split cert and key location and allow key lookup on tpm

client/internal/certproof/README.md

@@ -16,7 +16,7 @@ to one WireGuard peer key and cannot be replayed by another peer.
 | macOS | console user's login keychain | a helper in that user's desktop session |
 | Windows | `LocalMachine\MY` | the service, directly |
 | Windows | signed-in user's `CurrentUser\MY` | a helper launched with that session's token |
-| Linux and others | PEM directory, `NB_CERT_STORE_DIR` or `/etc/netbird/certs` | the daemon, directly |
+| Linux and others | PEM directory: `CertStoreDir` in the profile config, else `NB_CERT_STORE_DIR`, else `/etc/netbird/certs` | the daemon, directly |
 | Linux | a `TSS2 PRIVATE KEY` file in that directory, signed by the TPM | the daemon, through `/dev/tpmrm0` |
 | Linux | a PKCS#11 token, tpm2-pkcs11 for one, enabled by `CertPKCS11PIN` in the profile config | the daemon, through the token's module, in builds with the `pkcs11` tag |
 
@@ -170,9 +170,17 @@ or `pin-source` naming a file, and `CertPKCS11PIN` takes precedence over both. W
 PIN no login happens, and tpm2-pkcs11 then shows no private keys at all. Every other
 attribute is ignored.
 
-Certificates and private keys are paired by `CKA_ID`, which is what `tpm2_ptool addcert`
-and `pkcs11-tool` set. Chains are completed from the other certificates on the token. Each
-operation opens a session, logs in, works, logs out and closes, so no token handle
+The certificate may live on the token or in the PEM directory: `CertStoreDir` in the
+profile config, else `NB_CERT_STORE_DIR`, else `/etc/netbird/certs`. On the token,
+certificates and private keys are paired by `CKA_ID`,
+which is what `tpm2_ptool addcert` and `pkcs11-tool` set. In the directory, a certificate
+file without a key of its own is paired with the token key whose public key it carries, so
+`device.pem` alone next to a key that only the TPM holds is enough; the token's public key
+object, which `tpm2_ptool addkey` and `import` create alongside the private one, is what
+the store compares against. Chains are completed from the certificates on the token and in
+the directory together, so intermediates may sit in either place.
+
+Each operation opens a session, logs in, works, logs out and closes, so no token handle
 outlives a call, and the PEM directory keeps working when the token does not: the two are
 queried together and a failing token is logged rather than hiding file certificates.
 

client/internal/certproof/collect_darwin.go

@@ -24,7 +24,7 @@ const helperTimeout = 30 * time.Second
 // installs device identities, and reaches the console user's login keychain only by
 // launching a helper into that user's session. A Mac sitting at the login window
 // therefore yields device proofs alone.
-func CollectProofs(ctx context.Context, checks []*proto.Checks, peerKey []byte, _ PKCS11Config) []certposture.Proof {
+func CollectProofs(ctx context.Context, checks []*proto.Checks, peerKey []byte, _ Config) []certposture.Proof {
 	challenges := certificateChallenges(checks)
 	if len(challenges) == 0 {
 		logNoChallenges(checks)

client/internal/certproof/collect_other.go

@@ -9,12 +9,12 @@ import (
 	"github.com/netbirdio/netbird/shared/management/proto"
 )
 
-// CollectProofs answers the certificate challenges in checks from the platform store,
-// joined by the PKCS#11 token that token names when it names one. Only macOS and
-// Windows keep per-user certificates out of reach of a privileged daemon, so every
-// other platform reads its store in the daemon itself.
-func CollectProofs(ctx context.Context, checks []*proto.Checks, peerKey []byte, token PKCS11Config) []certposture.Proof {
-	return Collect(ctx, storeWithToken(token), checks, peerKey)
+// CollectProofs answers the certificate challenges in checks from the PEM directory cfg
+// names, joined by its PKCS#11 token when it names one. Only macOS and Windows keep
+// per-user certificates out of reach of a privileged daemon, so every other platform
+// reads its store in the daemon itself.
+func CollectProofs(ctx context.Context, checks []*proto.Checks, peerKey []byte, cfg Config) []certposture.Proof {
+	return Collect(ctx, storeWithToken(cfg), checks, peerKey)
 }
 
