otaman/docs/scp81-findings.md

SCP81 / HTTP OTA live-card findings

Living debug log for the HTTP OTA (RAM over HTTP) work against the live UICC. Purpose: record every attempted configuration and its outcome, so the same variations are not repeated. Add rows as tests are run; keep the confirmed rules section current.

Setup: pysim_otaman_server with a PC/SC reader, the PWA SCP81 tab (or POST /api/scp81/bip), the card triggered by its SMS-PP push / the Location status event. Server log at GET /api/scp81/log, script state at GET /api/scp81/script, proactive history at GET /api/proactive-log.

RESOLVED 2026-09-16: the card never received the response - BIP TLV bug

Root cause: our RECEIVE DATA TERMINAL RESPONSE encoded the channel-data TLV length as a raw byte (36 ED ... for a 237-byte chunk). BER requires the long form for lengths >127: 36 81 ED ... (the reference terminal traces use exactly that, e.g. push_3311_success_req2.pcapng). The card's BIP layer silently mis-parsed the malformed TLV, so the TLS record bytes never reached its TLS stack: no alert, no script processing, and the SD kept resuming its dialog ("no complete script received") forever. Every delivery <=127 bytes (handshake records, 204 responses) always worked - which is why the handshake succeeded and only the large script responses "vanished".

Fix: _handle_bip_command (cmd 0x42) BER-encodes the channel data length (36 81 <len> above 127); regression test test_receive_data_tlv_long_form_length.

Result with the live card (one push, explore script, 5/5 commands):

#1 80CAFF2100        SW 9000  FF210B 81010D 8202C5D6 83020962   (13 applets,
                              free NV 50646 B, free volatile 2402 B)
#2 80F28002024F0000  SW 9000  ISD A000000003000000 + D276000005AAFFCAFE00
#3 80CA008500        SW 9000  stored HTTP OTA parameters
#4 80F24002024F0000  SW CAFE  127-byte ELF registry page (more available)
#5 80F21002024F0000  SW CAFE  127-byte applications page (more available)

Every command returned X-Admin-Script-Status: ok on the card's own POST to the incremented X-Admin-Next-URI, on the same keep-alive connection, and the session ended with 204 + mutual close_notify - exactly the reference flow. SW CAFE marks a truncated 127-byte page: the remaining entries need a continuation GET STATUS (P2=02 with the last AID as search criterion).

Live card facts (verified via the reader, 2026-09-16)

• 80CAFF2100 (GET DATA extended card resources) works: FF21 0B 81 01 0D 82 02 C5 D6 83 02 09 62 -> 13 applets installed, free NV memory 0xC5D6 = 50646 B, free volatile 0x0962 = 2402 B.
• 80CA008500 (GET DATA HTTP administration parameters) works and returns the SD's stored OTA configuration: 8A 09 "localhost", 8B 14 <agent id>, 8C 01 "/" (stored URI), 85 14 <PSK identity>, 86 07 00 01 25 03 00 10 00 (retry counter 1, timer 10 minutes), 02 40 01 (KVN/KID), APN-ish C7 04 03 47 50 42, destination BE 05 21 5B D5 05 02 = 91.213.5.2.
• 80F28002/80F24002/80F21002 ...4F0000 return 6985 through the reader when the ISD is not the current DF; the reference platform sends 80F28002024F0000 over HTTP, where the SD executes inside the ISD.
• SELECT of the ISD (00A4040008A000000003000000) returns 6112; a subsequent GET RESPONSE (00C0000012) returns 6D00.
• BIP device identities: OPEN CHANNEL uses destination 0x82; SEND/RECEIVE DATA carry channel 0x21..0x27 (e.g. 82 02 81 22 = channel 2).
• Subscribed events (99 03): 03 location status, 09 data available, 0A channel status.
• A Location status event re-triggers the OTA session only while the last session is incomplete; after a clean session end the card waits for a push.
• The SD stores a 10-minute retry timer (25 03 00 10 00).

