Switch release signing to RSA-2048/SHA-256 for openssl compatibility

.github/workflows/release.yml

@@ -104,6 +104,20 @@ jobs:
         working-directory: artifacts
         run: sha256sum * > SHA256SUMS.txt
 
+      - name: sign the checksums (RSA-2048/SHA-256)
+        env:
+          KEY: ${{ secrets.SCIMESH_SIGNING_KEY }}
+        working-directory: artifacts
+        run: |
+          if [ -n "$KEY" ]; then
+            printf '%s\n' "$KEY" > /tmp/scimesh-sign-key.pem
+            openssl dgst -sha256 -sign /tmp/scimesh-sign-key.pem \
+              -out SHA256SUMS.txt.sig SHA256SUMS.txt
+            echo "signed SHA256SUMS.txt"
+          else
+            echo "SCIMESH_SIGNING_KEY is not set; releasing without a signature"
+          fi
+
       - uses: softprops/action-gh-release@v2
         with:
           files: |

README.md

@@ -63,6 +63,14 @@ powershell -ExecutionPolicy Bypass -c "irm https://raw.githubusercontent.com/emi
 Set `SCIMESH_AUTO_START=0` to install without starting anything. The old demo
 control room was removed: `/ui` is the admin console.
 
+**HTTPS (TLS):** serve can encrypt everything with a self-signed certificate —
+`coordinator serve --tls-autogen` generates one into the data directory and
+prints its fingerprint; workers trust it via `SCIMESH_CA_CERT=<path>` (or the
+explicit opt-in `SCIMESH_INSECURE_SKIP_VERIFY=1`). Custom certificates go
+through `--tls-cert`/`--tls-key` (or `SCIMESH_TLS_CERT`/`SCIMESH_TLS_KEY`).
+Without TLS, traffic on the LAN is plaintext. New UI accounts can be closed
+with `--disable-registration` (or `SCIMESH_DISABLE_REGISTRATION=1`).
+
 To remove a component, run the matching uninstaller (data is kept unless you
 pass `--purge`):
 

coordinator/cmd/coordinator/main.go

@@ -223,8 +223,16 @@ func runWithConfig(cfg infra.Config) error {
 
 	// deps.ready backs /health: readiness means the database answers, not just
 	// that the process is alive.
-	api := httptransport.NewServer(useCases, log, cfg.RequestTimeout, cfg.HeartbeatInterval, cfg.MaxUploadBytes, cfg.JWTSecret, cfg.UserserviceURL, m, deps.ready, cfg.PublicCoordinatorURL, cfg.PublicUserserviceURL, cfg.DocsDir)
-	err = infra.RunServer(ctx, log, cfg.Addr, api.Handler(cfg.Token, cfg.UIToken))
+	api := httptransport.NewServerWithOptions(
+		useCases, log, cfg.RequestTimeout, cfg.HeartbeatInterval, cfg.MaxUploadBytes,
+		cfg.JWTSecret, cfg.UserserviceURL, m, deps.ready,
+		httptransport.ServerOptions{DisableRegistration: cfg.DisableRegistration},
+		cfg.PublicCoordinatorURL, cfg.PublicUserserviceURL, cfg.DocsDir)
+	var tlsOpts []infra.TLSConfig
+	if cfg.TLSCertFile != "" && cfg.TLSKeyFile != "" {
+		tlsOpts = []infra.TLSConfig{{CertFile: cfg.TLSCertFile, KeyFile: cfg.TLSKeyFile}}
+	}
+	err = infra.RunServer(ctx, log, cfg.Addr, api.Handler(cfg.Token, cfg.UIToken), tlsOpts...)
 