 // helperStore is the store the helper reads. Nothing launches a helper on these

client/internal/certproof/collect_windows.go

@@ -25,7 +25,7 @@ const helperTimeout = 30 * time.Second
 // Intune enrol device certificates, and reaches the signed-in user's store by launching
 // a helper with that session's token. A machine at the sign-in screen therefore proves
 // device certificates alone.
-func CollectProofs(ctx context.Context, checks []*proto.Checks, peerKey []byte, _ PKCS11Config) []certposture.Proof {
+func CollectProofs(ctx context.Context, checks []*proto.Checks, peerKey []byte, _ Config) []certposture.Proof {
 	challenges := certificateChallenges(checks)
 	if len(challenges) == 0 {
 		logNoChallenges(checks)

client/internal/certproof/pkcs11store.go

@@ -23,23 +23,28 @@ type PKCS11Config struct {
 }
 
 // PKCS11Store yields the identities of a PKCS#11 token, which is how tpm2-pkcs11 exposes
-// TPM-held keys on Linux. Certificates and keys are paired by CKA_ID, the convention
-// tpm2_ptool addcert and pkcs11-tool follow, and every signature happens on the token.
+// TPM-held keys on Linux. Certificates on the token are paired with keys by CKA_ID, the
+// convention tpm2_ptool addcert and pkcs11-tool follow; certificate files in the PEM
+// directory by public key. Every signature happens on the token.
 type PKCS11Store struct {
-	uri *pkcs11.URI
-	pin string
+	uri     *pkcs11.URI
+	pin     string
+	certDir string
 }
 
-// NewPKCS11Store parses cfg.URI, standing in the bare defaults when it is empty.
-func NewPKCS11Store(cfg PKCS11Config) (*PKCS11Store, error) {
+// NewPKCS11Store parses cfg.URI, standing in the bare defaults when it is empty. Files in
+// certDir without a key of their own are paired with the token's keys by public key.
+func NewPKCS11Store(cfg PKCS11Config, certDir string) (*PKCS11Store, error) {
+	store := &PKCS11Store{uri: &pkcs11.URI{}, pin: cfg.PIN, certDir: certDir}
 	if cfg.URI == "" {
-		return &PKCS11Store{uri: &pkcs11.URI{}, pin: cfg.PIN}, nil
+		return store, nil
 	}
 	parsed, err := pkcs11.ParseURI(cfg.URI)
 	if err != nil {
 		return nil, err
 	}
-	return &PKCS11Store{uri: parsed, pin: cfg.PIN}, nil
+	store.uri = parsed
+	return store, nil
 }
 
 func (s *PKCS11Store) Candidates(_ context.Context) ([]Candidate, error) {
@@ -53,25 +58,115 @@ func (s *PKCS11Store) Candidates(_ context.Context) ([]Candidate, error) {
 	if err != nil {
 		return nil, err
 	}
-	log.Infof("%s holds %d certificates", s, len(certs))
+	fileChains, err := s.fileChains()
+	if err != nil {
+		return nil, err
+	}
+	log.Infof("%s holds %d certificates, %d certificate files without a key wait for its keys", s, len(certs), len(fileChains))
 
 	pool := make([]*x509.Certificate, 0, len(certs))
 	for _, cert := range certs {
 		pool = append(pool, cert.cert)
 	}
+	for _, chain := range fileChains {
+		pool = append(pool, chain...)
+	}
+
 	var candidates []Candidate
 	for _, cert := range certs {
 		if _, err := privateKey(session, cert.id); err != nil {
 			log.Infof("%s certificate %q has no usable private key: %v", s, cert.cert.Subject, err)
 			continue
 		}
-		chain := buildChain(cert.cert, pool)
-		log.Infof("%s candidate %q issued by %q built a chain of %d certificates", s, cert.cert.Subject, cert.cert.Issuer, len(chain))
-		candidates = append(candidates, Candidate{Chain: chain, Signer: &pkcs11Signer{store: s, leaf: cert.cert, id: cert.id}})
+		candidates = append(candidates, s.candidate(cert.cert, cert.id, pool))
+	}
+	if len(fileChains) == 0 {
+		return candidates, nil
+	}
+
+	keys, err := tokenPublicKeys(session)
+	if err != nil {
+		return nil, err
+	}
+	for _, chain := range fileChains {
+		leaf := chain[0]
+		id, ok := keys.idFor(leaf.PublicKey)
+		if !ok {
+			log.Debugf("%s holds no key for certificate %q from %s", s, leaf.Subject, s.certDir)
+			continue
+		}
+		candidates = append(candidates, s.candidate(leaf, id, pool))
 	}
 	return candidates, nil
 }
 
