feat: add XeSIM CTE and RedPocket VoWiFi compatibility

internal/vowifi/carrier_compat.go

@@ -0,0 +1,60 @@
+package vowifi
+
+import (
+	"fmt"
+	"strings"
+)
+
+const att310280EPDG = "epdg.epc.att.net"
+
+// AssignedRoutePLMN returns a narrowly matched ePDG route PLMN without
+// changing the subscription PLMN used for AKA identities. Some multi-profile
+// and MVNO SIMs authenticate against their own HPLMN but use a host network's
+// VoWiFi access gateway.
+func AssignedRoutePLMN(iccid, imsi string) (string, string, bool) {
+	iccid = strings.TrimSpace(iccid)
+	imsi = strings.TrimSpace(imsi)
+	switch {
+	case strings.HasPrefix(iccid, "894416") && strings.HasPrefix(imsi, "204047"):
+		// XeSIM/Lebara: keep 204/04 for AKA and use Vodafone UK's ePDG.
+		return "234", "15", true
+	case strings.HasPrefix(iccid, "894430") && strings.HasPrefix(imsi, "23433"):
+		// CTExcel UK: keep 234/33 for AKA and use the EE UK ePDG used by
+		// the initial VoWiFi provisioning path.
+		return "234", "30", true
+	default:
+		return "", "", false
+	}
+}
+
+// IsATT310280 reports whether the live subscription is on AT&T's three-digit
+// 310/280 PLMN. It is shared by SWu and IMS so the carrier exception cannot
+// drift between protocol layers.
+func IsATT310280(identity SIMIdentity) bool {
+	mcc := strings.TrimSpace(identity.HomeMCC)
+	mnc := strings.TrimLeft(strings.TrimSpace(identity.HomeMNC), "0")
+	imsi := strings.TrimSpace(identity.IMSI)
+	return mcc == "310" && mnc == "280" && strings.HasPrefix(imsi, "310280")
+}
+
+func applyAssignedCarrierRoute(identity SIMIdentity) SIMIdentity {
+	if strings.TrimSpace(identity.EPDG) != "" {
+		return identity
+	}
+	if routeMCC, routeMNC, ok := AssignedRoutePLMN(identity.ICCID, identity.IMSI); ok {
+		identity.EPDG = standardEPDGHostname(routeMCC, routeMNC)
+	}
+	return identity
+}
+
+func standardEPDGHostname(mcc, mnc string) string {
+	mnc = strings.TrimSpace(mnc)
+	for len(mnc) < 3 {
+		mnc = "0" + mnc
+	}
+	return fmt.Sprintf(
+		"epdg.epc.mnc%s.mcc%s.pub.3gppnetwork.org",
+		mnc,
+		strings.TrimSpace(mcc),
+	)
+}

internal/vowifi/carrier_compat_test.go

@@ -0,0 +1,56 @@
+package vowifi
+
+import "testing"
+
+func TestAssignedRoutePLMNUsesNarrowCardAndSubscriptionMatches(t *testing.T) {
+	tests := []struct {
+		name         string
+		iccid        string
+		imsi         string
+		wantMCC      string
+		wantMNC      string
+		wantAssigned bool
+	}{
+		{name: "XeSIM Lebara route", iccid: "89441600001001576265", imsi: "204047666157626", wantMCC: "234", wantMNC: "15", wantAssigned: true},
+		{name: "CTExcel initial route", iccid: "8944303773524055208", imsi: "234336570712415", wantMCC: "234", wantMNC: "30", wantAssigned: true},
+		{name: "XeSIM ICCID without matching subscription", iccid: "89441600001001576265", imsi: "204041666157626"},
+		{name: "similar ICCID must not match", iccid: "89441000001001576265", imsi: "204047666157626"},
+		{name: "generic EE SIM must not match CTExcel", iccid: "8944110000000000000", imsi: "234336570712415"},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			mcc, mnc, assigned := AssignedRoutePLMN(test.iccid, test.imsi)
+			if mcc != test.wantMCC || mnc != test.wantMNC || assigned != test.wantAssigned {
+				t.Fatalf("AssignedRoutePLMN() = %q/%q,%v, want %q/%q,%v", mcc, mnc, assigned, test.wantMCC, test.wantMNC, test.wantAssigned)
+			}
+		})
+	}
+}
+
+func TestApplyAssignedCarrierRoutePreservesAuthenticationPLMN(t *testing.T) {
+	identity := applyAssignedCarrierRoute(SIMIdentity{
+		ICCID: "8944303773524055208", IMSI: "234336570712415",
+		HomeMCC: "234", HomeMNC: "33",
+	})
+	if identity.HomeMCC != "234" || identity.HomeMNC != "33" {
+		t.Fatalf("authentication PLMN = %s/%s, want 234/33", identity.HomeMCC, identity.HomeMNC)
+	}
+	if identity.EPDG != "epdg.epc.mnc030.mcc234.pub.3gppnetwork.org" {
+		t.Fatalf("route ePDG = %q", identity.EPDG)
+	}
+}
+
+func TestIsATT310280RequiresMatchingPLMNAndIMSI(t *testing.T) {
+	if !IsATT310280(SIMIdentity{IMSI: "310280229187733", HomeMCC: "310", HomeMNC: "280"}) {
+		t.Fatal("AT&T 310/280 identity was not recognized")
+	}
+	for _, identity := range []SIMIdentity{
+		{IMSI: "310410229187733", HomeMCC: "310", HomeMNC: "280"},
+		{IMSI: "310280229187733", HomeMCC: "310", HomeMNC: "28"},
+		{IMSI: "310280229187733", HomeMCC: "311", HomeMNC: "280"},
+	} {
+		if IsATT310280(identity) {
+			t.Fatalf("unrelated identity matched AT&T 310/280: %#v", identity)
+		}
+	}
+}