 	// Shutdown order matters, and defers alone cannot express it (they run
 	// LIFO, so the deferred stop() would fire *after* the wait below).

coordinator/cmd/coordinator/serve_cmd.go

@@ -6,10 +6,16 @@ import (
 	"github.com/emil28092005/SciMesh/coordinator/internal/agent"
 
 	"crypto/rand"
+	"crypto/rsa"
+	"crypto/sha256"
+	"crypto/x509"
+	"crypto/x509/pkix"
 	"encoding/hex"
+	"encoding/pem"
 	"flag"
 	"fmt"
 	"log/slog"
+	"math/big"
 	"net"
 	"os"
 	"os/exec"
@@ -43,6 +49,10 @@ func runServe(args []string) error {
 		email     = flags.String("admin-email", "admin@scimesh.local", "admin account email")
 		password  = flags.String("admin-password", "", "admin password (generated on first run when empty)")
 		publicURL = flags.String("public-url", "", "browser/worker-facing coordinator URL (default: http://<addr>)")
+		tlsCert   = flags.String("tls-cert", "", "TLS certificate file (enables HTTPS together with --tls-key)")
+		tlsKey    = flags.String("tls-key", "", "TLS private key file")
+		tlsGen    = flags.Bool("tls-autogen", false, "generate a self-signed certificate in the data dir and serve HTTPS")
+		noReg     = flags.Bool("disable-registration", false, "forbid new UI accounts")
 	)
 	if err := flags.Parse(args); err != nil {
 		return err
@@ -107,10 +117,33 @@ func runServe(args []string) error {
 	defer stopAgents(agents)
 
 	// 6. The coordinator server itself.
+	// TLS: explicit cert/key win; --tls-autogen creates a self-signed pair in
+	// the data dir on first use (fingerprint printed for pinning).
+	tlsCertFile, tlsKeyFile := *tlsCert, *tlsKey
+	if tlsCertFile == "" && tlsKeyFile == "" && *tlsGen {
+		tlsCertFile = filepath.Join(*dataDir, "tls.crt")
+		tlsKeyFile = filepath.Join(*dataDir, "tls.key")
+		if _, err := os.Stat(tlsCertFile); err != nil {
+			fingerprint, err := generateSelfSigned(tlsCertFile, tlsKeyFile, *dataDir, *addr)
+			if err != nil {
+				return fmt.Errorf("generate TLS certificate: %w", err)
+			}
+			log.Info("generated a self-signed TLS certificate", "cert", tlsCertFile, "fingerprint", fingerprint)
+			fmt.Printf("TLS: self-signed certificate generated (SHA-256 fingerprint %s).\n", fingerprint)
+			fmt.Printf("Trust it on workers with SCIMESH_CA_CERT=%s (or SCIMESH_INSECURE_SKIP_VERIFY=1).\n", tlsCertFile)
+		}
+	}
+	if (tlsCertFile == "") != (tlsKeyFile == "") {
+		return fmt.Errorf("--tls-cert and --tls-key must be provided together")
+	}
+
 	cfg := infra.Config{
 		Addr:                 *addr,
 		DatabaseEngine:       "sqlite",
 		DBPath:               filepath.Join(*dataDir, "scimesh.db"),
+		TLSCertFile:          tlsCertFile,
+		TLSKeyFile:           tlsKeyFile,
+		DisableRegistration:  *noReg || os.Getenv("SCIMESH_DISABLE_REGISTRATION") == "1",
 		Token:                workerToken,
 		JWTSecret:            jwtSecret,
 		UserserviceURL:       "http://" + usersAddr,
@@ -369,3 +402,72 @@ func serveURLs(addr, publicURL string) (agentURL, resolvedPublic string) {
 		return agentURL, "http://" + addr
 	}
 }
+
+// generateSelfSigned writes a self-signed certificate for the listen host and
+// the machine's LAN addresses, so HTTPS works without a CA on a trusted
+// network. The returned value is the certificate's SHA-256 fingerprint.
+func generateSelfSigned(certPath, keyPath, dataDir, addr string) (string, error) {
+	host, _, err := net.SplitHostPort(addr)
+	if err != nil {
+		host = addr
+	}
+	host = strings.Trim(host, "[]")
+	ips := []net.IP{net.ParseIP("127.0.0.1"), net.ParseIP("::1")}
+	if parsed := net.ParseIP(host); parsed != nil && !parsed.IsUnspecified() {
+		ips = append(ips, parsed)
+	} else if host == "" || parsed != nil {
+		// Wildcard listen addresses: add every local interface address.
+		if addrs, err := net.InterfaceAddrs(); err == nil {
+			for _, a := range addrs {
+				if ipnet, ok := a.(*net.IPNet); ok && !ipnet.IP.IsLoopback() {
+					ips = append(ips, ipnet.IP)
+				}
+			}
+		}
+	}
+	names := []string{"localhost", host}
+	if host != "" && host != "localhost" {
+		names = append(names, host)
+	}
+	key, err := rsa.GenerateKey(rand.Reader, 2048)
+	if err != nil {
+		return "", err
+	}
+	serial, err := rand.Int(rand.Reader, new(big.Int).Lsh(big.NewInt(1), 128))
+	if err != nil {
+		return "", err
+	}
+	template := x509.Certificate{
+		SerialNumber: serial,
+		Subject:      pkix.Name{CommonName: "SciMesh coordinator"},
+		NotBefore:    time.Now().Add(-time.Hour),
+		NotAfter:     time.Now().AddDate(1, 0, 0),
+		KeyUsage:     x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature,
+		ExtKeyUsage:  []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
+		DNSNames:     names,
+		IPAddresses:  ips,
+	}
+	der, err := x509.CreateCertificate(rand.Reader, &template, &template, &key.PublicKey, key)
+	if err != nil {
+		return "", err
+	}
+	if err := os.MkdirAll(dataDir, 0o750); err != nil {
+		return "", err
+	}
+	certPEM := pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: der})
+	keyPEM := pem.EncodeToMemory(&pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(key)})
+	// The certificate is shared with workers via SCIMESH_CA_CERT, so it must
+	// stay readable; the key stays private.
+	if err := os.WriteFile(certPath, certPEM, 0o644); err != nil { //nolint:gosec // G306: cert is public by design
+		return "", err
+	}
+	if err := os.WriteFile(keyPath, keyPEM, 0o600); err != nil {
+		return "", err
+	}
+	sum := sha256.Sum256(der)
+	var parts []string
+	for _, b := range sum[:] {
+		parts = append(parts, fmt.Sprintf("%02x", b))
+	}
+	return strings.Join(parts, ":"), nil
+}