Confirmed rules (with evidence)

1. The card needs a clean TLS close, with the close_notify actually fetched. Keep-alive (no close) -> fatal unexpected_message after it fetched the response. close_notify sent after the buffer drained is never fetched (the card ends the dialog on its own first). Correct order: send it while the response still waits, then wait for the drain, then close.
2. The card's abort alert is fatal unexpected_message - decrypted with the listener's keylog option (see tools/scp81_decrypt.py).
3. A dropped link must be signalled (TS 102 223 7.5.11), and only after the buffered data was fetched. Signalling the drop while bytes are still in the BIP buffer makes the card abort the fetch mid-record and end the session. Omitting the signal entirely hangs the SD: after a listener restart dropped the channel silently, the card ignored pushes and location events for minutes; a manual ENVELOPE (Channel status, B8 02 02 05) immediately made it start a fresh session.
4. The Next-URI shape matters. A path-only or absolute Next-URI (/, /1, http://127.0.0.1:8443/api/scp81) draws the fatal unexpected_message; the reference-style relative path with a query (/adminserver?PHPSESSID=...&apdu_id=101) does not.
5. The reference administration server (samples/HTTP_OTA/ httpota_adminserver_php_v2) uses: command script AE 80 22 <len> <apdu> 00 00; response 200 with X-Admin-Protocol, X-Admin-Next-URI: /adminserver?PHPSESSID=<id>&apdu_id=<n>, Content-Type: ...;version=1.0, chunked body (100-byte chunks); the card returns the R-APDU as the body of its next POST with X-Admin-Script-Status: ok; the server ends with 204. Its log proves the card followed the Next-URI three times within 1-2 s per step (Got next request ... Script status is 'ok' - storing R-APDU data).
6. chunked=false (Content-Length) has never produced an R-APDU. All sessions that ended silently (clean close, no alert, no POST) used Content-Length. Hypothesis: the card only treats a chunked body as a command script; with Content-Length it sees an empty script, executes nothing and ends the session gracefully.

The one fully successful session trace (ground truth)

traces/HTTPOTA_session_3311_success1.pcap (2019, plain HTTP on port 80, one TCP connection for the whole session, card 3311 - not our UICC):

POST /server/adminagent?cmd=1            <- card (trigger URI, with query!)
200 OK + Date/Server + X-Admin-Protocol
     + X-Admin-Next-URI: /Download?req=1 + Content-Length: 11
     + Content-Type: .../card-content-mgt;version=1.0
     body: ae 80 22 05 80 ca 00 85 00 00 00     (script: GET DATA 0085)
POST /Download?req=1                     <- card, SAME connection
  X-Admin-Script-Status: ok
  Content-Type: .../card-content-mgt-response;version=1.0
  Transfer-Encoding: chunked
  body: "8
" af 80 23 02 6a 88 00 00 "0

"   (R-APDU SW 6A88)
200 OK + X-Admin-Next-URI: /Download?req=2 + Content-Length: 14
     body: ae 80 22 08 80 f2 80 02 02 4f 00 00 00 00    (GET STATUS P1=80)
POST /Download?req=2  ->  X-Admin-Script-Status: ok, chunked
     body: "1F
" af 80 23 19 <25-byte R-APDU ... 90 00> 00 00 "0

"
200 OK + /Download?req=3 + 11-byte script
POST /Download?req=3  ->  status ok, R-APDU 23 02 6d 00 (SW 6D00)
204 No Content                          <- session ends

Confirmed from it: the card echoes the X-Admin-Next-URI (path and query) verbatim; its response POST goes on the same TCP connection; its response is the AF 80 23 <len> <R-APDU> 00 00 indefinite Response Scripting template (in a chunked body, with X-Admin-Script-Status); the server's script AE 80 22 <len> <APDU> 00 00 matches ours byte for byte; the server uses Content-Length (not chunked), no Connection header (implicit keep-alive), and ends with 204.

Attempt matrix

#	transport	framing	Next-URI	close	link events	outcome
1	dump mode only	-	-	-	off	OPEN CHANNEL + ClientHello captured (Phase A)
2	TLS, 204 only	-	-	yes	off	session completes cleanly, no alert (Phase B, live)
3	TLS + script	chunked 100	/N	early (raced fetch)	on	fetch truncated (237/399); card re-opened and repeated its POST with X-Admin-Resume: true -> breakdown-resume works
4	TLS + script	chunked 100 / single	/1, /, absolute	keep-alive	off	full fetch, then fatal unexpected_message (Next-URI shape)
5	TLS + script	single	none ("")	keep-alive	off	no alert, no POST, session left open (spec: no Next-URI -> no response)
6	TLS + script	chunked 100	reference	close_notify after drain	off	full fetch, alert (notify never fetched)
7	TLS + script	chunked 100	reference	close_notify before drain	off	full fetch, alert (head split into its own record)
8	TLS + script	single record	reference	drain + close_notify	off	no alert, card CLOSE CHANNELs, no R-APDU (chunked=false -> suspected empty script)
9	TLS + script	single record	reference	keep-alive (no close)	off	fatal unexpected_message (close required)
10	TLS + script	chunked 100	reference	drain + close_notify	off	full fetch, then alert; later the SD hung until a manual link-dropped event
11	TLS + script	single record	reference	keep-alive	off	fatal unexpected_message after the full fetch (no close)
12	TLS + script	single record	reference	drain + close_notify	off	no alert, card CLOSE CHANNELs, no R-APDU (Content-Length)
13	TLS + script	chunked100 + single	reference	drain + close_notify	off	no alert, no R-APDU
14	TLS + script	single record	reference	keep-alive	off	alert again
15	TLS + script	chunked 100	reference	keep-alive	on	alert (small records, ruled out record size)
16	TLS + script	single record	reference	keep-alive, no Connection header	on	alert
17	TLS + script (RFM! 00D6 write-probe)	chunked, single	reference	drain + close_notify	on	no alert, no R-APDU; EF.SPN unchanged - RFM result is void: the ISD only accepts RAM commands