internal/vowifi/ec20_adapter.go

@@ -97,9 +97,10 @@ type ec20RadioCheckpoint struct {
 }
 
 var (
-	_ SIMIdentityReader = (*EC20Adapter)(nil)
-	_ AKAProvider       = (*EC20Adapter)(nil)
-	_ RadioController   = (*EC20Adapter)(nil)
+	_ SIMIdentityReader    = (*EC20Adapter)(nil)
+	_ AKAProvider          = (*EC20Adapter)(nil)
+	_ PreferredAKAProvider = (*EC20Adapter)(nil)
+	_ RadioController      = (*EC20Adapter)(nil)
 )
 
 func NewEC20Adapter(
@@ -172,6 +173,7 @@ func (adapter *EC20Adapter) ReadIdentity(
 		HomeMCC: homeMCC,
 		HomeMNC: homeMNC,
 	}
+	identity = applyAssignedCarrierRoute(identity)
 	adapter.mu.Lock()
 	adapter.bindings[iccid] = ec20SIMBinding{
 		deviceID: deviceID,
@@ -208,6 +210,11 @@ func (adapter *EC20Adapter) readHomePLMN(
 	iccid string,
 	imsi string,
 ) (string, string, error) {
+	// AT&T 310/280 is a three-digit MNC. Prefer the assigned subscription
+	// prefix when EF_AD is stale or ambiguous after a profile switch.
+	if strings.HasPrefix(strings.TrimSpace(imsi), "310280") {
+		return "310", "280", nil
+	}
 	mncLength, efErr := adapter.readExplicitMNCLength(ctx, deviceID)
 	if efErr == nil {
 		if len(imsi) < 3+mncLength {
@@ -238,9 +245,10 @@ func assignedHomePLMN(imsi string) (mcc, mnc string, ok bool) {
 		prefix    string
 		mncLength int
 	}{
-		{prefix: "20404", mncLength: 2}, // Vodafone NL core; some Lebara subscriptions.
-		{prefix: "23415", mncLength: 2}, // Vodafone UK.
-		{prefix: "23487", mncLength: 2}, // Lebara Mobile UK.
+		{prefix: "20404", mncLength: 2},  // Vodafone NL core; some Lebara subscriptions.
+		{prefix: "23415", mncLength: 2},  // Vodafone UK.
+		{prefix: "23487", mncLength: 2},  // Lebara Mobile UK.
+		{prefix: "310280", mncLength: 3}, // AT&T / RedPocket GSMA.
 	}
 	for _, assignment := range assignments {
 		if strings.HasPrefix(imsi, assignment.prefix) {
@@ -391,11 +399,46 @@ func (adapter *EC20Adapter) Authenticate(
 	ctx context.Context,
 	identity SIMIdentity,
 	challenge AKAChallenge,
+) (AKAResult, error) {
+	return adapter.authenticateWithApplication(ctx, identity, challenge, "")
+}
+
+func (adapter *EC20Adapter) AuthenticateWithPreference(
+	ctx context.Context,
+	identity SIMIdentity,
+	challenge AKAChallenge,
+	preference string,
+) (AKAResult, error) {
+	return adapter.authenticateWithApplication(ctx, identity, challenge, preference)
+}
+
+func (adapter *EC20Adapter) authenticateWithApplication(
+	ctx context.Context,
+	identity SIMIdentity,
+	challenge AKAChallenge,
+	preference string,
 ) (AKAResult, error) {
 	binding, err := adapter.bindingFor(identity)
 	if err != nil {
 		return AKAResult{}, err
 	}
+	if strings.EqualFold(strings.TrimSpace(preference), "isim_strict") && binding.application != "ISIM" {
+		aid, application, err := adapter.discoverPreferredAKAApplication(
+			ctx,
+			binding.deviceID,
+			isimAIDPrefix,
+			"ISIM",
+		)
+		if err != nil {
+			return AKAResult{}, err
+		}
+		binding.aid = aid
+		binding.application = application
+		binding.basicChannel = false
+		adapter.mu.Lock()
+		adapter.bindings[binding.iccid] = binding
+		adapter.mu.Unlock()
+	}
 	if binding.aid == "" {
 		if _, err := adapter.CheckReady(ctx, identity); err != nil {
 			return AKAResult{}, err
@@ -405,6 +448,14 @@ func (adapter *EC20Adapter) Authenticate(
 			return AKAResult{}, err
 		}
 	}
+	if strings.EqualFold(strings.TrimSpace(preference), "isim_strict") && binding.application != "ISIM" {
+		return AKAResult{}, fmt.Errorf(
+			"%w: ISIM strict requested, selected %s (%s)",
+			ErrEC20ApplicationAbsent,
+			binding.application,
+			binding.aid,
+		)
+	}
 	if err := adapter.verifyLiveICCID(ctx, binding); err != nil {
 		return AKAResult{}, err
 	}
@@ -907,6 +958,28 @@ func (adapter *EC20Adapter) discoverAKAApplication(
 	return usimAIDPrefix, "USIM", nil
 }
 