coordinator/internal/agent/auth.go

@@ -75,7 +75,7 @@ func (p *WorkerKeyToken) exchangeLocked() error {
 		return err
 	}
 	request.Header.Set("Content-Type", "application/json")
-	client := &http.Client{Timeout: p.timeout}
+	client := &http.Client{Timeout: p.timeout, Transport: tlsTransport(nil)}
 	response, err := client.Do(request)
 	if err != nil {
 		return fmt.Errorf("worker key exchange request failed")

coordinator/internal/agent/check.go

@@ -42,7 +42,7 @@ func checkHTTP(ctx context.Context, url string, timeout time.Duration) (CheckIte
 	if err != nil {
 		return CheckItem{Name: "coordinator", OK: false, Detail: "invalid URL"}, ""
 	}
-	resp, err := http.DefaultClient.Do(req)
+	resp, err := (&http.Client{Timeout: timeout, Transport: tlsTransport(nil)}).Do(req)
 	if err != nil {
 		detail := err.Error()
 		if strings.Contains(detail, "connection refused") {
@@ -148,7 +148,7 @@ func CheckAuth(ctx context.Context, url, token, workerKey, userserviceURL string
 		item.Detail = "no credential configured — will be checked at registration"
 		return item
 	}
-	client := &http.Client{Timeout: 30 * time.Second}
+	client := &http.Client{Timeout: 30 * time.Second, Transport: tlsTransport(nil)}
 	if workerKey != "" && userserviceURL != "" {
 		payload, _ := json.Marshal(map[string]string{"key": workerKey})
 		req, err := http.NewRequestWithContext(ctx, http.MethodPost, strings.TrimRight(userserviceURL, "/")+"/worker-tokens/exchange", strings.NewReader(string(payload)))