+func (s *PKCS11Store) candidate(leaf *x509.Certificate, id []byte, pool []*x509.Certificate) Candidate {
+	chain := buildChain(leaf, pool)
+	log.Infof("%s candidate %q issued by %q built a chain of %d certificates", s, leaf.Subject, leaf.Issuer, len(chain))
+	return Candidate{Chain: chain, Signer: &pkcs11Signer{store: s, leaf: leaf, id: id}}
+}
+
+// fileChains reads the certificate files in the PEM directory that carry no key of their
+// own; the file store answers for the ones that do.
+func (s *PKCS11Store) fileChains() ([][]*x509.Certificate, error) {
+	if s.certDir == "" {
+		return nil, nil
+	}
+	paths, err := certFiles(s.certDir)
+	if err != nil {
+		return nil, err
+	}
+	var chains [][]*x509.Certificate
+	for _, path := range paths {
+		chain, signer, err := loadPEM(path)
+		if err != nil || signer != nil {
+			continue
+		}
+		chains = append(chains, chain)
+	}
+	return chains, nil
+}
+
+type tokenKey struct {
+	id     []byte
+	public crypto.PublicKey
+}
+
+type tokenKeys []tokenKey
+
+func tokenPublicKeys(session *pkcs11.Session) (tokenKeys, error) {
+	objects, err := session.FindObjects(pkcs11.Attribute{Type: pkcs11.AttrClass, Value: pkcs11.ULong(pkcs11.ClassPublicKey)})
+	if err != nil {
+		return nil, err
+	}
+	keys := make(tokenKeys, 0, len(objects))
+	for _, object := range objects {
+		id, err := session.Attribute(object, pkcs11.AttrID)
+		if err != nil {
+			return nil, err
+		}
+		public, err := session.PublicKey(object)
+		if err != nil {
+			log.Debugf("skipping public key on PKCS#11 token: %v", err)
+			continue
+		}
+		keys = append(keys, tokenKey{id: id, public: public})
+	}
+	return keys, nil
+}
+
+// idFor finds the token key whose public half is pub, so a certificate kept outside the
+// token is still signed for by the key inside it.
+func (k tokenKeys) idFor(pub crypto.PublicKey) ([]byte, bool) {
+	for _, key := range k {
+		equaler, ok := key.public.(interface{ Equal(crypto.PublicKey) bool })
+		if ok && len(key.id) > 0 && equaler.Equal(pub) {
+			return key.id, true
+		}
+	}
+	return nil, false
+}
+
 func (s *PKCS11Store) String() string {
 	if s.uri.Token == "" {
 		return "PKCS#11 token"

client/internal/certproof/pkcs11store_test.go

@@ -52,15 +52,7 @@ func TestStores_KeepsFileCertificatesWhenTokenFails(t *testing.T) {
 // It imports a key and its certificate as token objects, then proves the certificate
 // through the store the way the daemon would. Every run adds one more identity to the token.
 func TestCollect_PKCS11TokenEndToEnd(t *testing.T) {
-	uri := os.Getenv(testPKCS11URIEnv)
-	if uri == "" {
-		t.Skipf("set %s to a PKCS#11 URI with a PIN to run", testPKCS11URIEnv)
-	}
-	store, err := NewPKCS11Store(PKCS11Config{URI: uri})
-	require.NoError(t, err)
-	if _, err := pkcs11.Load(store.uri.Module()); errors.Is(err, pkcs11.ErrUnsupported) {
-		t.Skip(err)
-	}
+	store, uri := pkcs11TestStore(t, "")
 
 	keys := map[string]crypto.Signer{"ecdsa": certtest.ECDSAKey(t), "rsa": certtest.RSAKey(t)}
 	for name, key := range keys {
@@ -83,25 +75,20 @@ func TestCollect_PKCS11TokenEndToEnd(t *testing.T) {
 	}
 }
 
