In May 2014 the NSA published four crypto challenges via Twitter. To my knowledge, the fourth one is still unsolved.
You want to win a copy of Helen Fouché Gaines’ book Cryptanalysis? If so, try to solve one of the following crypto challenges:
Send your solutions to email@example.com by the end of January with your name to be in to win. Early February two random entries will be drawn. The competition is organized by blog reader Bart Wenmeckers on the occasion of the second aniversary of the Cryptograms & Classical Ciphers FaceBook group. Please don’t publish the solutions before the competition is finished.
NSA’s Monday challenges from 2014
Let’s now turn to four other crypto challenges. They were published by the NSA on Twitter (@NSACareers, #MissionMonday) in May 2014. The first three challenges were of medium difficulty, at best:
Challenge #1 (Monday, May 5th, 2014)
tpfccdlfdtte pcaccplircdt dklpcfrp?qeiq lhpqlipqeodf gpwafopwprti izxndkiqpkii krirrifcapnc dxkdciqcafmd vkfpcadf.
Solution (letter substitution): want to know what it takes to work at nsa? check back each monday in may as we explore careers essential to protecting our nation.
Challenge #2 (Monday, May 12th, 2014)
Solution (letter substitution, plaintext has to be read backwards): NSA is looking for intelligent, imaginative critical thinkers who can contribute innovative ideas to solve our most difficult challenges.
Challenge #3 (Monday, May 19th, 2014)
Solution (letter substitution, plaintext in Spanish): Los cient(i)ficos de la computaci(o)n tienen la oportunidad de ampliar sus iniciativas, habilidades y talentos para aprender y ser imaginativos.
As can be seen, all three solutions explain the purpose of these challenges. The NSA published them in order to attract skilled codebreakers that might be interested in a career at the agency. However, the first three cryptograms were not difficult enough to challenge the really good ones. This changed with the fourth challenge.
Still unsolved: challenge #4
The fourth ciphertext (Monday, May 26th) proved quite difficult. Here it is:
I blogged about this challenge in 2014 (in German). Though there were a number of comments, nobody could break this cryptogram. Almost four years later, I’m still not aware of a solution. When searching via Google, I can’t even find a page describing the challenge, let alone the cleartext.
Here’s a frequency analysis made with CrypTool 2:
This looks like an ordinary MASC (monoalphabetic substitution cipher). The Index of Coincidence (IoC) is 6.7 percent, which is consistent with the English language. As the B is the most frequent letter, it might stand for the E. However, I don’t think that it is that simple – otherwise the challenge would have been long solved.
Does a reader know whether the solution of this challenge is available somewhere? If not, can a reader break it?
Further reading: A few videos and crypto puzzles from the NSA Symposium on Cryptologic History