+func (adapter *EC20Adapter) discoverPreferredAKAApplication(
+	ctx context.Context,
+	deviceID string,
+	aidPrefix string,
+	application string,
+) (string, string, error) {
+	response, err := adapter.execute(ctx, deviceID, "AT+CUAD")
+	if err == nil {
+		data, parseErr := parseCUADData(response)
+		if parseErr == nil {
+			for _, candidate := range collectApplicationAIDs(data) {
+				if strings.HasPrefix(candidate, aidPrefix) {
+					return candidate, application, nil
+				}
+			}
+		}
+	}
+	// AT+CUAD is optional. Returning the standard AID prefix still lets CCHO
+	// perform the authoritative application probe on older EC20 firmware.
+	return aidPrefix, application, nil
+}
+
 func (adapter *EC20Adapter) openLogicalChannel(
 	ctx context.Context,
 	deviceID string,
@@ -1146,12 +1219,27 @@ func parseCRSMData(response modem.Response) ([]byte, error) {
 }
 
 func parseCUADData(response modem.Response) ([]byte, error) {
-	fields := parseCSV(valueAfterATPrefix(response, "+CUAD:"))
-	if len(fields) == 0 {
+	// EC20 firmware may split the BER-TLV stream across adjacent quoted chunks
+	// and continuation lines. Concatenating every hex fragment prevents an ISIM
+	// AID after a USIM entry from being silently discarded.
+	var encoded strings.Builder
+	collect := false
+	for _, line := range response.Lines {
+		line = strings.TrimSpace(line)
+		if strings.HasPrefix(strings.ToUpper(line), "+CUAD:") {
+			collect = true
+			line = strings.TrimSpace(line[len("+CUAD:"):])
+		} else if !collect {
+			continue
+		}
+		for _, fragment := range quotedHexFragments(line) {
+			encoded.WriteString(fragment)
+		}
+	}
+	if encoded.Len() == 0 {
 		return nil, errors.New("CUAD response has no data")
 	}
-	value := fields[len(fields)-1]
-	data, err := hex.DecodeString(strings.Trim(value, `"`))
+	data, err := hex.DecodeString(encoded.String())
 	if err != nil || len(data) == 0 {
 		return nil, errors.New("CUAD response data is invalid")
 	}
@@ -1161,11 +1249,48 @@ func parseCUADData(response modem.Response) ([]byte, error) {
 	return data, nil
 }
 
+func quotedHexFragments(line string) []string {
+	var fragments []string
+	for {
+		start := strings.IndexByte(line, '"')
+		if start < 0 {
+			break
+		}
+		line = line[start+1:]
+		end := strings.IndexByte(line, '"')
+		if end < 0 {
+			break
+		}
+		fragment := strings.ToUpper(strings.TrimSpace(line[:end]))
+		line = line[end+1:]
+		if fragment == "" || len(fragment)%2 != 0 {
+			continue
+		}
+		valid := true
+		for _, character := range fragment {
+			if (character < '0' || character > '9') && (character < 'A' || character > 'F') {
+				valid = false
+				break
+			}
+		}
+		if valid {
+			fragments = append(fragments, fragment)
+		}
+	}
+	return fragments
+}
+
 func collectApplicationAIDs(data []byte) []string {
 	var result []string
 	var walk func([]byte)
 	walk = func(value []byte) {
 		for len(value) > 0 {
+			for len(value) > 0 && value[0] == 0xff {
+				value = value[1:]
+			}
+			if len(value) == 0 {
+				return
+			}
 			tag, constructed, body, consumed, err := decodeBERTLV(value)
 			if err != nil || consumed == 0 {
 				return

internal/vowifi/ec20_adapter_test.go

@@ -6,6 +6,7 @@ import (
 	"encoding/hex"
 	"errors"
 	"fmt"
+	"reflect"
 	"strings"
 	"sync"
 	"testing"
@@ -421,6 +422,7 @@ func TestAssignedHomePLMNIncludesLebaraUKCores(t *testing.T) {
 		"204040123456789": "204/04",
 		"234150123456789": "234/15",
 		"234870123456789": "234/87",
+		"310280229187733": "310/280",
 	}
 	for imsi, want := range tests {
 		mcc, mnc, ok := assignedHomePLMN(imsi)
@@ -430,6 +432,23 @@ func TestAssignedHomePLMNIncludesLebaraUKCores(t *testing.T) {
 	}
 }
 