-// Attribute and key types the import needs and the store does not.
+// Attribute types the import needs and the store does not.
 const (
 	attrPrivate         = 0x2
 	attrIssuer          = 0x81
 	attrSerialNumber    = 0x82
-	attrKeyType         = 0x100
 	attrSensitive       = 0x103
 	attrSign            = 0x108
-	attrModulus         = 0x120
-	attrPublicExponent  = 0x122
+	attrVerify          = 0x10a
 	attrPrivateExponent = 0x123
 	attrPrime1          = 0x124
 	attrPrime2          = 0x125
 	attrExponent1       = 0x126
 	attrExponent2       = 0x127
 	attrCoefficient     = 0x128
-	attrECParams        = 0x180
-	keyTypeRSA          = 0x0
-	keyTypeEC           = 0x3
 )
 
 var (
@@ -111,7 +98,71 @@ var (
 	oidP256 = []byte{0x06, 0x08, 0x2a, 0x86, 0x48, 0xce, 0x3d, 0x03, 0x01, 0x07}
 )
 
+// importIdentity stores key and leaf on the token the way tpm2_ptool import and addcert
+// do: private and public key objects plus the certificate, all under one CKA_ID.
 func importIdentity(t *testing.T, uri string, key crypto.Signer, leaf *x509.Certificate) {
+	t.Helper()
+	id := importKey(t, uri, key, leaf.Subject.CommonName)
+	importCertificate(t, uri, leaf, id)
+}
+
+func importKey(t *testing.T, uri string, key crypto.Signer, label string) []byte {
+	t.Helper()
+	session := readWriteSession(t, uri)
+	defer session.Close()
+
+	id := make([]byte, 8)
+	_, err := rand.Read(id)
+	require.NoError(t, err)
+
+	private := []pkcs11.Attribute{
+		attr(pkcs11.AttrClass, pkcs11.ULong(pkcs11.ClassPrivateKey)),
+		attr(pkcs11.AttrToken, ckTrue),
+		attr(attrPrivate, ckTrue),
+		attr(attrSensitive, ckTrue),
+		attr(attrSign, ckTrue),
+		attr(pkcs11.AttrLabel, []byte(label)),
+		attr(pkcs11.AttrID, id),
+	}
+	_, err = session.CreateObject(append(private, privateKeyAttributes(t, key)...)...)
+	require.NoError(t, err, "import private key")
+
+	public := []pkcs11.Attribute{
+		attr(pkcs11.AttrClass, pkcs11.ULong(pkcs11.ClassPublicKey)),
+		attr(pkcs11.AttrToken, ckTrue),
+		attr(attrPrivate, ckFalse),
+		attr(attrVerify, ckTrue),
+		attr(pkcs11.AttrLabel, []byte(label)),
+		attr(pkcs11.AttrID, id),
+	}
+	_, err = session.CreateObject(append(public, publicKeyAttributes(t, key)...)...)
+	require.NoError(t, err, "import public key")
+	return id
+}
+
+func importCertificate(t *testing.T, uri string, leaf *x509.Certificate, id []byte) {
+	t.Helper()
+	session := readWriteSession(t, uri)
+	defer session.Close()
+
+	serial, err := asn1.Marshal(leaf.SerialNumber)
+	require.NoError(t, err)
+	_, err = session.CreateObject(
+		attr(pkcs11.AttrClass, pkcs11.ULong(pkcs11.ClassCertificate)),
+		attr(pkcs11.AttrCertificateType, pkcs11.ULong(pkcs11.CertificateX509)),
+		attr(pkcs11.AttrToken, ckTrue),
+		attr(attrPrivate, ckFalse),
+		attr(pkcs11.AttrLabel, []byte(leaf.Subject.CommonName)),
+		attr(pkcs11.AttrID, id),
+		attr(pkcs11.AttrSubject, leaf.RawSubject),
+		attr(attrIssuer, leaf.RawIssuer),
+		attr(attrSerialNumber, serial),
+		attr(pkcs11.AttrValue, leaf.Raw),
+	)
+	require.NoError(t, err, "import certificate")
+}
+
+func readWriteSession(t *testing.T, uri string) *pkcs11.Session {
 	t.Helper()
 	parsed, err := pkcs11.ParseURI(uri)
 	require.NoError(t, err)
@@ -121,57 +172,24 @@ func importIdentity(t *testing.T, uri string, key crypto.Signer, leaf *x509.Cert
 	require.NoError(t, err)
 	session, err := module.OpenReadWriteSession(parsed.Token, pin)
 	require.NoError(t, err)
-	defer session.Close()
-
-	id := make([]byte, 8)
-	_, err = rand.Read(id)
-	require.NoError(t, err)
-	label := []byte(leaf.Subject.CommonName)
-	serial, err := asn1.Marshal(leaf.SerialNumber)
-	require.NoError(t, err)
-
-	_, err = session.CreateObject(
-		attr(pkcs11.AttrClass, pkcs11.ULong(pkcs11.ClassCertificate)),
-		attr(pkcs11.AttrCertificateType, pkcs11.ULong(pkcs11.CertificateX509)),
-		attr(pkcs11.AttrToken, ckTrue),
-		attr(attrPrivate, ckFalse),
-		attr(pkcs11.AttrLabel, label),
-		attr(pkcs11.AttrID, id),
-		attr(pkcs11.AttrSubject, leaf.RawSubject),
-		attr(attrIssuer, leaf.RawIssuer),
-		attr(attrSerialNumber, serial),
-		attr(pkcs11.AttrValue, leaf.Raw),
-	)
-	require.NoError(t, err, "import certificate")
-
-	template := []pkcs11.Attribute{
-		attr(pkcs11.AttrClass, pkcs11.ULong(pkcs11.ClassPrivateKey)),
-		attr(pkcs11.AttrToken, ckTrue),
-		attr(attrPrivate, ckTrue),
-		attr(attrSensitive, ckTrue),
-		attr(attrSign, ckTrue),
-		attr(pkcs11.AttrLabel, label),
-		attr(pkcs11.AttrID, id),
-	}
-	_, err = session.CreateObject(append(template, keyAttributes(t, key)...)...)
-	require.NoError(t, err, "import private key")
+	return session
 }
 
