# Stuff to do while you wait (with a message from Harry added)

The Empty Vault Forums Bureau of Security and Signals Intelligence Forum Stuff to do while you wait (with a message from Harry added)

• This topic has 58 replies, 12 voices, and was last updated 2 months ago by The-Letter-Wriggler.
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• #84946
Participant

[As usual, Madness is providing the more advanced cipher crackers with some fun here, so don’t be too put off if you don’t know (yet) what he is taking about! Once you have been here long enough you will be tackling these challenges with ease. Harry

ps, the MD5 lines are what are known as hashes of the original plaintext and the key that madness has used. If you can break the ciphers you can use an online tool to make an MD5 hash of your solution and of your keyword and compare them with madness’s md5s to see if you were right.]

The Mirror Vigenere Cipher

This challenge is so easy, I was debating with myself whether to
even post it. But what the heck.

You know how the Vigenere cipher can be defined by how it acts on
each plaintext character? If we think of the letters A…Z as numbers
0…25, then for a key with period m the ith ciphertext character is

c[i] = (+p[i] + k[i mod m]) mod 26

For the Beaufort it is

c[i] = (-p[i] + k[i mod m]) mod 26

and for the variant Beaufort

c[i] = (+p[i] – k[i mod m]) mod 26

So we have:

sign of p | sign of k | cipher
+ | + | Vigenere
+ | – | variant Beaufort
– | + | Beaufort

Try to imagine that the above table was formatted nicely.
Obviously, one combination is missing, namely – -.
Introducing the Mirror Vigenere Cipher:

c[i] = (-p[i] – k[i mod m]) mod 26

It is so named for reasons that I think are obvious.

Here are two ciphertexts, one long and easy, and one short and less easy.
Your task is to break them and recover the keys. Try to have fun.

DERWNPSZQPTTKWYFHWKSCSWCYISCNAPJWORGNCHZWWVDGOFNYLWQNDPJIOEJCPOAGDQGBOFJULXICIPFGIFW
KOEGBUJQVTEJFDQKNVOUBAXXNEIBPUQRSMJZNAQGNPSWQPTMLSWIBFTCTDPJNOKRCFYZPJTPCFUNWDTZVYIT
ZJJOMJLJREJQPROWFELWWSENWTEDCJEBVMTISKSVPHPXNPWUSIJYNIIMPDEDGDKNLVTWTLYYSSEGTUSEPEER
SKWDFOEZSIMNROSRZSYGJTXFYFSRFLMRZSJUCSWWSMENSSFWUSDGBJRZYMSZPFWWSMEZWLZRZSAZSTFESDPJ
NFJXAAWPBMKWKDPNQVTIGCEJBBTDCLTTUIKGSRITSVJWWEDZQPTEVWEVJJURZSJUCSZDSLTTUIKGYJDGFIED
CFFZVK

MD5 of keyword: f2af9578745b09c5b22a3575e7a2f5fc

SCSLIHIOHKMDOLDAEKWSEPAFPJBYSPHIOSLAXAYJXISVNGDDUTPHMRDPRPKANHFFIHIONIMFKLQUESGEJBEM

MD5 of keyword: b6b818304a439f91fc90b3fe8dd35be8

#84494
person_314
Participant

[This has been in the inbox for a while, but I figure that those who are still taking part might enjoy it. Harry]

For those of you (like myself) stuck with problems 2 through 5 and for those who are newer to all of this here is an easier cipher inspired by current events.

Royal Cipher:

IRIIIIIIIICCRCCIRIIICCCIICCIIICIIICIICCRIICCIIIICIIIIRRCCIIIRCIIICIIICCCIIICCIIIIIIIIIICRICIIIIRCIIIIIICCIIICCIRIIIIIIIICRCRRIIICCIIIIRIIIIIIIIRRIIICCICCRCCCCIIIIIIRIIIIIIIICRCRIIIIIRRRRIIIIRCIIIIIIIIIIICIIIIIIIICRIIIIIIICCIICRCIIIIIIICIIIIIIIICIIRIIIIRCIRIIIIIICCCICRCIIIIIICCIIIIIIRRIRIIIIIIIICRIIIIRCCCCCRIIRCIIICIIICIICCRRCRCIIIIIIIRCCIIICIIIIIRIIIIRCIIIIIIIIRIIIICCIIIRCIIICCCRIIIIIIIICIIIICCCCRIICCCCCRCICCIIIIIIIIIIIRIRRIIICIIIRICIIIIIRIIIIIIIIRRIIIICIIIIIRIIIIRCCIIICIICCRIIIRIIIIRCCIIICIICCRIRCCIRCCIICCIIIIIRCCIIICIIIIIIIICCIIICCIRIIIICCIIICCIIICIIICIRIIIIIIIICRIIIIRCCCIIIIICRIIIIIIIRIIIIIIIICRIIRRCRIIIIRCIIIICIIICRCIICIIICIIRCCRIIIIIIIIIRIIIIIIIRCCCIIIIIIIIIRRRIIICIIIIICIIIIIRIIIIIICCCRIRCIIIIIIICIIIRRIIICRCIIIIIIIIRIIIIIIIIIIIIRIIIICCIIICCCRIIIIIIIIIIRRIIIICIIIIICIIRIIIIIRIIIIICRCRIIIICCRIIIRIIICCCRRCCIIIIIIIIIRIIIIRCCIIICIICCRIICCIRIIIICCIIIIICCCRCCCIIIIIIRCCCIIIIIIRIIIIIIIICIRCIIIIIIIIIIIRIIIIIIIRCRIIIIIICRIIIIIIIRCRCRIIIIIIIIRIIIIIIIICRICCRCICCIIIIIIIIIIIRIIRIIIIIIIICIIIRIIRRCIIICIIIIICICRIIRCCIIICIIIIICIIRIIIIIRIIIIICIICIIIIRCIIIIIICCIIICCIIIICCCCIIIIIIIIIRCIIIIIICCRIIICCCCIIRIIIIICICCIIIIIIRCIIRCCICCCIIRCIIIIIIICIIIRICIIICRCIICIIICIIIICIIRIIRIIIICCIIIIIIRCCCIIIIIIRCCCIIICIIICIRIIIIIIIICRIIIIIICCIIICCRRIIICIIIRIIIIRIIIIIRIIIRIIIIIIIICIRCIIICCCCCIIRCCIIIIIIIRIICCCCICIIICIIRRCIIRCIIIICIIIIIIRIIIICIIICCCIIICCIIIIIIRCIRIIIIIIIICRIIIIIIIIICCRICRCIIIIIIICIIIIIIIICICRIIIIIIIIICCRICRCIIIIIICCIIIIIIRCIIIIIIICRICCRCIRCIIICCCCCIIRCCICCRIIIRIIIIRCIRIIIIIIIIIRIIIIIIIRCCIIICIICCRIICCIIICCIIIRCIRIIIICIIICIICCRIIIRICCIIIIICCCIIIRIIIIICRCRIIIIIRRCIIICIRIIIIRCIIIRRIIIICIICCRCICCIIIIIIRCIRIIIIIIIICRIIIIIIIRICCIIIIIIIIIRRRIIICIIIIIIIIIRIIIIIIIIIRIIIIIRIIRIICIIIICRIIICIIICIIIICIIRIIRCCCIIIIIIIIIRIIIIIIIICRICCRCICCIIIIIIRRIICCRRIIIIIIIIIIRCRICCRIIIRIIIIRCIIIIIIIIIIICCRCIIIIIIIIIIRIRIIICICIIIIIIIIIRIIIIRCIIIIIIICRIIICIIIRIIICCIRRCCCCRIIIICCRRCRCIIIIIIRCCCIIIIIIICRCIICCIIIICIIICCCIIIIIICCIIICCIIIIRIIIIRCIIIICIIIIICICRIIICIIIRRCIIIIIICCIICCCIIIIIIIRIIIIIIIRRRIIIIIIIIIIRIICIIIIIIIIIIICCIIIIRIIIIIIIIIRIIRIIRRCCIIIIIIIIIRIIIIRCIIIRCIIIIIIIIRIIIRCCIRRCICCRIIRCIIICCCCCIIRCCCIIIIIIICRIIIIIRIIIIIIIRRRCCCRIIIIIRIIIIIRIIIIIIIICIIICRCIIIIIICCIRRCCIRCIIIIRIIIRRCIIIIIIIIIIRIICIICIIIICIIICIIIIIIIIRIIIIIIIICRIIIIIIIIIIIIIICRCRIIIIIICRICCRCICCIIIIRIIICCCIRCCIIRIIIRIIIIRICCIIRCCIICIIIRCIIIRIIIIIICCCIIIIIIRRCRRIICCCIICCICCRCICCIIIIIIICIRCIIIIIIICRIIICCCCCIIIRRCIIICRCIIICIIIR

#87376
Participant

Morse code is for 19th-century throwbacks, amirite? Us hip modern folx
use prefix-free codes to transmit our messages. A prefix-free code is one
in which no codeword can be confused for the beginning of another codeword.

Here is an example. The code is a Huffman code for the 26 letters of English,
and is more efficient than ASCII or Bacon’s 5-digit binary code.

A 0001
B 001111
C 11001
D 1101
E 100
F 000001
G 000011
H 0110
I 0100
J 0000000101
K 00000000
L 00110
M 10111
N 0101
O 0010
P 001110
Q 00000001000
R 1010
S 0111
T 111
U 10110
V 0000001
W 11000
X 000000011
Y 000010
Z 00000001001

I encoded a short text with it. See if you can decode it.

