Solution
A: HELLO_LUSAKA
A: CAN_YOU_HEAR_ME
B: HELLO_HARARE
B: LOUD_AND_CLEAR
A: TEST_TEST_ONE_TWO_THREE
B: THE_QUICK_BROWN_FOX_JUMPS_OVER_THE_LAZY_DOG
A: BUFFALO_BUFFALO_BUFFALO_BUFFALO_BUFFALO_BUFFALO_BUFFALO_BUFFAL (yes, the last O is missing)
B: JAMES_WHILE_JOHN_HAD_HAD_HAD_HAD_HAD_HAD_HAD_HAD_HAD_HAD_HAD_A_BETTER_EFFECT_ON_THE_TEACHER
A: TIME_FLIES_LIKE_AN_ARROW_FRUIT_FLIES_LIKE_A_BANANA
B: THAT'S_ONE_SMALL_STEP_FOR_A_MAN_ONE_GIANT_LEAP_FOR_MANKIND
A: HOUSTON_WE_HAVE_A_PROBLEM
B: HAHA
A: SPIDER_PIG_SPIDER_PIG
A: THE_TEST_WAS_SUCCESSFUL
A: HARARE_OUT
B: HEAR_YOU_TOMORROW
Key
In alphabetical shifts, the key is BOBDPOE (Bob D. Poe?).
In numerical shifts, the key is 1 14 1 3 15 14 4.
I only needed the first 7 so there could be more.
Countries of the participants
Lusaka is the capital of Zambia and Harare is the capital of Zimbabwe, so A is from Zimbabwe and B is from Zambia.
Reverse-Engineered Ciphering Process
Let's encode "ABCDEFG". We start with the first letter.
- A
This is line one.
On the next line we are going to write the next two letters on either side of the A:
- A
- B C
"B C" is line two. You may be wondering why I am not just writing this as "BAC". That's because we are going to shift the "A" and the "B C" independently of each other.
Next we write "DEFG" between the previous letters.
- A
- B C
- D E F G
Now each line has to be shifted by the corresponding letter of the keyword: B, O, B.
- A [Shift by B]
- B C [Shift by O]
- D E F G [Shift by B]
becomes
- B [Shift by B]
- P Q [Shift by O]
- E F G H [Shift by B]
We then read the message from left to right to obtain the ciphertext.
- B [Shift by B]
- P Q [Shift by O]
- E F G H [Shift by B]
- EPFBGQH
Now let's apply this to the original messages.
- HELLO_LUSAKA
- H [Shift by B]
- E L [Shift by O]
- L O _ L [Shift by B]
- U S A K A [Shift by D]
- XMVSDPNID_ZM
- CAN_YOU_HEAR_ME
- C [Shift by B]
- A N [Shift by O]
- _ Y O U [Shift by B]
- _ H E A R _ M E [Shift by D]
- __KOHZDDUP_BPVH
- HELLO_HARARE
- H [Shift by B]
- E L [Shift by O]
- L O _ H [Shift by B]
- A R A R E [Shift by D]
- DMUSDPUIH_ZI
- LOUD_AND_CLEAR
- L [Shift by B]
- O U [Shift by O]
- D _ A N [Shift by B]
- D _ C L E A R [Shift by D]
- GE_CF_OMHBDIUO
- TEST_TEST_ONE_TWO_THREE
- T [Shift by B]
- E S [Shift by O]
- T _ T E [Shift by B]
- S T _ O N E _ T [Shift by D]
- W O _ T H R E E [Shift by P]
- LVDU_WISW_G_TRTUQUHG_FW
- THE_QUICK_BROWN_FOX_JUMPS_OVER_THE_LAZY_DOG
- T [Shift by B]
- H E [Shift by O]
- _ Q U I [Shift by B]
- C K _ B R O W N [Shift by D]
- _ F O X _ J U M P S _ O V E R _ [Shift by P]
- T H E _ L A Z Y _ D O G [Shift by O]
- H_VFSU__ZDONNMMV__R_CYURJEBUEUHV_RDSKZTJGQ_
