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This is my first self-developed cryptographic puzzle. I hope it is neither too hard nor too easy for you to break, and that you enjoy it. Please do not only post the answer, but also your way towards it.


You are Alan Turing 2.0 - a British intelligence officer trying to break newly created codes from around the world.

Based on intelligence gained by turning a Zambian cipher clerk, you are right now listening in on a test run of a Zambian-Zimbabwian ciphered exchange, codenamed "Project Anaconda", using a newly developed cipher going by the cryptic name of "BFTIODFTTWKBCSC".

The cipher clerk delivered to you

  • the name(s) of the cipher,
  • the route used, so your technicians could listen in and report to you the text transmitted,
  • that the cipher requires a key that the clerk does not get to see, but that to his knowledge only a single key has been agreed upon during a meeting by the three-star generals overseeing the whole operation,
  • that his input terminal had 29 keys: the alphabet, the space, the apostroph and the enter key, and a mode switch to select "Encrypt" or "Decrypt", but neither Shift nor numeric keys.
  • that most likely some standard phrases will be used in the test conversations.

No other useful information could be gained until now; the interrogator will report to you at once if he gains anything valuable.

The technicians reported that the line has gone live only after they tapped into it.

Your objectives:

  • Decipher the test messages.
  • Determine the key(s) used.
  • Reverse-engineer the algorithm.
  • Decipher the algorithm name.
  • If possible, determine the respective country of the correspondents A and B.

The test messages reported by your technicians until now were the following:

A: XMVSDPNID_ZM
A: __KOHZDDUP_BPVH
B: DMUSDPUIH_ZI
B: GE_CF_OMHBDIUO
A: LVDU_WISW_G_TRTUQUHG_FW
B: H_VFSU__ZDONNMMV__R_CYURJEBUEUHV_RDSKZTJGQ_
A: __P_IQTGTJOEZUCI_UPXIPTBTAOIZDCC__PIIQTMTJODZUCT_UPOIPTPTAORZD
B: FRICX_XKIVV__OIFJRJWI_GLXV_PSORO_RXSL_IO_VX_IOETGRLWI_VHVPOKRS__V_O_RW_MVPOARS_RV_OXRW_KOP_
A: T_ZLWPSFGC_HZ_WWYPSV_GO__GP_ODBUOLBOO_GULGAJNXMIH_
B: _ACRB_SU_HUQWIOVBTHH_EZ'S_O_DU_UTDCVFG_TA_OPBPYOW_BDRB_POC
A: __PT_ZECGHDUQ_AITKBPDIYOH
B: BOIV
A: TSGE_LEDXJVF_TVSSWL_G
A: RWR_T_HVHZUUJDAUVF_SVTX
A: RBXOWSIFF_
B: DXLS_SW_RIPZROUPU

Good luck, Mr. Turing.

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  • 1
    $\begingroup$ @TrojanByAccident I have clarified some things about the input terminal. (Given that the transmitted ciphertext has to be reentered by a clerk for decryption, you may assume that the _ represents a space for legibility reasons.) $\endgroup$ – Alexander Jan 13 '17 at 3:58
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    $\begingroup$ @Techidiot The cipher is a standard cipher with two "improvements" by me, because the standard cipher in itself is not suitable for a puzzle on this site. I sincerely believe the resulting algorithm can be broken using basic cryptanalysis and a bit of internet search. $\endgroup$ – Alexander Jan 14 '17 at 7:59
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    $\begingroup$ Have any hints? $\endgroup$ – internet_user Jan 11 '18 at 16:51
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    $\begingroup$ It would be nice to have some hint! $\endgroup$ – IdkWhy May 8 '18 at 15:05
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    $\begingroup$ that the cipher requires a key // that the clerk does not get to see, // but that to his knowledge only // a single key // has been agreed // upon during a meeting // by the three // star generals overseeing // the whole operation. That would be a nice rap. $(+1)$ :D $\endgroup$ – Mr Pie Oct 7 '18 at 6:48

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