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# Five encrypted thoughts

## Question

This 324-character message is an encrypted quotation:

```XPRXWUIWUOLZYXBFTTJMDVOCTTXPPPKLEVROQPRFPLTHWSMOGVCYPG
LHKHKLSJSLGKZYFYBUTFTOSFHHMZGRQFELYEKFHWILBDBDROHIZLIM
MILZIHORDBDBLIWHFKEYLEFQRGZMHHFSOTFTUBYFYZKGLSJSLKHKHL
LHNZTBTPXFWOIHZVAOXVNJRMYUBGMOAAOMUYXHMARGFWPYGEIHJISQ
GPYCVGOMSWHTLPFRPQORVELKPPPXTTCOVDMJTTFBXYZLOUWIUWXRPX[/code]

which was encrypted in the following simple way:

1. The quotation has been converted to numbers using A=0, B=1, C=2, ..., Z=25.

2. A second stream of numbers is made by reversing the sequence of numbers made in 1 above.

3. These two streams are added modulo 26.

4. The stream produced in 3 above is then converted using 0=A, 1=B, 2=C, ..., 25=Z.

The result of all this is the 324-long stream above.

Here is an example of encrypting a different quotation:

[code]ITHASYETTOBEPROVENTHATINTELLIGENCEHASANYSURVIVALVALUE```
```  I  T  H  A  S  Y  E  T  T  O  B  E  P  R  O  V  E  N  T  H  A  T  I  N  T  E  L  L  I  G  E  N  C  E  H  A  S  A  N  Y  S  U  R  V  I  V  A  L  V  A  L  U  E
8 19  7  0 18 24  4 19 19 14  1  4 15 17 14 21  4 13 19  7  0 19  8 13 19  4 11 11  8  6  4 13  2  4  7  0 18  0 13 24 18 20 17 21  8 21  0 11 21  0 11 20  4
4 20 11  0 21 11  0 21  8 21 17 20 18 24 13  0 18  0  7  4  2 13  4  6  8 11 11  4 19 13  8 19  0  7 19 13  4 21 14 17 15  4  1 14 19 19  4 24 18  0  7 19  8
12 13 18  0 13  9  4 14  1  9 18 24  7 15  1 21 22 13  0 11  2  6 12 19  1 15 22 15  1 19 12  6  2 11  0 13 22 21  1 15  7 24 18  9  1 14  4  9 13  0 18 13 12
M  N  S  A  N  J  E  O  B  J  S  Y  H  P  B  V  W  N  A  L  C  G  M  T  B  P  W  P  B  T  M  G  C  L  A  N  W  V  B  P  H  Y  S  J  B  O  E  J  N  A  S  N  M[/code]
The result of this is the 53-long stream:
MNSANJEOBJSYHPBVWNALCGMTBPWPBTMGCLANWVBPHYSJBOEJNASNM

What is the quotation which has been encrypted to the stream above starting XPRXWUIWUOLZYXBFTTJMDVOCTTX... ?```
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## 18 answers to this question

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Very interesting! This is going to be loads of fun, woohoo.

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This one is hard. I do not suppose we can get a hint like what letter 162 should be?

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B

I have hints in the form of words which appear in the text. I'll post them (one at a time, of course) if you want them.

Edited by superprismatic
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I am starting in the middle and working out, so words would not help me any, unless I knew where they went maybe. That letter is helpful, I had skipped past it.

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Good. If you need any small hints, I'm willing to dribble some out now and then. Just ask.

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Okay, letter by letter is getting me nowhere fast. I think that a brute force with a dictionary could probably break this pretty quickly though, but I do not have access to that other than manually, which would be pretty slow. I can find a word if it is in there somewhere, so I will ask for a word hint please.

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Interesting, but I am sceptical about whether word hints will help solve subsequent parts of the message unless there are a lot of words given. I'm going for bruteforce.

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It is easy to encrypt as specified with the aid of a spreadsheet but the encryption will always be a symmetrical string. Given either first half or last half of solution, it would be easy to determine the other half with a spreadsheet. The problem arises that every letter in the encrypted can be any one of at least 13 different combinations. If you do not know one, you cannot positively identify the other. Bottom line, this cannot be decoded by any algorithm. With sufficient hints and basic word composition rules, we could eventually get the answer but it would be an elaborate maze of guesses, especially since no spaces are provided for word division.

Edited by thoughtfulfellow
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Okay, letter by letter is getting me nowhere fast. I think that a brute force with a dictionary could probably break this pretty quickly though, but I do not have access to that other than manually, which would be pretty slow. I can find a word if it is in there somewhere, so I will ask for a word hint please.