- BUFFALO_BUFFALO_BUFFALO_BUFFALO_BUFFALO_BUFFALO_BUFFALO_BUFFAL (yes, the last O is missing)
- B [Shift by B]
- U F [Shift by O]
- F A L O [Shift by B]
- _ B U F F A L O [Shift by D]
- _ B U F F A L O _ B U F F A L O [Shift by P]
- _ B U F F A L O _ B U F F A L O _ B U F F A L O _ B U F F A L [Shift by O]
- __P_IQTGTJOEZUCI_UPXIPTBTAOIZDCC__PIIQTMTJODZUCT_UPOIPTPTAORZD
- JAMES_WHILE_JOHN_HAD_HAD_HAD_HAD_HAD_HAD_HAD_HAD_HAD_HAD_HAD_A_BETTER_EFFECT_ON_THE_TEACHER
- J [B]
- A M [O]
- E S _ W [B]
- H I L E _ J O H [D]
- N _ H A D _ H A D _ H A D _ H A [P]
- D _ H A D _ H A D _ H A D _ H A D _ H A D _ H A D _ H A D _ A _ [O]
- B E T T E R _ E F F E C T _ O N _ T H E _ T E A C H E R [E]
- FRICX_XKIVV__OIFJRJWI_GLXV_PSORO_RXSL_IO_VX_IOETGRLWI_VHVPOKRS__V_O_RW_MVPOARS_RV_OXRW_KOP_
- TIME_FLIES_LIKE_AN_ARROW_FRUIT_FLIES_LIKE_A_BANANA
- T [Shift by B]
- I M [Shift by O]
- E _ F L [Shift by B]
- I E S _ L I K E [Shift by D]
- _ A N _ A R R O W _ F R U I T _ [Shift by P]
- F L I E S _ L I K E _ A _ B A N A N A [Shift by O]
- T_ZLWPSFGC_HZ_WWYPSV_GO__GP_ODBUOLBOO_GULGAJNXMIH_
- THAT'S_ONE_SMALL_STEP_FOR_A_MAN_ONE_GIANT_LEAP_FOR_MANKIND
- T [Shift by B]
- H A [Shift by O]
- T ' S _ [Shift by B]
- O N E _ S M A L [Shift by D]
- L _ S T E P _ F O R _ A _ M A N [Shift by P]
- _ O N E _ G I A N T _ L E A P _ F O R _ M A N K I N D [Shift by O]
- _ACRB_SU_HUQWIOVBTHH_EZ'S_O_DU_UTDCVFG_TA_OPBPYOW_BDRB_POC
- HOUSTON_WE_HAVE_A_PROBLEM
- H [Shift by B]
- O U [Shift by O]
- S T O N [Shift by B]
- _ W E _ H A V E [Shift by D]
- _ A _ P R O B L E M [Shift by P]
- __PT_ZECGHDUQ_AITKBPDIYOH
- HAHA
- H [Shift by B]
- A H [Shift by O]
- A [Shift by B]
- BOIV
- SPIDER_PIG_SPIDER_PIG
- S [Shift by B]
- P I [Shift by O]
- D E R _ [Shift by B]
- P I G _ S P I D [Shift by D]
- E R _ P I G [Shift by P]
- TSGE_LEDXJVF_TVSSWL_G
- THE_TEST_WAS_SUCCESSFUL
- T [Shift by B]
- H E [Shift by O]
- _ T E S [Shift by B]
- T _ W A S _ S U [Shift by D]
- C C E S S F U L [Shift by P]
- RWR_T_HVHZUUJDAUVF_SVTX
- HARARE_OUT
- H [Shift by B]
- A R [Shift by O]
- A R E _ [Shift by B]
- O U T [Shift by D]
- RBXOWSIFF_
- - HEAR_YOU_TOMORROW
- - H [Shift by B]
- - E A [Shift by O]
- - R _ Y U [Shift by B]
- - U _ T O M O R R [Shift by D]
- - O W [Shift by P]
- - DXLS_SW_RIPZROUPU
Reverse-Engineered Deciphering Process
It is horrendous to manually decipher with the key.
First you have to count the number of characters:
T_ZLWPSFGC_HZ_WWYPSV_GO__GP_ODBUOLBOO_GULGAJNXMIH_
We have 50 characters here. Now we have to map out slots for the characters based on that number (notice how skewed it is according to the length of the last line). The numbers are going from left to right.