-func keyAttributes(t *testing.T, key crypto.Signer) []pkcs11.Attribute {
+func privateKeyAttributes(t *testing.T, key crypto.Signer) []pkcs11.Attribute {
 	t.Helper()
 	switch k := key.(type) {
 	case *ecdsa.PrivateKey:
 		return []pkcs11.Attribute{
-			attr(attrKeyType, pkcs11.ULong(keyTypeEC)),
-			attr(attrECParams, oidP256),
+			attr(pkcs11.AttrKeyType, pkcs11.ULong(pkcs11.KeyEC)),
+			attr(pkcs11.AttrECParams, oidP256),
 			attr(pkcs11.AttrValue, k.D.FillBytes(make([]byte, 32))),
 		}
 	case *rsa.PrivateKey:
 		k.Precompute()
 		return []pkcs11.Attribute{
-			attr(attrKeyType, pkcs11.ULong(keyTypeRSA)),
-			attr(attrModulus, k.N.Bytes()),
-			attr(attrPublicExponent, big.NewInt(int64(k.E)).Bytes()),
+			attr(pkcs11.AttrKeyType, pkcs11.ULong(pkcs11.KeyRSA)),
+			attr(pkcs11.AttrModulus, k.N.Bytes()),
+			attr(pkcs11.AttrPublicExponent, big.NewInt(int64(k.E)).Bytes()),
 			attr(attrPrivateExponent, k.D.Bytes()),
 			attr(attrPrime1, k.Primes[0].Bytes()),
 			attr(attrPrime2, k.Primes[1].Bytes()),
@@ -184,10 +202,107 @@ func keyAttributes(t *testing.T, key crypto.Signer) []pkcs11.Attribute {
 	return nil
 }
 
+// publicKeyAttributes describes the CKO_PUBLIC_KEY object tokens keep next to a private
+// key, which is what the store reads to pair a certificate file with its key.
+func publicKeyAttributes(t *testing.T, key crypto.Signer) []pkcs11.Attribute {
+	t.Helper()
+	switch k := key.(type) {
+	case *ecdsa.PrivateKey:
+		point := append([]byte{4}, k.X.FillBytes(make([]byte, 32))...)
+		point = append(point, k.Y.FillBytes(make([]byte, 32))...)
+		wrapped, err := asn1.Marshal(point)
+		require.NoError(t, err)
+		return []pkcs11.Attribute{
+			attr(pkcs11.AttrKeyType, pkcs11.ULong(pkcs11.KeyEC)),
+			attr(pkcs11.AttrECParams, oidP256),
+			attr(pkcs11.AttrECPoint, wrapped),
+		}
+	case *rsa.PrivateKey:
+		return []pkcs11.Attribute{
+			attr(pkcs11.AttrKeyType, pkcs11.ULong(pkcs11.KeyRSA)),
+			attr(pkcs11.AttrModulus, k.N.Bytes()),
+			attr(pkcs11.AttrPublicExponent, big.NewInt(int64(k.E)).Bytes()),
+		}
+	}
+	t.Fatalf("unsupported key %T", key)
+	return nil
+}
+
 func attr(typ uint, value []byte) pkcs11.Attribute {
 	return pkcs11.Attribute{Type: typ, Value: value}
 }
 