THOUGHT is in the message 5 times.

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It is easy to encrypt as specified with the aid of a spreadsheet but the encryption will always be a symmetrical string. Given either first half or last half of solution, it would be easy to determine the other half with a spreadsheet. The problem arises that every letter in the encrypted can be any one of at least 13 different combinations. If you do not know one, you cannot positively identify the other. Bottom line, this cannot be decoded by any algorithm. With sufficient hints and basic word composition rules, we could eventually get the answer but it would be an elaborate maze of guesses, especially since no spaces are provided for word division.

Okay, letter by letter is getting me nowhere fast. I think that a brute force with a dictionary could probably break this pretty quickly though, but I do not have access to that other than manually, which would be pretty slow. I can find a word if it is in there somewhere, so I will ask for a word hint please.

Each character can be decoded into one of 26. Even using a dictionary, the biggest problem is not speed (though it is a major issue anyway), but how to recognise words. The most commonly used dictionary has 250000 words, which is too many. If a search algorithm accepts words of any length, then the search would start off creating many trivial words like BA or CA, words that are virtually never used; there is no easy way to distinguish MEANINGFUL words. This might be faintly plausible if I could find a dictionary of common words only.

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The five words corresponding to THOUGHT:

81:87 SHORTY

110:114 NEAR

250:253 SORE

211:215 REAR

228:232 HUNT

Is there slang in this?

If I had nothing else to go on, I would start looking for "near the", "is sore", "hunt the", "a thought", "thought of" "i thought", etc.

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Since I googled to get the answer, I am not sure if I should post it in case others still get it without google, but I will just give the initials of the one who is quoted, B R. (their full name is in the quote, not their initials).

I already have it solved, though I used the word hint to get enough words going the other way to let me use google to get the full quote. That might be kind of cheating the point of a decrypt though, so I have not posted anything.

Voider, I think your algorithm may have an error. Those words are not the ones I have going the other way if the word thought is put at those positions. Assuming the first letter is letter 1, if thought is entered at 81-87, the corresponding section in the other half is

Q K G E G U N

although if you entered "thought" at position 79, I see you would get "trohsfv" going the other way, but the word "short" is in there backwards and has the unlikely combo "fv" after it. I checked your other locations and the words are all backwards. Entering thought at letter 81 should give you qkgegun for the other side, and entering thought at 79 should give trohsfv. What I have is correct since I did enter the actual quote in the first half and checked the 2nd half to verify it all worked and to have a copy of the quote as encrypted in case there were any changes made to the one I found on google.

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Please tell me if I am on the right track

THOUGHT starting at positions 6, 113, 129, 178 AND 231. And TABLE beginning at position 190.

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129 is correct, and so you know 190 is correct also. The others are not correct.

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Men fear thought as they fear nothing else on earth more than ruin more even than death. Thought is subversive and revolutionary, destructive and terrible, thought is merciless to privilege, established institutions, and comfortable habit. Thought looks into the pit of hell and is not afraid. Thought is great and swift and free, the light of the world, and the chief glory of man.

~Bertrand Russell~

I hope that's it because I've tried to solve this one for a looooooong time.

if not, hey i tried. I like the quote though.

Edited by plainglazed
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I just wanted to say to all you puzzle solvers on this post that I am sincerely sorry if I ruined the fun for blurting out what I thought was the answer. I was so thrilled to think I had solved it, that I didn't think about that possibility. I tried to erase it, but it will no longer let me edit that post. Again, very sorry if that was the answer, but crack on fellow puzzlers! My hat off to you!

EDIT: no worries, thanks for your concern - added the spoiler tags above - welcome to the Den Chronic. - plainglazed

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Men fear thought as they fear nothing else on earth more than ruin more even than death. Thought is subversive and revolutionary, destructive and terrible, thought is merciless to privilege, established institutions, and comfortable habit. Thought looks into the pit of hell and is not afraid. Thought is great and swift and free, the light of the world, and the chief glory of man.

~Bertrand Russell~

I hope that's it because I've tried to solve this one for a looooooong time.

if not, hey i tried. I like the quote though.

Indeed, you've got it. Nice going!

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Many thanks for the "spoiler tags"...I'm still trying to figure this place out. Funny I can solve a puzzle but not how to work a web site! And I can't tell you how ecstatic I am that I actually had the correct answer! When it first came out I worked on it for such a long time that I finally had to stop because my eyes were twitching from the strain. Superb puzzle and I can't wait to find another like it!

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