+func TestEC20AdapterTreatsATT310280AsThreeDigitMNC(t *testing.T) {
+	t.Parallel()
+	transcript := &ec20Transcript{t: t, steps: identityTranscriptStepsWithoutEFAD("310280229187733")}
+	adapter, err := NewEC20Adapter(transcript, EC20AdapterOptions{})
+	if err != nil {
+		t.Fatal(err)
+	}
+	identity, err := adapter.ReadIdentity(context.Background(), "ec20-1")
+	if err != nil {
+		t.Fatalf("ReadIdentity: %v", err)
+	}
+	if identity.HomeMCC != "310" || identity.HomeMNC != "280" {
+		t.Fatalf("home PLMN = %s/%s, want 310/280", identity.HomeMCC, identity.HomeMNC)
+	}
+	transcript.assertDone()
+}
+
 func TestEC20AdapterRadioTransactionRestoresCFUNAndPDPContexts(
 	t *testing.T,
 ) {
@@ -598,3 +617,78 @@ func synchronizationFailureUSIMResponse() []byte {
 	raw = append(raw, auts...)
 	return append(raw, 0x90, 0x00)
 }
+
+func TestCollectApplicationAIDsSkipsCUADPadding(t *testing.T) {
+	t.Parallel()
+	response := modem.Response{Lines: []string{
+		`+CUAD: "61184F10A0000000871002FFFFFFFF890302000050045553494DFFFFFFFFFFFFFFFFFFFFFFFF""61184F10A0000000871004FFFFFFFF890302000050044953494DFFFFFFFFFFFFFFFFFFFFFFFF"`,
+		`"FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"`,
+	}}
+	data, err := parseCUADData(response)
+	if err != nil {
+		t.Fatal(err)
+	}
+	aids := collectApplicationAIDs(data)
+	want := []string{
+		"A0000000871002FFFFFFFF8903020000",
+		"A0000000871004FFFFFFFF8903020000",
+	}
+	if !reflect.DeepEqual(aids, want) {
+		t.Fatalf("AIDs = %v, want %v", aids, want)
+	}
+}
+
+func TestEC20AdapterISIMStrictUsesCUADFullAID(t *testing.T) {
+	var challenge AKAChallenge
+	for index := range challenge.RAND {
+		challenge.RAND[index] = byte(index)
+		challenge.AUTN[index] = byte(0xf0 + index)
+	}
+	authAPDU := buildUSIMAuthenticateAPDU(challenge)
+	authCommand := fmt.Sprintf(
+		`AT+CGLA=1,%d,"%s"`,
+		len(authAPDU)*2,
+		strings.ToUpper(hex.EncodeToString(authAPDU)),
+	)
+	encodedResponse := strings.ToUpper(hex.EncodeToString(successfulUSIMResponse()))
+	fullISIM := "A0000000871004FFFFFFFF8903020000"
+	cuad := `61184F10A0000000871002FFFFFFFF890302000050045553494D61184F10A0000000871004FFFFFFFF890302000050044953494D`
+	transcript := &ec20Transcript{
+		t: t,
+		steps: []ec20TranscriptStep{
+			{command: "AT+CPIN?", lines: []string{"+CPIN: READY"}},
+			{command: "AT+CIMI", lines: []string{"310280229187733"}},
+			{command: "AT+CCID", lines: []string{"+CCID: 89012804332291663965"}},
+			{command: "AT+CGSN", lines: []string{"863212060022487"}},
+			{command: "AT+CUAD", lines: []string{`+CUAD: "` + cuad + `"`}},
+			{command: "AT+CCID", lines: []string{"+CCID: 89012804332291663965"}},
+			{command: `AT+CCHO="` + fullISIM + `"`, lines: []string{"+CCHO: 1"}},
+			{
+				command:   authCommand,
+				sensitive: true,
+				lines: []string{fmt.Sprintf(
+					`+CGLA: %d,"%s"`,
+					len(encodedResponse),
+					encodedResponse,
+				)},
+			},
+			{command: "AT+CCHC=1"},
+		},
+	}
+	adapter, err := NewEC20Adapter(transcript, EC20AdapterOptions{})
+	if err != nil {
+		t.Fatal(err)
+	}
+	identity, err := adapter.ReadIdentity(context.Background(), "ec20-1")
+	if err != nil {
+		t.Fatalf("ReadIdentity: %v", err)
+	}
+	result, err := adapter.AuthenticateWithPreference(context.Background(), identity, challenge, "isim_strict")
+	if err != nil {
+		t.Fatalf("AuthenticateWithPreference: %v", err)
+	}
+	if !bytes.Equal(result.RES, []byte{1, 2, 3, 4, 5, 6, 7, 8}) {
+		t.Fatalf("RES = %x", result.RES)
+	}
+	transcript.assertDone()
+}

