SAIP: add PE-USIM with EF.IMSI + full-sequence decoder

The SAIP profile now personalizes EF.IMSI via a PE-USIM referencing the standard
"created by default" USIM template (OID 2.23.143.1.2.4), so the package carries
ICCID + IMSI + Ki/OPc. IMSI content uses the existing TS 31.102 enc_imsi.

Add decode_saip_profile(): splits the concatenated ProfileElements by DER TLV
boundaries and decodes each (asn1tools decodes only one value at a time).

Tests: full-sequence decode ([header, usim, akaParameter, end]) and IMSI-in-USIM
round-trip; 93 pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CHANGELOG.md

@@ -9,13 +9,17 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 - **Real SGP.22 SAIP profile generation** (`profile.format: saip`).
-  `server/saip_profile.py` encodes a DER `ProfileElement` sequence (ProfileHeader
-  with ICCID + Milenage AKA parameters carrying Ki/OPc) with `asn1tools` against
-  the official `PE_Definitions` ASN.1 schema — no pySim Python imports (the schema
-  is located from an installed pySim, or via `SAIP_ASN_PATH`). Self-contained and
-  optional: `saip_available()` gates it and the app falls back to `profile-v2`
-  when prerequisites are missing. Optional deps in `requirements-saip.txt`.
-  IMSI/other EFs (USIM-template PEs) are the documented next layer.
+  `server/saip_profile.py` encodes a DER `ProfileElement` sequence — ProfileHeader
+  (ICCID), PE-USIM personalizing EF.IMSI against the standard USIM template
+  (`2.23.143.1.2.4`), and Milenage AKA parameters (Ki/OPc) — with `asn1tools`
+  against the official `PE_Definitions` ASN.1 schema. No pySim Python imports (the
+  schema is located from an installed pySim, or via `SAIP_ASN_PATH`), so it avoids
+  the pyscard/smpp card-reader stack; the only runtime dep is `asn1tools`.
+  Self-contained and optional: `saip_available()` gates it and the app falls back
+  to `profile-package-v2` when prerequisites are missing. `decode_saip_profile()`
+  parses a package back into its ProfileElements. Optional deps in
+  `requirements-saip.txt`. A fully installable profile (remaining mandatory PEs +
+  card validation) is the documented next layer.
 - `pytest.ini` to silence asn1tools/pyparsing deprecation warnings.
 
 ### Security

README.md

@@ -102,16 +102,18 @@ Two formats are selectable via `profile.format`:
   the raw credentials plus **real 3GPP field encodings** (`EF_ICCID`, `EF_IMSI`,
   nibble-swapped BCD per 3GPP TS 31.102) and an SGP.22 **LPA activation code**
   (`LPA:1$<smdp>$<matching-id>`).
-- **`saip`** — a real DER-encoded **SGP.22 SAIP `ProfileElement` sequence**
-  (ProfileHeader with ICCID + Milenage AKA parameters carrying Ki/OPc), built
-  with `asn1tools` against the official `PE_Definitions` ASN.1 schema. Enable by
-  installing `requirements-saip.txt` (see that file for the schema source) and
-  setting `profile.format: saip`. If prerequisites are missing the server logs a
-  warning and falls back to `v2`.
+- **`saip`** — a real DER-encoded **SGP.22 SAIP `ProfileElement` sequence**:
+  ProfileHeader (ICCID), PE-USIM personalizing EF.IMSI against the standard USIM
+  template, and Milenage AKA parameters (Ki/OPc). Built with `asn1tools` against
+  the official `PE_Definitions` ASN.1 schema. Enable by installing
+  `requirements-saip.txt` (see that file for the schema source) and setting
+  `profile.format: saip`. If prerequisites are missing the server logs a warning
+  and falls back to `v2`. `saip_profile.decode_saip_profile()` parses a package
+  back into its ProfileElements for inspection.
 
-The SAIP package currently carries ICCID and the AKA credentials; emitting IMSI
-and other EFs (USIM-template / GenericFileManagement PEs with File Control
-Parameters) is the next layer. Note that consumer over-the-air install still
+The SAIP package carries ICCID, IMSI, and the AKA credentials; a fully
+installable profile additionally needs the remaining mandatory PEs (MF, PIN/PUK,
+full EF set) and card-level validation. Consumer over-the-air install also
 requires an SM-DP+ / LPA; these packages target programmable SIMs and
 core-network sync. See [`CHANGELOG.md`](CHANGELOG.md).
 

server/saip_profile.py

@@ -26,6 +26,11 @@ logger = logging.getLogger(__name__)
 
 _ASN_RELPATH = os.path.join("esim", "asn1", "saip", "PE_Definitions-3.3.1.asn")
 
+# Standard "created by default" USIM ADF template (TCA eUICC prefix 2.23.143.1
+# + templates.2 + usim.4). The eUICC creates ADF.USIM and its default EFs from
+# this template; the profile only personalizes the EFs it fills (here EF.IMSI).
+USIM_TEMPLATE_OID = "2.23.143.1.2.4"
+
 
 def find_saip_asn() -> Optional[str]:
     """Locate the SAIP ASN.1 schema: SAIP_ASN_PATH override, else pySim's copy."""
@@ -74,10 +79,10 @@ def create_saip_profile(
     profile_name: str = "",
     carrier_name: str = "",
 ) -> bytes:
-    """Build a DER-encoded SAIP ProfileElement sequence (header + AKA + end).
+    """Build a DER-encoded SAIP ProfileElement sequence.
 