+// pkcs11TestStore builds the store for the token NB_TEST_PKCS11_URI names, skipping when
+// no token is configured or this build lacks PKCS#11 support.
+func pkcs11TestStore(t *testing.T, certDir string) (*PKCS11Store, string) {
+	t.Helper()
+	uri := os.Getenv(testPKCS11URIEnv)
+	if uri == "" {
+		t.Skipf("set %s to a PKCS#11 URI with a PIN to run", testPKCS11URIEnv)
+	}
+	store, err := NewPKCS11Store(PKCS11Config{URI: uri}, certDir)
+	require.NoError(t, err)
+	if _, err := pkcs11.Load(store.uri.Module()); errors.Is(err, pkcs11.ErrUnsupported) {
+		t.Skip(err)
+	}
+	return store, uri
+}
+
+// TestCollect_PKCS11KeyWithFileCertificate covers the split layout: the key lives on the
+// token, the certificate is a PEM file in the directory, and the two are paired by public
+// key because nothing on the token carries the certificate's CKA_ID.
+func TestCollect_PKCS11KeyWithFileCertificate(t *testing.T) {
+	dir := t.TempDir()
+	store, uri := pkcs11TestStore(t, dir)
+
+	keys := map[string]crypto.Signer{"ecdsa": certtest.ECDSAKey(t), "rsa": certtest.RSAKey(t)}
+	for name, key := range keys {
+		t.Run(name, func(t *testing.T) {
+			ca := certtest.NewCA(t, "corp-file-"+name)
+			leaf := ca.Issue(t, key, "device-file-"+name)
+			importKey(t, uri, key, "device-file-"+name)
+			writeFile(t, dir, "device-"+name+".pem", certtest.CertPEM(leaf))
+
+			challenger := certposture.NewChallenger([]byte("secret"))
+			now := time.Now()
+			nonce := challenger.Nonce(peerKey, now)
+			checks := []*proto.Checks{{CertificateChallenge: &proto.CertificateChallenge{Nonce: nonce, CaCertificates: []string{ca.PEM}}}}
+
+			proofs := Collect(context.Background(), store, checks, peerKey)
+			require.Len(t, proofs, 1, "the token key must prove the certificate kept on disk")
+			chain, err := challenger.Verify(proofs[0], peerKey, now)
+			require.NoError(t, err)
+			assert.True(t, leaf.Equal(chain[0]), "proof must carry the certificate from the directory")
+		})
+	}
+}
+
+func TestPKCS11Store_FileChains(t *testing.T) {
+	ca := certtest.NewCA(t, "corp")
+	dir := t.TempDir()
+	// Only certificate files without a key of their own belong to the token; the file
+	// store answers for the others, and non-certificate files are ignored.
+	writeFile(t, dir, "device.pem", certtest.CertPEM(ca.Issue(t, certtest.ECDSAKey(t), "device")))
+	writeFile(t, dir, "ca.crt", ca.PEM)
+	keyed := certtest.ECDSAKey(t)
+	writeFile(t, dir, "inline.pem", certtest.CertPEM(ca.Issue(t, keyed, "inline"))+certtest.KeyPEM(t, keyed))
+	writeFile(t, dir, "sibling.crt", certtest.CertPEM(ca.Issue(t, keyed, "sibling")))
+	writeFile(t, dir, "sibling.key", certtest.KeyPEM(t, keyed))
+	writeFile(t, dir, "notes.txt", "not a certificate")
+
+	chains, err := (&PKCS11Store{uri: &pkcs11.URI{}, certDir: dir}).fileChains()
+	require.NoError(t, err)
+	var subjects []string
+	for _, chain := range chains {
+		subjects = append(subjects, chain[0].Subject.CommonName)
+	}
+	assert.ElementsMatch(t, []string{"device", "corp"}, subjects, "only key-less certificate files are left to the token")
+
+	chains, err = (&PKCS11Store{uri: &pkcs11.URI{}}).fileChains()
+	require.NoError(t, err)
+	assert.Empty(t, chains, "no directory configured means no file certificates")
+}
+
 func TestNewPKCS11Store_PIN(t *testing.T) {
 	tests := []struct {
 		name       string
@@ -202,7 +317,7 @@ func TestNewPKCS11Store_PIN(t *testing.T) {
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			store, err := NewPKCS11Store(tt.cfg)
+			store, err := NewPKCS11Store(tt.cfg, "")
 			require.NoError(t, err)
 			pin, err := store.userPIN()
 			require.NoError(t, err)
@@ -211,6 +326,6 @@ func TestNewPKCS11Store_PIN(t *testing.T) {
 		})
 	}
 