internal/vowifi/ims/digest.go

@@ -168,6 +168,7 @@ func authenticateAKA(
 	provider vowifi.AKAProvider,
 	identity vowifi.SIMIdentity,
 	challenge digestChallenge,
+	preference string,
 ) (akaMaterial, error) {
 	nonce, err := decodeAKANonce(challenge.Nonce)
 	if err != nil {
@@ -178,9 +179,18 @@ func authenticateAKA(
 	var akaChallenge vowifi.AKAChallenge
 	copy(akaChallenge.RAND[:], nonce[:16])
 	copy(akaChallenge.AUTN[:], nonce[16:32])
-	result, err := provider.Authenticate(ctx, identity, akaChallenge)
+	var result vowifi.AKAResult
+	if preferred, ok := provider.(vowifi.PreferredAKAProvider); ok && strings.TrimSpace(preference) != "" {
+		result, err = preferred.AuthenticateWithPreference(ctx, identity, akaChallenge, preference)
+	} else {
+		result, err = provider.Authenticate(ctx, identity, akaChallenge)
+	}
 	if err != nil {
-		return akaMaterial{}, fmt.Errorf("ims: USIM AKA authentication failed: %w", err)
+		application := "USIM"
+		if strings.EqualFold(strings.TrimSpace(preference), "isim_strict") {
+			application = "ISIM"
+		}
+		return akaMaterial{}, fmt.Errorf("ims: %s AKA authentication failed: %w", application, err)
 	}
 	if result.SynchronizationFailure || len(result.AUTS) > 0 {
 		if !result.SynchronizationFailure || len(result.AUTS) != 14 {

internal/vowifi/ims/digest_test.go

@@ -16,6 +16,21 @@ type recordingAKA struct {
 	challenges []vowifi.AKAChallenge
 }
 
+type recordingPreferredAKA struct {
+	recordingAKA
+	preference string
+}
+
+func (aka *recordingPreferredAKA) AuthenticateWithPreference(
+	ctx context.Context,
+	identity vowifi.SIMIdentity,
+	challenge vowifi.AKAChallenge,
+	preference string,
+) (vowifi.AKAResult, error) {
+	aka.preference = preference
+	return aka.Authenticate(ctx, identity, challenge)
+}
+
 func (aka *recordingAKA) CheckReady(context.Context, vowifi.SIMIdentity) (vowifi.AKAEvidence, error) {
 	return vowifi.AKAEvidence{Ready: true, Application: "usim"}, nil
 }
@@ -60,6 +75,7 @@ func TestAuthenticateAKAMapsNonceToTypedChallenge(t *testing.T) {
 		aka,
 		vowifi.SIMIdentity{IMSI: "001010123456789"},
 		digestChallenge{Nonce: base64.StdEncoding.EncodeToString(nonceBytes)},
+		"",
 	)
 	if err != nil {
 		t.Fatalf("authenticateAKA() error = %v", err)
@@ -93,6 +109,7 @@ func TestAuthenticateAKAReturnsSynchronizationEvidence(t *testing.T) {
 		aka,
 		vowifi.SIMIdentity{},
 		digestChallenge{Nonce: nonce},
+		"",
 	)
 	if err != nil {
 		t.Fatalf("authenticateAKA() error = %v", err)
@@ -102,6 +119,26 @@ func TestAuthenticateAKAReturnsSynchronizationEvidence(t *testing.T) {
 	}
 }
 
+func TestAuthenticateAKAUsesPreferredApplicationWhenSupported(t *testing.T) {
+	nonce := base64.StdEncoding.EncodeToString(make([]byte, 32))
+	aka := &recordingPreferredAKA{recordingAKA: recordingAKA{
+		result: vowifi.AKAResult{RES: []byte{1, 2, 3, 4}},
+	}}
+	_, err := authenticateAKA(
+		context.Background(),
+		aka,
+		vowifi.SIMIdentity{IMSI: "310280229187733"},
+		digestChallenge{Nonce: nonce},
+		"isim_strict",
+	)
+	if err != nil {
+		t.Fatalf("authenticateAKA() error = %v", err)
+	}
+	if aka.preference != "isim_strict" {
+		t.Fatalf("preference = %q, want isim_strict", aka.preference)
+	}
+}
+
 func TestBuildDigestAuthorizationCarriesAUTSWithEmptyResponse(t *testing.T) {
 	authorization := buildDigestAuthorization(
 		digestChallenge{