-    ``imsi`` is accepted for signature parity with ``create_esim_profile`` and is
-    reserved for the forthcoming USIM/EF layer; it is not yet encoded into an EF.
+    Emits: ProfileHeader (with ICCID), PE-USIM (personalizing EF.IMSI against the
+    standard USIM template), Milenage PE-AKAParameter (Ki/OPc), and PE-End.
     """
     asn = _compiler()
     if asn is None:
@@ -87,7 +92,7 @@ def create_saip_profile(
         )
 
     # Imported here to avoid a hard dependency cycle at module import time.
-    from server.profile_generator import enc_iccid
+    from server.profile_generator import enc_iccid, enc_imsi
 
     ki_bytes = ki if isinstance(ki, bytes) else bytes.fromhex(ki)
     opc_bytes = opc if isinstance(opc, bytes) else bytes.fromhex(opc)
@@ -100,8 +105,17 @@ def create_saip_profile(
         "eUICC-Mandatory-services": {"usim": None, "milenage": None},
         "eUICC-Mandatory-GFSTEList": [],
     })
+    usim = ("usim", {
+        "usim-header": {"identification": 1},
+        "templateID": USIM_TEMPLATE_OID,
+        "adf-usim": [],
+        "ef-imsi": [("fillFileContent", enc_imsi(imsi))],
+        # Other mandatory files are left to the template (empty = no override).
+        "ef-arr": [], "ef-ust": [], "ef-spn": [], "ef-est": [],
+        "ef-acc": [], "ef-ecc": [],
+    })
     aka = ("akaParameter", {
-        "aka-header": {"identification": 1},
+        "aka-header": {"identification": 2},
         "algoConfiguration": ("algoParameter", {
             "algorithmID": 1,            # Milenage
             "algorithmOptions": b"\x00",
@@ -109,7 +123,42 @@ def create_saip_profile(
             "opc": opc_bytes,
         }),
     })
-    end = ("end", {"end-header": {"identification": 2}})
+    end = ("end", {"end-header": {"identification": 3}})
 
     logger.debug(f"Encoding SAIP profile for IMSI {imsi} (ICCID {iccid})")
-    return b"".join(asn.encode("ProfileElement", pe) for pe in (header, aka, end))
+    return b"".join(asn.encode("ProfileElement", pe) for pe in (header, usim, aka, end))
+
+
+def _split_der(data: bytes):
+    """Yield byte-range slices of consecutive top-level DER TLVs in ``data``."""
+    i, n = 0, len(data)
+    while i < n:
+        start = i
+        first = data[i]
+        i += 1
+        if first & 0x1F == 0x1F:  # high-tag-number form: skip continuation octets
+            while i < n and data[i] & 0x80:
+                i += 1
+            i += 1
+        length_byte = data[i]
+        i += 1
+        if length_byte & 0x80:  # long-form length
+            num = length_byte & 0x7F
+            length = int.from_bytes(data[i:i + num], "big")
+            i += num
+        else:
+            length = length_byte
+        i += length
+        yield data[start:i]
+
+
+def decode_saip_profile(data: bytes) -> list:
+    """Decode a SAIP ProfileElement sequence into a list of (choice, value).
+
+    asn1tools decodes a single value, so we split the concatenated PEs by their
+    DER TLV boundaries and decode each one.
+    """
+    asn = _compiler()
+    if asn is None:
+        raise RuntimeError("SAIP decoding unavailable (asn1tools/schema missing)")
+    return [asn.decode("ProfileElement", pe) for pe in _split_der(data)]

tests/test_saip.py

@@ -2,7 +2,9 @@ import pytest
 import yaml
 
 from server.app import create_app
-from server.profile_generator import derive_opc, enc_iccid, generate_iccid, generate_ki
+from server.profile_generator import (
+    derive_opc, enc_iccid, enc_imsi, generate_iccid, generate_ki,
+)
 import server.saip_profile as saip
 
 _OP = bytes.fromhex("63bfa50ee6523365ff14c1f45f88737d")
@@ -50,16 +52,24 @@ class TestSaipEncoding:
         assert pkg[0] == 0xA0
 
     @saip_required
-    def test_header_roundtrips_iccid(self):
+    def test_full_sequence_decodes(self):
         ki = generate_ki()
         opc = derive_opc(ki, _OP)
         iccid = generate_iccid()
         pkg = saip.create_saip_profile("302720000000001", ki, opc, iccid, "P", "C")
-        asn = saip._compiler()
-        choice, value = asn.decode("ProfileElement", pkg)
-        assert choice == "header"
-        assert value["iccid"] == enc_iccid(iccid)
-        assert value["major-version"] == 3
+        pes = saip.decode_saip_profile(pkg)
+        assert [choice for choice, _ in pes] == ["header", "usim", "akaParameter", "end"]
+        header = dict(pes)["header"]
+        assert header["iccid"] == enc_iccid(iccid)
+        assert header["major-version"] == 3
+
+    @saip_required
+    def test_imsi_embedded_in_usim(self):
+        imsi = "302720123456789"
+        pkg = saip.create_saip_profile(imsi, generate_ki(), b"\x11" * 16, generate_iccid())
+        usim = dict(saip.decode_saip_profile(pkg))["usim"]
+        assert usim["templateID"] == saip.USIM_TEMPLATE_OID
+        assert usim["ef-imsi"] == [("fillFileContent", enc_imsi(imsi))]
 
     @saip_required
     def test_credentials_embedded(self):