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## Crouching Panda, Hidden Venona

A cache by Team Mumu Message this owner
Hidden : 11/01/2008
Difficulty:
Terrain:

Size:  (small)

#### Watch

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### Geocache Description:

This is a puzzle cache. The given coordinates are for the parking area. Solve the puzzle, then take a short hike and go find the cache.

## The Puzzle:

We have been tracking a gang of thieves, code named Big Fish. Intercepted messages strongly suggest that a cache of valuable items has been hidden in deep cover in the woods of Westchester County.

As described below, the Big Fish Gang communicates the coordinates of secret locations using a code book and a one-time pad. Although one-time pad ciphers are normally unbreakable, in this case the same one-time pad was used to send two messages, giving us an opportunity to crack the code. In addition, we have recovered a copy of the Big Fish code book. Your job is to crack the code and find the treasure.

Here is the first cipher text:

67009 48105 64953 07924 08589 35281 46882 61109 02346 65584

Here is the second cipher text:

05590 79658 93473 93753 25647 53170 06502 75509 30954 93151

Here is the code book:

 UTM 20778 WGS84 68269 degrees 11110 east 58357 easting 47456 eight 08452 eighteen 56803 eighty 56546 eleven 85037 fifteen 09196 fifty 61748 five 39526 forty 85323 four 21313 fourteen 66797

 hundred 69032 latitude 26374 longitude 70801 million 40076 minutes 46054 nine 55090 nineteen 41126 ninety 94111 north 75158 northing 20844 one 33285 point 54772 seconds 04718 seven 07846 seventeen 51482

 six 94052 sixteen 26383 sixty 12544 south 43346 ten 60800 thirteen 42177 thirty 56217 thousand 10930 three 66485 twelve 97308 twenty 11425 two 36060 west 98859 zero 42911 zone 44605

The decrypted coordinates will lead you to a decon container hidden under sticks within a multi-trunked tree. Total walk is less than a mile round-trip through a pleasant nature preserve with a few stream crossings. We encourage you to stay on the trails until very close to ground zero.

## Background:

The Venona code is a double-encrypted system in which words are first converted into numbers by using a code book and then the numbers are scrambled using a one-time pad. Code systems that use a one-time pad are theoretically unbreakable if they are used correctly.

The first step in the Venona code is to look up the words of the message in a code book that maps words to numbers. For example, if the code book contains:

 agency 91348 anything 63165 never 51076 no 11641 say 61089 such 14902

then the phrase "no such agency" would be converted to:

  no   such  agency11641 14902  91348


The second step is to apply the one-time pad. The one-time pad should be a completely random and unpredictable string of bits. Suppose the one-time pad contains the following "random" blocks:

61723 61135 45799

To complete the Venona encryption, write the encoded number above the one-time pad and add the digits one by one, without carrying. Thus, the final output would be:

encoded message   11641 14902 91348one-time pad      61723 61135 45799                  -----------------final cipher text 72364 75037 36037


To decrypt the message, the recipient must also have the same one-time pad. Simply write the cipher text above the one-time pad and subtract, again without carrying:

final cipher text 72364 75037 36037one-time pad      61723 61135 45799                  -----------------coded message     11641 14902 91348


The coded message blocks are looked up in the code book and the original message is reconstructed.

Crypto systems that employ one-time pads are theoretically unbreakable if they are used properly. But if the one-time pad is re-used, and the code breaker has access to two cipher texts created with the same one-time pad, then he or she can exploit the difference between those two cipher texts to reconstruct the original messages (plain texts).

[puzzle] Ernq nobhg ubj gur erny-yvsr Iraban pbqr jnf oebxra ol gur cerqrprffbe bs gur AFN.

[cache] zhygv-gehax gerr

Decryption Key

A|B|C|D|E|F|G|H|I|J|K|L|M
-------------------------
N|O|P|Q|R|S|T|U|V|W|X|Y|Z

(letter above equals below, and vice versa)

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