internal/vowifi/ims/provider.go

@@ -271,13 +271,22 @@ func deriveIdentities(identity vowifi.SIMIdentity, config Config) (identitySet,
 		mnc = "0" + mnc
 	}
 	domain := fmt.Sprintf("ims.mnc%s.mcc%s.3gppnetwork.org", mnc, mcc)
+	privateDomain := domain
+	publicDomain := domain
+	if vowifi.IsATT310280(identity) {
+		// AT&T provisions the IMPI and IMPU in its ISIM domains rather than
+		// the generic 3GPP PLMN IMS domain.
+		domain = "one.att.net"
+		privateDomain = "private.att.net"
+		publicDomain = "one.att.net"
+	}
 	privateIdentity := config.PrivateIdentity
 	if privateIdentity == "" {
-		privateIdentity = imsi + "@" + domain
+		privateIdentity = imsi + "@" + privateDomain
 	}
 	publicIdentity := config.PublicIdentity
 	if publicIdentity == "" {
-		publicIdentity = "sip:" + imsi + "@" + domain
+		publicIdentity = "sip:" + imsi + "@" + publicDomain
 	}
 	if strings.ContainsAny(privateIdentity+publicIdentity, "\r\n") ||
 		!strings.Contains(privateIdentity, "@") ||
@@ -536,6 +545,9 @@ func newSession(
 		}
 		protectedClientPort := provider.config.ProtectedClientPort
 		protectedServerPort := provider.config.ProtectedServerPort
+		if vowifi.IsATT310280(request.Identity) && protectedServerPort == 0 {
+			protectedServerPort = 6000
+		}
 		if securityEncryptionForIdentity(request.Identity) == "null" {
 			if protectedClientPort == 0 {
 				protectedClientPort = 5062
@@ -554,6 +566,10 @@ func newSession(
 			return nil, err
 		}
 		proposal.encryption = securityEncryptionForIdentity(request.Identity)
+		if vowifi.IsATT310280(request.Identity) {
+			proposal.integrityAlgorithms = []string{"hmac-sha-1-96"}
+			proposal.encryptionAlgorithmsList = []string{"aes-cbc"}
+		}
 		session.securityProposal = proposal
 		protectedTCP, err := net.ListenTCP(
 			"tcp",
@@ -732,7 +748,11 @@ func (session *Session) register(ctx context.Context, expires int) (*sipResponse
 		if err != nil {
 			return nil, err
 		}
-		material, err := authenticateAKA(ctx, session.provider.aka, session.request.Identity, challenge)
+		preference := ""
+		if vowifi.IsATT310280(session.request.Identity) {
+			preference = "isim_strict"
+		}
+		material, err := authenticateAKA(ctx, session.provider.aka, session.request.Identity, challenge, preference)
 		if err != nil {
 			return nil, err
 		}
@@ -792,6 +812,10 @@ func (session *Session) buildRegister(
 	authorizationHeader string,
 	authorization string,
 ) ([]byte, error) {
+	att310280 := vowifi.IsATT310280(session.request.Identity)
+	if att310280 {
+		expires = 18400
+	}
 	branch, err := randomHex(12)
 	if err != nil {
 		return nil, err
@@ -810,6 +834,17 @@ func (session *Session) buildRegister(
 		session.instanceID,
 		"urn%3Aurn-7%3A3gpp-service.ims.icsi.mmtel",
 	)
+	if att310280 {
+		contact = fmt.Sprintf(
+			`<sip:%s@%s;transport=%s>;+g.3gpp.accesstype="wlan1";audio;+g.3gpp.smsip;`+
+				`+g.3gpp.icsi-ref="%s";+sip.instance="<%s>"`,
+			session.identity.user,
+			contactAddress,
+			session.transport,
+			"urn%3Aurn-7%3A3gpp-service.ims.icsi.mmtel",
+			session.instanceID,
+		)
+	}
 	o2Germany := usesO2GermanyIMSProfile(session.request.Identity)
 	supported := "path, gruu"
 	allow := "REGISTER, INVITE, ACK, CANCEL, BYE, OPTIONS"
@@ -820,6 +855,13 @@ func (session *Session) buildRegister(
 		supported = "path, gruu, outbound, sec-agree, 100rel, timer"
 		allow = "INVITE, ACK, CANCEL, BYE, PRACK, UPDATE, INFO, MESSAGE, OPTIONS"
 	}
+	if att310280 {
+		supported = "path,sec-agree,gruu"
+	}
+	userAgent := strings.TrimSpace(session.provider.config.UserAgent)
+	if att310280 && (userAgent == "" || userAgent == "vocat/1") {
+		userAgent = "SimAdmin VoWiFi"
+	}
 	lines := []string{
 		"REGISTER " + requestURI + " SIP/2.0",
 		fmt.Sprintf("Via: SIP/2.0/%s %s;branch=z9hG4bK%s;rport", transportUpper, local, branch),
@@ -833,14 +875,23 @@ func (session *Session) buildRegister(
 		fmt.Sprintf("Expires: %d", expires),
 		"Supported: " + supported,
 		"Allow: " + allow,
-		"User-Agent: " + session.provider.config.UserAgent,
+		"User-Agent: " + userAgent,
 	}
 	if o2Germany {
 		lines = append(lines, "P-Preferred-Identity: <"+session.identity.public+">")
+	} else if att310280 {
+		lines = append(lines,
+			"P-Preferred-Identity: <"+session.identity.public+">",
+			`P-Visited-Network-ID: "one.att.net"`,
+			"P-Access-Network-Info: IEEE-802.11;i-wlan-node-id=000000000000;network-provided",
+			"Cellular-Network-Info: 3GPP-E-UTRAN-FDD;utran-cell-id-3gpp=3102800000000;cell-info-age=0",
+			"Accept-Contact: *;+g.3gpp.smsip",
+			`Accept-Contact: *;+g.3gpp.icsi-ref="urn%3Aurn-7%3A3gpp-service.ims.icsi.mmtel"`,
+		)
 	}
 	if session.securityOffered() {
 		lines = append(lines,
-			"Security-Client: "+session.securityProposal.headerValue(),
+			"Security-Client: "+session.securityClientValue(),
 			"Require: sec-agree",
 			"Proxy-Require: sec-agree",
 		)

