions on the key. For example Numbered key ciphers and ciphers with homemade symbols (such as Zodiac’s first cipher). In cases like that hill-climbing often turns up gibberish decrypts whose log tetragraph score is actually higher then the log tetragraph score of the solution.

      The sloppy Grandpre hill-climber was just an added option to my regular numbered key PH hill-climber which already uses a combination of log pentragraph and word list scoring. The log pentagraph frequency table was already built in so I decided to use it. Whether it really needs log pentagraph scoring to be effective I don’t know.

      The reason Chrome gives for needing a local server to run web workers from the local disk is ‘security’. Whether or not this is true I don’t know.

      Rereading this post I see that my ignorance of many computer topics is still vast.

  4. I found a file called “notes_tet_vs_pent.txt” and it contains a numbered key cipher that was solved without a crib by log pentagraph scoring plus a huge word and phrase list. The solution took over 42 million trial decryts.

    But using log tetragraph scoring even with word lists there was a gibberish decrypt with a higher score than the score of the solution.

    The length of the extended key is 42 and the plaintext length is 83 so it’s beyond the ACA guidelines. Here it is:

    Numbered key:
    00 05 28 10 01 28 22 21 34 28 10 10 01 33 10 00 25 29 31 40 35 00
    17 33 35 33 38 33 31 21 06 31 40 05 28 19 23 21 15 32 10 10 03 23
    25 40 15 00 13 19 31 35 00 05 40 08 25 29 06 00 13 00 02 11 30 15
    37 08 00 25 16 25 10 01 19 34 21 02 36 31 40 10 10.

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