HFGCS · Group 4 long messages · 243 of 60+ characters · 221116 – 261012

Long G4 Block Layout

Positions count from 1. Every row except the prefix and the trailer ends in a marker. Messages are labelled by date (YYMMDD), time (UTC), prefix and length, like 261004 21:38z MM-164.

Rows

RowPositionsClosed byEvidence
Prefix1–2—Shared by every message of the prefix.
A3–24X??X21 = 24 in 179 of 205 messages of 100+ characters (87%; chance is about 3%).
B25–45quadQuad at 42–45 in 162 of the same messages (79%). Four equal characters at a fixed spot almost never happen by chance.
Blocks46–67, 68–89 …quad18 characters + quad, repeated.
Insertinside a blockX??X, quad16 extra characters that stretch one block to 38. 40 of the 47 inserts split the way rows A and B do, only shorter: 13 + X??X, then 17 + quad.
Trailerlast 9—The last block's quad sits right before it in 84 of 109 plain messages and 38 of 41 with an insert. Other families end differently. Its first two characters are the head of the field that comes next in the prefix's order: 62 of the 68 messages that end on a quad-closed field (chance 0.1%); see below.

The trailer points ahead

A message carries the first n fields of its prefix's list, and the trailer opens with the two-character head of field n + 1. MM-224 ends where MM-246 goes on: its trailer opens E7, and the 246 carries the E7YTJ field in that slot. Across the prefixes, 62 of the 68 messages that end on a quad-closed field do this (chance 0.1%); positions 3 to 9 of the trailer agree with nothing tested so far. Two characters are enough: within a prefix, 515 of 520 two-character heads name a single field. Where a message ends in a ##-run, a stub or an extra head the rule mostly fails (2 of 38), so those endings do something else.

260912 16:51z MM-224 → 261012 17:05z MM-246 · offset +0 · z 43.0 · row B and blocks 1–6, the 224's trailer E7 under the start of the 246's row 7
3
DTKYN5JK3RLDKQ2CIPQK7Q
UALZQEICERQWUF2CGPQX7Q
22row A
25
EYTAC4MBQP26N4B4TOOOO
EYTAI4QBMP2O466TBOOOO
21row B · from its row B
46
PFGBCAHGZZ362LGR6LAAAA
PFGBCVHOHA36QG262JAAAA
22block 1 · from its block 1
68
74ZLMVJXJ47JATMTMFKKKK
74ZLMEJJMK7JQMJNJAKKKK
22block 2 · from its block 2
90
BLCOP2ANNPQV7DI677GGGG
BLCOPDAADPQVUK77UIGGGG
22block 3 · from its block 3
112
2NF6W3SU2R3QDIO6I
2NF6HXZD2R36DIK7I
17row A′
129
3EGSD3XJXPBGWBGC5TTTT
3EGSQX7XDPBGWWBBBTTTT
21row B′
150
VMV4OFEMEB3UXUNN6AQQQQ
VMV4O7ZZHE3UX664AWQQQQ
22block 4 · from its block 4
172
DSQ4IFBLB35SWSPIPQPPPP
DSQ4INUBBN5SWOOPWWPPPP
22block 5 · from its block 5
194
ZVZW7HSRO7DXQXL353FFFF
ZVZW7OTTCRDXQ553XSFFFF
22block 6 · from its block 6
216
E7YTJPNXXLDI2IR7R2EEEE
E7CIWO6N3             
22block 7
238
SNXQQVTCZ
         
9trailer

Which row each marker closes

You can tell which row a marker belongs to by what gets copied along with it:

A quad that wasn't copied would match only about 3% of the time. So each quad closes the block that comes before it, and the X??X at 21–24 closes row A.

Positions 3–16 of row A match their source only at chance level: 46 of 1,420 (3.2%). The end of row A sometimes comes along with row B: in the 59 matches that take row B, positions 17, 20, 21 and 24 match 20, 19, 19 and 16 times.

Length families 201 of 205 at 100+ characters fit

Each variant adds a fixed number of characters to 54 + 22n. 201 of the 205 messages of 100+ characters fit one of these; 4 don't. The 38 under 100 are just listed by length, since most of them have no quads.

FormExtraLengths seen (×count)Messages
54 + 22nplain120×39, 142×40, 164×23, 186×6108
70 + 22none 16-character insert158×3, 180×2, 202×3, 224×4, 246×9, 268×8, 290×231
56 + 22nlast two blocks replaced by 17 + a 29-character run (most 166s, the 188), or head 46 longer (one 166, the 210)166×12, 188, 21014
72 + 22nhead 40 longer (one 160, the 182s, the 204), or 18 extra further on (the other 160s, the 292)160×4, 182×2, 204, 2928
62 + 22n52 extra: in the head for some 216s, at the end for the rest172×8, 194×3, 216×1425
68 + 22nhead 40 longer and 18 more at the end (the 222s)222×22
66 + 22n12 extra176, 198, 220, 286×25
64 + 22ntwo inserts108×5, 152, 196, 2188
—none of these102×2, 118×24
under 100by length only60×3, 62×10, 66, 68×11, 70, 76, 84, 92×9, 9438

Kept and changed positions 394 reused blocks

Here's how often each position of a reused block matches its source, over the 394 blocks reused in direct matches (a block counts as reused when at least 6 of its 22 characters match):

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Q
Q
Q
Q

1–18 are the block's characters and Q its closing quad. Pink = kept (1–5, 11–13 and the quad, 89% match). Grey = changed (6–10 and 14–18, 16%). Chance is 3.2%.