internal/vowifi/ims/provider_test.go

@@ -442,6 +442,75 @@ func TestO2GermanyInitialRegisterMatchesSupportedIMSProfile(t *testing.T) {
 	}
 }
 
+func TestATT310280DeriveIdentitiesUsesISIMDomains(t *testing.T) {
+	identities, err := deriveIdentities(vowifi.SIMIdentity{
+		IMSI: "310280229187733", HomeMCC: "310", HomeMNC: "280",
+	}, Config{})
+	if err != nil {
+		t.Fatalf("deriveIdentities() error = %v", err)
+	}
+	if identities.domain != "one.att.net" ||
+		identities.private != "[email protected]" ||
+		identities.public != "sip:[email protected]" {
+		t.Fatalf("AT&T identities = %#v", identities)
+	}
+}
+
+func TestATT310280InitialRegisterMatchesProvisionedProfile(t *testing.T) {
+	client, server := net.Pipe()
+	defer client.Close()
+	defer server.Close()
+
+	identity := vowifi.SIMIdentity{
+		IMSI: "310280229187733", HomeMCC: "310", HomeMNC: "280",
+	}
+	identities, err := deriveIdentities(identity, Config{})
+	if err != nil {
+		t.Fatal(err)
+	}
+	session := &Session{
+		provider:   &Provider{config: Config{SecurityMode: SecurityRequired, UserAgent: "vocat/1"}},
+		request:    vowifi.IMSRequest{Identity: identity},
+		identity:   identities,
+		endpoint:   pcscfEndpoint{host: "pcscf.example", port: 5060},
+		transport:  "tcp",
+		conn:       client,
+		callID:     "att-test",
+		fromTag:    "tag",
+		instanceID: "urn:uuid:test",
+		securityProposal: securityProposal{
+			spiClient: 1546543, spiServer: 1546542,
+			portClient: 32773, portServer: 6000,
+			integrityAlgorithms:      []string{"hmac-sha-1-96"},
+			encryptionAlgorithmsList: []string{"aes-cbc"},
+		},
+	}
+	packet, err := session.buildRegister(1, 3600, "", "")
+	if err != nil {
+		t.Fatalf("buildRegister() error = %v", err)
+	}
+	request := string(packet)
+	for _, want := range []string{
+		"REGISTER sip:one.att.net SIP/2.0",
+		"Expires: 18400",
+		"Supported: path,sec-agree,gruu",
+		"User-Agent: SimAdmin VoWiFi",
+		`+g.3gpp.accesstype="wlan1";audio;+g.3gpp.smsip`,
+		"P-Preferred-Identity: <sip:[email protected]>",
+		`P-Visited-Network-ID: "one.att.net"`,
+		"P-Access-Network-Info: IEEE-802.11;i-wlan-node-id=000000000000;network-provided",
+		"Cellular-Network-Info: 3GPP-E-UTRAN-FDD;utran-cell-id-3gpp=3102800000000;cell-info-age=0",
+		"Accept-Contact: *;+g.3gpp.smsip",
+		"Security-Client: ipsec-3gpp; alg=hmac-sha-1-96; ealg=aes-cbc; prot=esp; mod=trans; spi-c=1546543; spi-s=1546542; port-c=32773; port-s=6000",
+		`username="[email protected]"`,
+		`uri="sip:one.att.net"`,
+	} {
+		if !strings.Contains(request, want) {
+			t.Fatalf("AT&T REGISTER omits %q:\n%s", want, request)
+		}
+	}
+}
+
 func serveRefreshFailure(listener *net.UDPConn, nonce string) error {
 	var callID string
 	for step := 0; step < 3; step++ {

internal/vowifi/ims/security.go

@@ -12,6 +12,8 @@ import (
 	"sort"
 	"strconv"
 	"strings"
+
+	"vocat/internal/vowifi"
 )
 
 type SecurityMode string
@@ -143,6 +145,19 @@ func (proposal securityProposal) headerValue() string {
 	return strings.Join(values, ", ")
 }
 