- 2
- 6 3
- 8 4 9 7
- 4 2 0 8 6 1 5 9
- 2 6 0 4 8 2 6 0 4 8 0 2 4 6 8 0
-1 3 5 7 9 1 3 5 7 9 1 3 5 7 9 1 3 5 7
We insert the ciphertext:
- T_ZLWPSFGC_HZ_WWYPSV_GO__GP_ODBUOLBOO_GULGAJNXMIH_
- U
- W A
- F _ G M
- L H V _ O L N H
- _ P C _ P G G D L _ U G J X I _
- T Z W S G _ Z W Y S _ O _ P O B O B O
Finally we unshift each line by the corresponding letter of the key:
- T_ZLWPSFGC_HZ_WWYPSV_GO__GP_ODBUOLBOO_GULGAJNXMIH_
- T [Unshifted by B]
- I M [Unshifted by O]
- E _ F L [Unshifted by B]
- I E S _ L I K E [Unshifted by D]
- _ A N _ A R R O W _ F R U I T _ [Unshifted by P]
- F L I E S _ L I K E _ A _ B A N A N A [Unshifted by O]
- TIME_FLIES_LIKE_AN_ARROW_FRUIT_FLIES_LIKE_A_BANANA
Reasoning
This is the result of many, many all-nighters. I have been working on this since I joined the site a month ago.
Most of the work was of course ruling out what it wasn't. I had to keep repeating Edison's quote to myself: "I have not failed. I've just found 10,000 ways that won't work."
The first major breakthrough was observing that taking the first of every two characters of certain lines, I would find repeated sequences, such as __P_IQT... becoming _PITTOZC_PITTOZC_PITTOZC_PITTOZ.
FRICX_XKIVV__OIFJRJWI_GLXV_PSORO_RXSL_IO_VX_IOETGRLWI_VHVPOKRS__V_O_RW_MVPOARS_RV_OXRW_KOP_
becomes
FIXXIV_IJJIGX_SR_XLI_XIEGLIVVOR_VOR_VOR_VOR_O_
The second major breakthrough was observing that, with the above line, if I took the first of every two letters, then took the second of every two letters, then stitched these together,
FIXXIV_IJJIGX_SR_XLI_XIEGLIVVOR_VOR_VOR_VOR_O_ + RC_KV_OFRW_LVPOORS_OV_OTRW_HPKS___WMPASR_XWKP
then removed VOR_VOR_VOR_VOR,
FIXXIV_IJJIGX_SR_XLI_XIEGLIV_O_ + RC_KV_OFRW_LVPOORS_OV_OTRW_HPKS___WMPASR_XWKP
then repeated the split/stitch again,
FXI_JIXS_L_IGI__CK_FWLPOSO_TWHK__MARXK + IXVIJG_RXIXELVOR_VOR_VOR_VOR_PS_WPS_WP
I saw VOR_VOR_VOR_VOR again. There seemed to be some sort of nesting involved.
The third major breakthrough was observing that nested split/stitching __P_IQT... resulted in
_QJUUPAD_QJUUPAD
The fourth major breakthrough was observing that, when we took the first of every two characters of every line, the result had no double spaces.
XVDNDZ
_KHDU_PH
DUDUHZ
G_FOHDU
LD_IWGTTQH_W
HVS_ZONM_RCUJBEH_DKTG_
_PITTOZC_PITTOZC_PITTOZC_PITTOZ
FIXXIV_IJJIGX_SR_XLI_XIEGLIVVOR_VOR_VOR_VOR_O_
TZWSG_ZWYS_O_POBOBOGLANMH
_CBS_UWOBH_ZSOD_TCF_AOBYWBR_O
_P_EGDQATBDYH
BI
TG_EXV_VSLG
RRTHHUJAV_VX
RXWIF
DL_WRPRUU
For a long time, however, this was a dead end.
The fifth major breakthrough
Then suddenly, by some fluke of the universe, I noticed that PITTOZC could shift to QJUUPAD.
And that both could shift to BUFFALO.
BOOM. Something meaningful.
Googled "buffalo buffalo buffalo buffalo". IT'S A THING.
The sixth major breakthrough was going through all the first-letter halves and seeing if I could shift them to anything meaningful.
I could.
