scp81: fix RAM LOAD block splitting (overlapping 1-byte shifts) (v2.1.12)

The block slicer used the block number as a character offset
(loadfile_tlv[i * 2:(i + 240) * 2]), so every LOAD block after the first was
a 1-byte-shifted copy of the previous one - the cap header repeated every
239 bytes on the wire. A live install accepted three blocks, failed block 4
with SW 6400, then 6985, and INSTALL [for install] answered 6A88. The same
slicing was inherited by the SCP81 helper from the SCP80 path, so
multi-block caps could not install there either; both are fixed.

Tests: blocks are consecutive and reassemble the C4 TLV byte-for-byte
(200 python); findings updated; service worker v149.

docs/scp81-findings.md

@@ -213,6 +213,22 @@ lengths are BER-encoded (`_ber_len_bytes`); the same rule as the BIP channel
 data TLV fix earlier the same day. Tests cover the 245-byte LOAD body, the
 short-form case and the definite variant.
 
+## RESOLVED 2026-09-16d: RAM install - LOAD blocks were overlapping copies
+
+**Root cause:** the LOAD block slicer indexed the load file TLV with the
+*block number* (`loadfile_tlv[i * 2:(i + 240) * 2] for i in range(blocks)`)
+instead of a *character offset*, so every block after the first was a
+1-byte-shifted copy of its predecessor. On the wire the cap header repeated
+every 239 bytes. The card accepted the first three blocks and failed block 4
+with `SW 6400` (execution error), then refused the rest (`6985`) and the
+final INSTALL answered `6A88`. The same slicing lived in the SCP80
+/api/ram-install path (the helper was extracted from it), so multi-block caps
+could never install there either.
+
+**Fix:** consecutive chunks at char offsets
+(`range(0, len(tlv), 240 * 2)`), with a reassembly test that pins the joined
+blocks to the C4 TLV byte for byte.
+
 ## Next tests / work
 
 1. **UI:** group the per-page R-APDUs under their logical command in the

frontend/index.html

@@ -18,7 +18,7 @@
 <div class="max-w-7xl mx-auto px-6 py-2">
 
 	<div class="flex items-center justify-between mb-3">
-		<h1 class="text-2xl font-bold text-heading">OTAMan <span id="slogan" class="text-sm font-normal text-gray-500 dark:text-slate-400 ml-2" data-l10n="SIM OTA with a Human Face">SIM OTA with a Human Face</span> <span class="text-xs text-gray-400 dark:text-slate-500 ml-1">v2.1.11</span></h1>
+		<h1 class="text-2xl font-bold text-heading">OTAMan <span id="slogan" class="text-sm font-normal text-gray-500 dark:text-slate-400 ml-2" data-l10n="SIM OTA with a Human Face">SIM OTA with a Human Face</span> <span class="text-xs text-gray-400 dark:text-slate-500 ml-1">v2.1.12</span></h1>
 		<div class="flex items-center gap-4">
 			<span id="state-indicator" class="flex items-center select-none" style="cursor:default" title="Connecting...">
 				<span id="state-indicator-dot" class="text-xs text-gray-400" title="Connecting...">●</span>

frontend/sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'otaman-v148';
+const CACHE = 'otaman-v149';
 const URLS = [
   'index.html',
   'help.html',

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "pysim-otaman-server"
-version = "2.1.11"
+version = "2.1.12"
 description = "HTTP REST server wrapping pysim for the OTAMan PWA"
 requires-python = ">=3.8"
 # pysim is a git-only dependency installed explicitly by setup.bat/setup.sh.

pysim_otaman_server/server.py

@@ -21,7 +21,7 @@ from osmocom.construct import GsmOrUcs2Adapter
 from osmocom.tlv import BER_TLV_IE
 
 
-VERSION = '2.1.11'
+VERSION = '2.1.12'
 
 MAX_ENVELOPE_SEGMENTS = 5  # max SMS segments for outgoing C-APDU in ENVELOPE
 
@@ -414,9 +414,12 @@ def _cap_apdu_sequence(loadfile_aid, module_aid, loadfile_data, sd_aid='',
     ifl_data = _lv(loadfile_aid) + _lv(sd) + '00' + '00' + '00'
     apdus = ['80E60200%02X%s00' % (len(ifl_data) // 2, ifl_data)]
     loadfile_tlv = 'C4' + _ber_len(len(loadfile_data) // 2) + loadfile_data
-    total_bytes = len(loadfile_tlv) // 2
-    blocks = [loadfile_tlv[i * 2:(i + block_size) * 2]
-              for i in range(0, (total_bytes + block_size - 1) // block_size)]
+    # Split the TLV into consecutive 240-byte blocks (char offsets, 2 per
+    # byte). The earlier form indexed with the block number ('i * 2'), which
+    # produced overlapping 1-byte-shifted copies - the card failed mid-load
+    # with SW 6400 (live 2026-09-16).
+    blocks = [loadfile_tlv[off:off + block_size * 2]
+              for off in range(0, len(loadfile_tlv), block_size * 2)]
     for i, block in enumerate(blocks):
         p1 = 0x80 if i == len(blocks) - 1 else 0x00
         apdus.append('80E8%02X%02X%02X%s00' % (p1, i % 256, len(block) // 2, block))

tests/test_ota_helpers.py

@@ -879,10 +879,20 @@ class CapApduSequenceTest(unittest.TestCase):
         self.assertIn('06A00000010001' + '05A000000100' + '05A000000100' + '0100', seq[2])
 
     def test_load_blocks_split_and_counter(self):
-        from pysim_otaman_server.server import _cap_apdu_sequence
-        data = 'AB' * 700          # 700 bytes -> C4 TLV 703 -> 3 x 240-byte blocks
+        from pysim_otaman_server.server import _cap_apdu_sequence, _ber_len as _ber_len_lower
+        data = ''.join('%02X' % (i % 256) for i in range(700))
         seq = _cap_apdu_sequence('A00000010001', 'A000000100', data)
         self.assertEqual(len(seq), 5)          # INSTALL + 3 LOAD + INSTALL
         self.assertEqual(seq[1][:8], '80E80000')
         self.assertEqual(seq[2][:8], '80E80001')
         self.assertEqual(seq[3][:8], '80E88002')   # last block: P1=0x80
+        # The blocks are consecutive chunks and reassemble the load file TLV
+        # byte-for-byte (a shifted/overlapping split fails the card mid-load).
+        def payload(apdu):
+            lc = int(apdu[8:10], 16)
+            return apdu[10:10 + lc * 2]
+        joined = payload(seq[1]) + payload(seq[2]) + payload(seq[3])
+        self.assertTrue(joined.startswith('C482'))
+        expected = 'C4' + _ber_len_lower(700) + data   # 700 = 0x2BC
+        self.assertEqual(joined.upper(), expected.upper())
+        self.assertEqual(int(seq[3][8:10], 16), len(expected) // 2 - 480)