-	_, err := NewPKCS11Store(PKCS11Config{URI: "not-a-pkcs11-uri", PIN: "1234"})
+	_, err := NewPKCS11Store(PKCS11Config{URI: "not-a-pkcs11-uri", PIN: "1234"}, "")
 	assert.Error(t, err, "a malformed URI must not be silently replaced by the defaults")
 }

client/internal/certproof/store.go

@@ -33,6 +33,21 @@ type Store interface {
 	Candidates(ctx context.Context) ([]Candidate, error)
 }
 
+// Config selects where the Linux daemon looks for certificates: Dir is the PEM directory,
+// empty for NB_CERT_STORE_DIR or /etc/netbird/certs, and PKCS11 names a token whose keys
+// sign for certificates on the token or in that directory.
+type Config struct {
+	Dir    string
+	PKCS11 PKCS11Config
+}
+
+func (c Config) dir() string {
+	if c.Dir != "" {
+		return c.Dir
+	}
+	return StoreDir()
+}
+
 // FileStore reads PEM files from a directory. A file holds the chain (leaf first) and
 // either its private key or a sibling "<name>.key" file holds it. The key is a plain
 // PKCS#8, EC or RSA key, or a TSS2 key the TPM signs with.
@@ -52,55 +67,76 @@ func StoreDir() string {
 }
 
 func (s *FileStore) Candidates(_ context.Context) ([]Candidate, error) {
-	entries, err := os.ReadDir(s.dir)
-	if errors.Is(err, os.ErrNotExist) {
-		return nil, nil
-	}
+	paths, err := certFiles(s.dir)
 	if err != nil {
-		return nil, fmt.Errorf("read certificate store %s: %w", s.dir, err)
+		return nil, err
 	}
 
 	var candidates []Candidate
-	for _, entry := range entries {
-		if entry.IsDir() || !isCertFile(entry.Name()) {
-			continue
-		}
-		path := filepath.Join(s.dir, entry.Name())
-		candidate, err := s.load(path)
+	for _, path := range paths {
+		chain, signer, err := loadPEM(path)
 		if err != nil {
 			log.Warnf("skipping certificate %s: %v", path, err)
 			continue
 		}
-		candidates = append(candidates, candidate)
+		if signer == nil {
+			log.Debugf("certificate %s has no key file, only a token can sign for it", path)
+			continue
+		}
+		candidates = append(candidates, Candidate{Chain: chain, Signer: signer})
 	}
 	return candidates, nil
 }
 
-func (s *FileStore) load(path string) (Candidate, error) {
+// certFiles lists the certificate files in dir, none when the directory does not exist.
+func certFiles(dir string) ([]string, error) {
+	entries, err := os.ReadDir(dir)
+	if errors.Is(err, os.ErrNotExist) {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, fmt.Errorf("read certificate store %s: %w", dir, err)
+	}
+	var paths []string
+	for _, entry := range entries {
+		if !entry.IsDir() && isCertFile(entry.Name()) {
+			paths = append(paths, filepath.Join(dir, entry.Name()))
+		}
+	}
+	return paths, nil
+}
+
+// loadPEM reads a certificate file and its private key, held in the file itself or in
+// the sibling "<name>.key" file. The signer is nil when neither holds a key.
+func loadPEM(path string) ([]*x509.Certificate, crypto.Signer, error) {
 	data, err := os.ReadFile(path)
 	if err != nil {
-		return Candidate{}, err
+		return nil, nil, err
 	}
 	chain, signer, err := parsePEM(data)
 	if err != nil {
-		return Candidate{}, err
+		return nil, nil, err
 	}
 	if len(chain) == 0 {
-		return Candidate{}, errors.New("no certificate")
+		return nil, nil, errors.New("no certificate")
+	}
+	if signer != nil {
+		return chain, signer, nil
+	}
+	keyData, err := os.ReadFile(strings.TrimSuffix(path, filepath.Ext(path)) + ".key")
+	if errors.Is(err, os.ErrNotExist) {
+		return chain, nil, nil
+	}
+	if err != nil {
+		return nil, nil, fmt.Errorf("read key file: %w", err)
+	}
+	if _, signer, err = parsePEM(keyData); err != nil {
+		return nil, nil, err
 	}
 	if signer == nil {
-		keyData, err := os.ReadFile(strings.TrimSuffix(path, filepath.Ext(path)) + ".key")
-		if err != nil {
-			return Candidate{}, fmt.Errorf("no private key: %w", err)
-		}
-		if _, signer, err = parsePEM(keyData); err != nil {
-			return Candidate{}, err
-		}
-		if signer == nil {
-			return Candidate{}, errors.New("no private key in key file")
-		}
+		return nil, nil, errors.New("no private key in key file")
 	}
-	return Candidate{Chain: chain, Signer: signer}, nil
+	return chain, signer, nil
 }
 
