Headline Cipher

Introduction

2012-08-19T09:38:50+00:00

The Headline puzzle was first published in 1964 in the monthly US National Security Agency newsletter. The readership included the top cryptanalysis brains of the time and so the puzzle had to be tip-top. It was. It had a number of dimensions, each of which required a different crypto skill from decipherment through key recovery to word recognition. Although reputedly just a ‘lunch-time puzzle’ at the NSA, it holds far more of a challenge for the rest of us.

There were no personal computers in 1964 so solving was done with pencil and paper, perhaps supported by pattern word lists. Nowadays, however, the computer makes short work of finding the solution. Perhaps five minutes is the maximum it need take, though in some cases one minute is nearer the mark.

This makes solving sound like shooting fish in a barrel. What’s the point in doing such an easy thing? The answer is that it’s the chase that’s the fun, not the kill. The task of thinking through a suitable algorithm and then developing the computer program to implement it is where the fun lies. Once that is done solving is admittedly a doddle – until a puzzle turns up with an unexpected twist that defeats the computer. And then the fun begins again, to massage the algorithm and the program to take into account this new feature.

Those who are interested in the Headline puzzle (both computer solvers and the many pencil & paper solvers) will find all the information and guidance they could want at Jude’s website. In this website of mine, I confine myself to enough detail to explain how the puzzle works – and then challenge you to develop your own program to solve it.

Just in case you need help, I explain my way of going about it though the beauty of the puzzle is that there are a number of ways in. I also provide a couple of working programs just in case you want proof from the outset that the computer is fully capable of solving.

Outline of Headline Cipher

2012-08-19T09:42:56+00:00

The Headline puzzle enciphers five newspaper headlines with a matrix derived from a Keyword, a Hat and a Setting. Here is an example:

Keyword: JAVELIN
Hat: BALLISTA
Setting: SWORD

A key block is set up from the Keyword and then stripped by columns in order determined by the Hat to form the mixed alphabet:

BALLISTA
31564782
JAVELINB
CDFGHKMO
PQRSTUWX
YZ

Mixed alphabet: ADQZBOXJCPYLHTVFREGSIKUNMW

Finally the enciphering matrix is built from the mixed alphabet and the Setting. The mixed alphabet forms the top row, representing plaintext characters. The Setting is written vertically in rows 1 to 5, below the first letter of the mixed alphabet. Then the remainder of the mixed alphabet is written in:

plain adqzboxjcpylhtvfregsikunmw
row1 SIKUNMWADQZBOXJCPYLHTVFREG
2 WADQZBOXJCPYLHTVFREGSIKUNM
3 OXJCPYLHTVFREGSIKUNMWADQZB
4 REGSIKUNMWADQZBOXJCPYLHTVF
5 DQZBOXJCPYLHTVFREGSIKUNMWA

The first headline is enciphered with row 1, the second with row 2 and so on. The five Headlines:

Third Estate decrees National Assembly.
King orders closure of Estates.
Crowd runs riot, Bastille stormed.
Violence against nobles as many flee.
Citizen Louis Capet guillotined.

Encipher to:

XOTPI YHXSXY IYDPYYH RSXTMRSB SHHYENBZ.
ISUE BFARFG JYBGKFR BV RGHWHRG.
TKYBX KDQM KWYG, POMGWRRU MGYKZUX.
BYKDJTMJ RCRYTPZ TKIDJP RP VRTA ODJJ.
PKVKBGM HXNKI PDYGV SNKHHXVKMGQ.

Can you solve the headlines with your computer?

2012-08-19T09:44:39+00:00

The puzzle comprises enciphered Headlines. No other information is given. Here is an example:

(1) GJSUJD GDCUUSU DHNPGCE: USEJIS TOSSU PE XJEPG.
(2) BMKKLRK DMK GHMU MUJ DRUNAI GVVQ.
(3) YVWPX FATXL KEVPAPF EIWOQ ABXL WD HEVYC.
(4) VKSFSE TBOKTZTBQFNR TB HTXXNK IXLF
(5) TWJA WHLBHP VWTKHLR WHZ UBJJBIR KWJR.

The first step is to decipher the headlines. Can you do it? If you can’t then read below.

Can you recover the matrix & Setting?

2012-08-19T09:45:29+00:00

Having solved the headlines we can construct a partial matrix of plain and cipher equivalents for each headline. From this can you recover the full matrix and the Setting? If not, read on below.

Can you recover the Key & Hat?

2012-08-19T09:51:49+00:00

The third step is to recover the mixed alphabet, then the Key and the Hat. Your computer can do this if you give it a suitable program. Can you do this? If not then read on.