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## Heroes of BP 1

A cache by mjcross Message this owner
Hidden : 04/22/2018
Difficulty:
Terrain:

Size:  (micro)

#### Watch

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### Geocache Description:

There is nothing hidden at the listed coordinates: solve the puzzle to get the location of the cache.

The dedication, innovation and brilliance of the men and women who worked at Bletchley Park and its equivalents elsewhere defy comparison. This series of cryptographic puzzles exists to celebrate their achievements, and to challenge those capable of visiting their arcane world.

 Please be aware that these are rather specialised and extremely difficult puzzles. I set out to create something worthy of the B.P. cryptographers themselves, and that inevitably puts the series beyond the reach of many people. The messages are all in English and you won’t need to be a mathematician to solve the puzzles (I’m not) but you must be able to think like one - and to be prepared to research, learn and experiment. Be aware that each puzzle took me several weeks of research and investigation to construct and validate; so solving them will be a lengthy process. But I promise that they are all entirely doable.

 I appreciate that whilst Joan and her colleagues were quite accustomed to solving quite complex problems within nothing more than a sharp pencil, a pad of squared paper and a really strong cup of tea, latter-day solvers may have grown a little soft. Consequently I am making available here a few modular matrix algebra tools that might come in handy; and a here a short primer on LFSRs. Solvers new to the topic might also find the following website useful to understand what the hint is talking about.

Rain on the windows. 2am. Somewhere a fox was calling. Reluctantly she accepted that sleep was not going to return... might as well get up and head back in.

An hour later she was showing her pass at the main gate and heading to the top of the site, picking her way around the puddles. Then almost as if she’d never left, she was back in the familiar dimly lit main corridor of Block F and turning left into the spur marked Research.

Nodding at a colleague (this place never slept) she hung up her coat and got herself a cup of tea. Heading into registry to collect her in-tray, the clerk looked up. “Oh - Joan, hello... got a new one for you - you’ll need to sign for it though.”

The big manilla envelope was secured with tape and signed across the seal. She held it awkwardly under one arm while balancing the tea and unlocking the office door. The file inside carried the diagonal red band that signified specially sensitive information.

The cup of tea, untouched, had long since gone cold. Outside the birds were starting to sing. She reflected on what she’d read so far. A new type of encrypted enemy comms. No decodes yet, but the schedule and message lengths suggested signals to clandestine agents.

The final sheet was a handwritten note in the unmistakable blue pencil of Ralph Tester: “Vernam cypher? - some whispers about a new binary key generator using a 61 bit linear feedback shift register. Tell me if you get anywhere.”

It wasn’t much to go on. An LFSR would be much easier to attack than some things, but she was going to need a sample of key.

The file had a couple of intercepts - successive messages on the same day; the second at precisely 13:00. No preamble, so they probably just initialised the crypto at the beginning of the day and let it run through without re-keying between messages. Groups of five bits... almost certainly a teleprinter then. Beyond that, anybody’s guess.

 TX BEGINS 11:43:20Z 00010 11001 00110 01010 11000 11000 10000 00101 00111 10111 00010 11101 11010 10000 01010 10001 10010 01010 10001 10000 10100 11010 01011 11110 11011 10001 11110 00110 01110 10011 11100 11010 11101 10111 00100 00100 01010 10100 00011 10100 01111 01000 01000 00000 10001 10110 00010 10010 01000 01000 00111 01011 00010 00000 01011 11000 00110 01010 10110 00100 01110 00100 11111 01011 10010 01101 01000 11010 01101 00110 11000 10011 10100 01111 10010 11011 10011 00010 01011 10010 11111 10111 00100 00110 10001 10110 10101 01101 01100 11011 10110 01010 01110 00010 01110 01001 10010 10101 01111 10111 00111 00000 10001 01011 11101 00101 10000 01001 11001 10011 11100 TX ENDS 11:43:31Z

 TX BEGINS 13:00:00Z 10000 11010 10010 10011 10010 00010 01111 00010 10010 11000 10100 01100 00101 00000 01010 11111 11001 10010 11001 11010 01000 11001 01001 10101 11101 01101 00011 01100 11010 11010 01010 00100 11000 01001 11101 01101 00110 11111 11010 01111 11101 00110 10110 01100 01101 11000 01101 11010 00000 10101 11011 00100 00001 10100 11111 11001 11110 11101 00011 00000 10111 10011 01001 11101 00001 10011 00001 00110 10010 11110 00101 00111 10000 01100 11011 10001 00001 01100 10000 11001 10110 00010 01101 00010 TX ENDS 13:00:11Z

At lunchtime it was raining even harder. She must remember to switch on the wireless to catch the one o’clock weather report. Suddenly it struck her. Lunch forgotten in an instant, she turned on her heel and sped back to the block - calling to the suprised registry clerk “Sally! Send across for a weather forecast crib will you? And dig out Major Tester…”

 M O S T   S E C R E T Weather Forecast Crib Sent as : binary, 5 bit groups Encoding: ITA2, LSB first Crib len: 125 bits Crib start pos: bit 0 Crib [Letters]WEATHER[Space]FORECAST[Space][Figures]HH:MM[Space] 11111 11001 10000 11000 00001 00101 10000 01010 00100 10110 00011 01010 10000 01110 11000 10100 00001 00100 11011 ..H.. ..H.. 01110 ..M.. ..M.. 00100

Congratulations to CASH and Gary for the FTF

Oreyrxnzc-Znffrl

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)