000101101011000000100000110111000101011100100101101100010001110001001110
000110101110100110011011000110000110101110000100011101000010000001001000
111011101001011100010011000111010101000000010100000000011110010010110110
011101100001111010001111100100101011110111001001010011000001010110011110
011010000010010101000110001001110111001101000111011111010001111000111001
001010111001110101010001110111010000100101111011010000111010100010110011
000111011100100000010000010100010111010100010100001100101010101100111010
001010000110111101101100101100001110010010110110000111010100010110011001
001101011100111100001010111100000101010111001000000101101011000000100000
110111000101011100100101101010001010000110001010100010011000001100101010
010011101101011111011000000001100001100010001110100110100111100001011010
001000000101001101000101101011000000100000110111000101011100001100100001
101000110100110000001011100010111110011101011111110110110110001011110001
111101110100111000101011101001110101100011110011001000111011010011010100
010111101101000011100001001110100101000011011110011101100010110100000100
101010111011010011001001001010111111101010110110011110100001001010010000
001101110100010101001011110110101111010100110110110010111010001010111001
00001011001001011011000111

MD5 of text: ca70ea7b65a1c30a19e63d394204c847

Next, I made a new set of codewords. It is still prefix-free, but I won’t
tell you the codewords. It is not necessarily an efficient code, either.
I encoded another text. Let’s see if you can decode this:

011001111111111010110100111101101011010001000111100011110100101011010001
011010110110100111110100011111110100011110100111101111110001111010010101
101001011111010010111001110100111110010100111111100110110100110101101011
100111110100011111101011011110001101110111110111110100011000101101111010
101011001101111111110111010011101110100111000101011110011111110011111100
011110100101011010001101110001101010101101011101010101101011100110101101
110001010111000010110101111111001110100101011111111110100010110100111011
011111101111010010111011101001011101101011001111010011100010111101001111
011100111111100111010001111111111010110100111101101011010001000011111111
110101011110100011111110100111101011001111101000100111110011010110111100
111110011111101011010011000001011011110101101001011100111111100110110100
111001111111001110100111101011010001011010111110001011110100010011111001
101111010011101110100111100011110100101011010001000111101001111010110101
010110111000110011111110011101001011111010010111001110100111110010100111
111100110110100110101101011011001111111111010110100111101101011010001000
011110100111101010101101110001010110100110101100110111011101110100010111
111110010101001110001100110111101001111011011011100011110100011110100100
111111100111010011110101111100011110100101011010001000111101001111010110
101010110111000110011111110011101001011111010010111001110100111110010

#87392
The-Letter-Wriggler
Participant

For the first Huffman code
MD5: eb4d5c99f0e612590b51d7aa61775083 (All uppercase, no spaces + TLW)

#87393
The-Letter-Wriggler
Participant

Same key as your first code.
010011101000111100000101110000101000101001010110000011011011
100101011100010000000010011101100100011111001001011011000011
111011011100000001000101100100111100000101010010111011010010
101110110010001010000111110010110110011001001011011000100111

#87389
f6exb
Participant

I have the first but I don’t know how to start the other.

#87452
f6exb
Participant

Can we have a hint to decode the second message?

#87453
Participant

Hints?
It’s not Huffman, and is probably not efficient in any way.
The longest codeword is 9 bits.
If you make a binary tree, there is no guarantee that every leaf is a codeword or that there are only 26 leaves.
The first word of the plaintext is “A”.
The shortest codeword is 3 bits.

#87545
The-Letter-Wriggler
Participant

@person_314
I think we are going to need a hint for your ‘easy’ cipher.

#87551
f6exb
Participant

#87552
person_314
Participant

Sure. The cipher was created just after the royal cypher was released and uses the elements of the cypher “C” “R” and “III”. Try to find a way to manipulate the text to only contain these elements. And sorry for calling it easy, it is similar to this week’s challenge in difficulty.

#87553
person_314
Participant

Sorry to anyone who has attempted my challenge. I’ve just had a look at my original message and I have now realised why you can’t solve it. My hint above still applies but there was an error in my code and thus the encryption wasn’t working correctly. You should still have been able to get to a stage from which it seemed solvable but the last part was impossible to solve. Here is corrected cipher text (which this time hopefully will be easy (especially if you have already tried the original)): 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

#87549
Participant

@TLW,
RCIII
Rex Carolinus Tertius

#87548
f6exb
Participant

What I have found :
There is 2 same long strings (117 lettres): the 117 last letters of the cipher text and another before which start at 885.
So this give me the end of a code word (between 1002 an 1003) and the begining of another.
There are many strings of 9 and 10 letters “1”, but they are a combination of the end of a letter, a letter with many “1” and the begining of the next letters.
That’s all folks.

#87554
person_314
Participant

The problem is that I don’t think we can even be sure that the repetition guarantees that they are parsed to the same characters. It could just be the case that the beginning of one of the blocks extends one character before and then you end up parsing the repeated parts completely differently. This is probably not the case for this repetition and the repetition most likely corresponds to repetition in the plain text, but we can’t be sure. In the general case repetitions not at the end of the text are annoying because we don’t know where the code word ends (the code words for either repetition could extend for more characters past the repeated section). The whole problem seems very NPish and its not like we can find decent approximate solutions by starting with a random code and then hill climbing to a better answer because a random modification won’t necessarily be prefix-free.

I can also see no way forward, and if madness (or someone who has had more luck/skill with this than me) would like to give further advice that would be most appreciated.

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