+func (session *Session) securityClientValue() string {
+	if vowifi.IsATT310280(session.request.Identity) {
+		return fmt.Sprintf(
+			"ipsec-3gpp; alg=hmac-sha-1-96; ealg=aes-cbc; prot=esp; mod=trans; spi-c=%d; spi-s=%d; port-c=%d; port-s=%d",
+			session.securityProposal.spiClient,
+			session.securityProposal.spiServer,
+			session.securityProposal.portClient,
+			session.securityProposal.portServer,
+		)
+	}
+	return session.securityProposal.headerValue()
+}
+
 func (proposal securityProposal) encryptionAlgorithm() string {
 	if strings.EqualFold(strings.TrimSpace(proposal.encryption), "null") {
 		return "null"

internal/vowifi/orchestrator.go

@@ -645,18 +645,13 @@ func DeriveEPDG(identity SIMIdentity) (string, error) {
 		}
 		return strings.ToLower(configured), nil
 	}
+	if IsATT310280(identity) {
+		return att310280EPDG, nil
+	}
 	if err := identity.validate(); err != nil {
 		return "", err
 	}
-	mnc := strings.TrimSpace(identity.HomeMNC)
-	for len(mnc) < 3 {
-		mnc = "0" + mnc
-	}
-	return fmt.Sprintf(
-		"epdg.epc.mnc%s.mcc%s.pub.3gppnetwork.org",
-		mnc,
-		strings.TrimSpace(identity.HomeMCC),
-	), nil
+	return standardEPDGHostname(identity.HomeMCC, identity.HomeMNC), nil
 }
 
 func normalizeProxyRoute(route ProxyRoute) (ProxyRoute, error) {

internal/vowifi/pcsc_adapter.go

@@ -53,18 +53,18 @@ func (adapter *PCSCAdapter) ReadIdentity(ctx context.Context, deviceID string) (
 	mncLength := identity.MNCLength
 	if mncLength != 2 && mncLength != 3 {
 		if mcc, mnc, ok := assignedHomePLMN(identity.IMSI); ok {
-			return SIMIdentity{ICCID: identity.ICCID, IMSI: identity.IMSI, HomeMCC: mcc, HomeMNC: mnc, SMSC: identity.SMSC}, nil
+			return applyAssignedCarrierRoute(SIMIdentity{ICCID: identity.ICCID, IMSI: identity.IMSI, HomeMCC: mcc, HomeMNC: mnc, SMSC: identity.SMSC}), nil
 		}
 		return SIMIdentity{}, ErrEC20MNCUnavailable
 	}
 	if len(identity.IMSI) < 3+mncLength {
 		return SIMIdentity{}, errors.New("vocat: USB SIM IMSI is shorter than its EF_AD home PLMN")
 	}
-	return SIMIdentity{
+	return applyAssignedCarrierRoute(SIMIdentity{
 		ICCID: identity.ICCID, IMSI: identity.IMSI,
 		HomeMCC: identity.IMSI[:3], HomeMNC: identity.IMSI[3 : 3+mncLength],
 		SMSC: identity.SMSC,
-	}, nil
+	}), nil
 }
 
 func (adapter *PCSCAdapter) ReadSMSCenter(ctx context.Context, deviceID string) (string, error) {

internal/vowifi/phone_test.go

@@ -125,6 +125,16 @@ func TestDeriveEPDGUsesExplicitPLMNAndNeverIMSIHeuristics(t *testing.T) {
 			},
 			want: "epdg.epc.mnc260.mcc310.pub.3gppnetwork.org",
 		},
+		{
+			name: "AT&T 310280 uses carrier endpoint",
+			identity: SIMIdentity{
+				ICCID:   "89012804332291663965",
+				IMSI:    "310280229187733",
+				HomeMCC: "310",
+				HomeMNC: "280",
+			},
+			want: "epdg.epc.att.net",
+		},
 		{
 			name: "explicit endpoint",
 			identity: SIMIdentity{

internal/vowifi/types.go

@@ -317,6 +317,14 @@ type AKAProvider interface {
 	Authenticate(context.Context, SIMIdentity, AKAChallenge) (AKAResult, error)
 }
 
+// PreferredAKAProvider optionally lets an AKA provider select a carrier-
+// provisioned application such as ISIM. Providers that only expose USIM keep
+// implementing AKAProvider unchanged.
+type PreferredAKAProvider interface {
+	AKAProvider
+	AuthenticateWithPreference(context.Context, SIMIdentity, AKAChallenge, string) (AKAResult, error)
+}
+
 // RadioController owns the host/modem radio projection. EnterVoWiFiRFOff must
 // not toggle the independent pure-airplane policy; Restore must return to the
 // captured pre-transaction state.