I found the following fragments:
USAKA (LUSAKA, ZAMBIA)
HEAR_ME
ARARE (HARARE, ZIMBABWE)
D CLEAR
THE LAZY DOG
BUFFALO BUFFALO BUFFALO BUFFAL
BETTER_EFFECT_ON_THE_TEACHER
FLIES_LIKE_A_BANANA
ONE_GIANT_LEAP_FOR_MANKIND
A_PROBLEM
CCESSFUL
OUT
Seventh major breaththrough
Lots of these were clearly fragments of mic-check phrases. The confirmation of this was realising that all of them other than the BUFFALO one were exactly the right length:
THE_QUICK_BROWN_FOX_JUMPS_OVER_THE_LAZY_DOG
H_VFSU__ZDONNMMV__R_CYURJEBUEUHV_RDSKZTJGQ_
JAMES_WHILE_JOHN_HAD_HAD_HAD_HAD_HAD_HAD_HAD_HAD_HAD_HAD_HAD_A_BETTER_EFFECT_ON_THE_TEACHER
FRICX_XKIVV__OIFJRJWI_GLXV_PSORO_RXSL_IO_VX_IOETGRLWI_VHVPOKRS__V_O_RW_MVPOARS_RV_OXRW_KOP_
TIME_FLIES_LIKE_AN_ARROW_FRUIT_FLIES_LIKE_A_BANANA
T_ZLWPSFGC_HZ_WWYPSV_GO__GP_ODBUOLBOO_GULGAJNXMIH_
THAT'S_ONE_SMALL_STEP_FOR_A_MAN_ONE_GIANT_LEAP_FOR_MANKIND
_ACRB_SU_HUQWIOVBTHH_EZ'S_O_DU_UTDCVFG_TA_OPBPYOW_BDRB_POC
HOUSTON_WE_HAVE_A_PROBLEM
__PT_ZECGHDUQ_AITKBPDIYOH
Eighth major breakthrough
If the original text hadn't had the mistake of the missing O of the last BUFFALO, I would have worked out sooner that the start of each of the fragments from Breakthrough Six was the end of each message.
Ninth major breakthrough
This took a very long time, but I finally cracked the exact process with writing out CAN_YOU_HEAR_ME. Up until now, I had noticed that there was some nesting, but I had always hit a dead-end getting to the bottom of it. I got lucky with this message because it happens to be the exact length required that there is no space on the last line, which would have skewed it.
- CAN_YOU_HEAR_ME
- C [Shift by B]
- A N [Shift by O]
- _ Y O U [Shift by B]
- _ H E A R _ M E [Shift by D]
- __KOHZDDUP_BPVH
From here, I was finally able to read the rest of the messages.
One Last Thing To Do: Name of the Cipher
Using the cipher, BFTIODFTTWKBCSC decodes into SUNECVRYQLCQHZZ.
- SUNECVRYQLCQHZZ
- T [Shift by B]
- I B [Shift by O]
- F D W S [Shift by B]
- B T O F T K C C [Shift by D]
- BFTIODFTTWKBCSC
You're telling me that the title uses a different cipher? Are you mental? If it is remotely as difficult and obscure as this cipher was, it will be basically impossible to work out using just one line. I have no idea. I have tried lots of things but can't make sense of it. I will update this and give credit to whoever figures this out.
Probably coincidentally, BFTIODFTTWKBCSC and PROJECTANACONDA are the same length and have the same letter frequency rates.
Notes
1. I entirely misinterpreted this clue:
"most likely some standard phrases will be used in the test conversations"
to mean that there would be some standard MILITARY phrases. But no, this meant mic check style phrases. I personally think it would be been a better puzzle if there had been a normal conversation happening.
2. I tried for so long to think of what "BOIV" could turn into - sure, okay, good, done, true, yeah, etc - but never guessed "Haha".
3. The last O in the last Buffalo is missing. It is unclear whether it went missing when writing the original message or writing its ciphertext, since it thankfully happens to be in the one location where it would have no effect on the result (the end).
4. No idea what the rap clue is about. When I had only worked out the first four letters of the key, I thought the lyric format might be a clue and thought, hmmm, BOBD = Boulevard of Broken Dreams? Alas. Had a nice experience listening to some old bands again though.
_represents a space for legibility reasons.) $\endgroup$