Position 4 matched in all 394, and position 11 in 393. The changed positions still match about 5 times as often as chance (16% against 3.2%), so some of their characters carry over too. The block families show it with the copies stacked up.

Reused blocks or a repeating key?

If this were a key repeating every 22 or 44 characters, two aligned messages would match at a steady rate all the way along. They don't:

Examples

Each card shows the later message row by row, with the earlier one lined up underneath (at +44, position p of the earlier message sits under position p + 44 of the later one). The right column says which row of the earlier message each reused stretch came from.

same characterquadleft number = row start in the later message
260902 21:07z MM-180 → 261004 21:38z MM-164 · offset +44 · z 23.5 · row B and blocks 1–3, two slots further on
3
V4MNSRJISBSI6L5YPHJTAJ
                      
22row A
25
IGTJILNINDI2X2AAQEEEE
                    M
21row B
46
SNDNSHHSGSXKPGPGNGUUUU
M2K7B4MA7SZ7KZQXDXQLIS
22block 1
68
7NILZIIT3ASPORRLRNLLLL
L46LZYIA6ASRBARBBALLLL
22block 2 · from its row B
90
CPPCSOOKIVACBHHHHHWWWW
CPPCSFOISTAHM3HGHGWWWW
22block 3 · from its block 1
112
SG7F2DD3BIOGSJGWHJGGGG
SG7F2ADD2IOJHIJIG6GGGG
22block 4 · from its block 2
134
X75B7222QWEHSDHSQ27777
X75B7P2M2AED2VDV2W7777
22block 5 · from its block 3
156
2SYL5KTFH
2SNCTPM43
9trailer
260909 21:23z MM-120 → 261005 21:50z MM-180 · offset +44 · z 17.8 · row B and blocks 1–2, two slots further on
3
GHPQ23XHEDIT5AXDHRIYCI
                      
22row A
25
JQCT4MKMTCLFF3FLFXXXX
                    M
21row B
46
FRZCOXQHOQJ4TT6YNPIIII
MNGPCOHDOHSEFAB7FYXORW
22block 1
68
LQRO6M6AWA7XGGHSGY4444
OXTOAATDVX7XGXHGYB4444
22block 2 · from its row B
90
VILNORORLG3Q77Q767YYYY
VILNLLHBJO3Q7QEBBQYYYY
22block 3 · from its block 1
112
7PNE2XUFG226QQIZWQJJJJ
7PNEUU7ZZ726Q6IIWBJJJJ
22block 4 · from its block 2
134
WOLOY3BNJ3G2NTAHT
WOV3NNYSYNHRNROON
17row A′
151
KJ3OECICIHRNCNRKQLLLL
RLLLLDIWHLLLEQ       
21row B′
172
DIWHL7PTQ
         
9trailer
260901 21:08z MM-186 → 260912 16:51z MM-224 · offset +82 · z 26.5 · blocks 1–4, three slots further on plus the 16-character insert (66 + 16 = 82)
3
UALZQEICERQWUF2CGPQX7Q
                      
22row A
25
EYTAI4QBMP2O466TBOOOO
                     
21row B
46
PFGBCVHOHA36QG262JAAAA
                      
22block 1
68
74ZLMEJJMK7JQMJNJAKKKK
               MM6OBF4
22block 2
90
BLCOPDAADPQVUK77UIGGGG
2BLAYHRVAAREYZU4ZIHOPY
22block 3
112
2NF6HXZD2R36DIK7I
AD7AQVU74IIZGGGG2
17row A′
129
3EGSQX7XDPBGWWBBBTTTT
NVGS73SSDPBGWCBTBTTTT
21row B′ · from its block 1
150
VMV4O7ZZHE3UX664AWQQQQ
VMV4ODEZM73UX6AO6UQQQQ
22block 4 · from its block 2
172
DSQ4INUBBN5SWOOPWWPPPP
DSQ4I2BBNB5SWO6POWPPPP
22block 5 · from its block 3
194
ZVZW7OTTCRDXQ553XSFFFF
ZVZW7QDOCHDXQ5AS3LFFFF
22block 6 · from its block 4
216
E7CIWO6N3
E7YTJBN5D
9trailer

Built 261022 from SHORTWAVES. A long G4 is a Group 4 message of 60 characters or more, first airing only, without partial captures or disregarded reads. Positions count from 1. Generated by eam_block_pages_.py.