All script attempts used the explore list, except #8-#17 which used only 80CAFF2100 (or the RFM probe). #3-#17 ran with the card's PSK identity 89390…903 (push trigger) or 89701… (event trigger).

Status after #17 (superseded by the 2026-09-16 resolution above): the failures were caused by the BIP TLV length bug, not by the HTTP/TLS details; resume mode was a symptom (the working session even started as a resume). The key working recipe (also now the server default): one keep-alive connection, Apache-style headers, Transfer-Encoding: chunked body with the script in one TLS record, no Connection header, X-Admin-Next-URI with a query whose command id increments.

Also confirmed: a TLS half-close (close_notify then keep reading for the card's POST which RFC 5246 leaves open in practice) cannot be done with CPython's ssl: SSLSocket.unwrap() with a short timeout raises and poisons the session (tested), so the half_close option is a documented no-op.

RESOLVED 2026-09-16b: SW CAFE continuation pages

Implemented: the script responder auto-follows a truncated listing page (SW CAFE, 127 bytes) by inserting a continuation GET STATUS (80F2 <P1> 02 <Lc> 4F <len> <last-complete-AID> 00, next-occurrence mode) as the next command. The last AID comes from the last complete E3 entry in the page (truncated tails and the live FC-prefixed junk are skipped). Logged as script-page; a repeated page logs script-page-stalled and stops; max 24 pages; inserted continuations are dropped at session start.

Live-verified (2026-09-16): ELF registry: page 1 SW CAFE -> continuation with D276000005AA060200000000B00000 -> page 2 SW 9000 (complete, 2 entries). Applications: page 1 SW CAFE -> continuation with D276000005AAFFCAFE0010 -> page 2 SW 9000 (complete, incl. D276000005AAFFCAFE0001/0010, A0000001515350, A000000151535041). Full session: 7/7 commands, all X-Admin-Script-Status: ok.

RESOLVED 2026-09-16c: RAM install over SCP81 - BER length in the script template

Root cause: _scp81_command_body wrote the C-APDU TLV length as a raw byte (AE 80 22 F5 <245 bytes> 00 00 for a 245-byte LOAD). BER reads a byte above 0x7F as a long-form marker, so the card mis-parsed every LOAD >128 bytes; the small INSTALL commands (<128 bytes) executed normally, which made the install look alive. Symptoms: the card accepted the LOAD responses with X-Admin-Script-Status: ok but sent a degenerate AF 80 body, no LOAD R-APDU appeared in the results, and the final INSTALL [for install] answered 6A88 (module not found) because the package was never loaded.

Fix: both the indefinite ("22" TLV) and definite ("AA" outer) template 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.

Next tests / work

1. UI: group the per-page R-APDUs under their logical command in the SCP81 tab (page merging/decoding for ELF and application listings); expose the framing options in the tab.
2. Load/store over SCP81: implemented - POST /api/scp81/ram-install takes a .cap, expands it with the shared _cap_apdu_sequence helper (INSTALL [for load] -> 240-byte LOAD blocks -> INSTALL [for install]) and queues it as the command script, one C-APDU per POST. Live install test pending (needs a push with a suitable applet).

Tooling

• tools/scp81_decrypt.py <log.json> <keys.log> - decrypts the dialog from GET /api/scp81/log plus the listener's keylog file (SSLKEYLOGFILE format; PSK-AES128-CBC-SHA256, TLS 1.2 PRF + OpenSSL CLI). Shows each record's plaintext and any alert level/description.
• Start the listener with "keylog": "/tmp/.../scp81.keys" to collect the secrets (contains key material - use a temp path, never commit).