 func parsePEM(data []byte) ([]*x509.Certificate, crypto.Signer, error) {

client/internal/certproof/store_other.go

@@ -9,13 +9,14 @@ func DefaultStore() Store {
 	return NewFileStore(StoreDir())
 }
 
-// storeWithToken joins DefaultStore with the PKCS#11 token cfg names, when it names one.
-func storeWithToken(cfg PKCS11Config) Store {
-	files := DefaultStore()
-	if cfg.URI == "" && cfg.PIN == "" {
+// storeWithToken reads the PEM directory cfg names, joined by the PKCS#11 token when cfg
+// names one. The token pairs the directory's key-less certificates with its own keys.
+func storeWithToken(cfg Config) Store {
+	files := NewFileStore(cfg.dir())
+	if cfg.PKCS11.URI == "" && cfg.PKCS11.PIN == "" {
 		return files
 	}
-	token, err := NewPKCS11Store(cfg)
+	token, err := NewPKCS11Store(cfg.PKCS11, cfg.dir())
 	if err != nil {
 		log.Warnf("ignoring PKCS#11 URI: %v", err)
 		return files

client/internal/certproof/store_other_test.go

@@ -6,20 +6,31 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestStoreWithToken(t *testing.T) {
-	assert.IsType(t, &FileStore{}, storeWithToken(PKCS11Config{}), "nothing configured reads the PEM directory alone")
-	assert.IsType(t, &FileStore{}, storeWithToken(PKCS11Config{URI: "not-a-pkcs11-uri"}), "an invalid URI must not hide the PEM directory")
+	dir := t.TempDir()
+
+	files, ok := storeWithToken(Config{Dir: dir}).(*FileStore)
+	require.True(t, ok, "a directory alone reads that directory alone")
+	assert.Equal(t, dir, files.dir, "the configured directory replaces the default")
+
+	files, ok = storeWithToken(Config{}).(*FileStore)
+	require.True(t, ok, "nothing configured reads the PEM directory alone")
+	assert.Equal(t, StoreDir(), files.dir, "no directory configured falls back to the environment or the default")
+
+	assert.IsType(t, &FileStore{}, storeWithToken(Config{PKCS11: PKCS11Config{URI: "not-a-pkcs11-uri"}}), "an invalid URI must not hide the PEM directory")
 
 	for name, cfg := range map[string]PKCS11Config{
 		"pin alone": {PIN: "1234"},
 		"uri alone": {URI: "pkcs11:token=netbird?pin-value=1234"},
 	} {
-		store, ok := storeWithToken(cfg).(Stores)
-		if assert.True(t, ok, "%s joins the token to the PEM directory", name) {
-			assert.Len(t, store, 2, name)
-			assert.IsType(t, &PKCS11Store{}, store[1], name)
-		}
+		store, ok := storeWithToken(Config{Dir: dir, PKCS11: cfg}).(Stores)
+		require.True(t, ok, "%s joins the token to the PEM directory", name)
+		require.Len(t, store, 2, name)
+		token, ok := store[1].(*PKCS11Store)
+		require.True(t, ok, name)
+		assert.Equal(t, dir, token.certDir, "%s: the token pairs certificates from the same directory", name)
 	}
 }