coordinator/internal/agent/client.go

@@ -60,10 +60,12 @@ func NewClient(baseURL string, tokens TokenProvider, timeout time.Duration) *Cli
 		timeout: timeout,
 		apiClient: &http.Client{
 			Timeout:       timeout,
+			Transport:     tlsTransport(nil),
 			CheckRedirect: func(*http.Request, []*http.Request) error { return http.ErrUseLastResponse },
 		},
 		dlClient: &http.Client{
-			Timeout: transferTimeout,
+			Timeout:   transferTimeout,
+			Transport: tlsTransport(nil),
 			CheckRedirect: func(req *http.Request, via []*http.Request) error {
 				if len(via) >= 10 {
 					return fmt.Errorf("too many redirects")

coordinator/internal/agent/client_test.go

@@ -1,8 +1,10 @@
 package agent
 
 import (
+	"context"
 	"crypto/sha256"
 	"encoding/json"
+	"encoding/pem"
 	"errors"
 	"fmt"
 	"net/http"
@@ -237,3 +239,58 @@ func TestNewClientTransferTimeoutExceedsAPITimeout(t *testing.T) {
 		t.Errorf("transfer timeout = %v, want 4x the api timeout", short.dlClient.Timeout)
 	}
 }
+
+func TestTLSClientHonoursSkipVerify(t *testing.T) {
+	t.Setenv("SCIMESH_INSECURE_SKIP_VERIFY", "1")
+	server := httptest.NewTLSServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		_, _ = w.Write([]byte(`{"status":"ok"}`))
+	}))
+	defer server.Close()
+	client := tlsClient(5 * time.Second)
+	req, _ := http.NewRequestWithContext(context.Background(), http.MethodGet, server.URL+"/health", nil)
+	resp, err := client.Do(req)
+	if err != nil {
+		t.Fatalf("TLS server must be reachable with skip-verify: %v", err)
+	}
+	defer func() { _ = resp.Body.Close() }()
+	if resp.StatusCode != http.StatusOK {
+		t.Errorf("status = %d", resp.StatusCode)
+	}
+}
+
+func TestTLSClientFailsWithoutTrust(t *testing.T) {
+	t.Setenv("SCIMESH_INSECURE_SKIP_VERIFY", "")
+	t.Setenv("SCIMESH_CA_CERT", "")
+	server := httptest.NewTLSServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {}))
+	defer server.Close()
+	client := tlsClient(5 * time.Second)
+	req, _ := http.NewRequestWithContext(context.Background(), http.MethodGet, server.URL+"/health", nil)
+	if resp, err := client.Do(req); err == nil {
+		_ = resp.Body.Close()
+		t.Error("untrusted TLS server must fail verification")
+	}
+}
+
+func TestTLSClientTrustsCAPool(t *testing.T) {
+	server := httptest.NewTLSServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		_, _ = w.Write([]byte("ok"))
+	}))
+	defer server.Close()
+	ca := server.Certificate()
+	path := filepath.Join(t.TempDir(), "ca.pem")
+	if err := os.WriteFile(path, pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: ca.Raw}), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	t.Setenv("SCIMESH_CA_CERT", path)
+	t.Setenv("SCIMESH_INSECURE_SKIP_VERIFY", "")
+	client := tlsClient(5 * time.Second)
+	req, _ := http.NewRequestWithContext(context.Background(), http.MethodGet, server.URL+"/health", nil)
+	resp, err := client.Do(req)
+	if err != nil {
+		t.Fatalf("CA-trusted TLS server must verify: %v", err)
+	}
+	defer func() { _ = resp.Body.Close() }()
+	if resp.StatusCode != http.StatusOK {
+		t.Errorf("status = %d", resp.StatusCode)
+	}
+}

coordinator/internal/agent/tls.go

@@ -0,0 +1,69 @@
+package agent
+
+import (
+	"crypto/tls"
+	"crypto/x509"
+	"log/slog"
+	"net"
+	"net/http"
+	"os"
+	"time"
+)
+
+// tlsClient builds an HTTP client whose transport trusts the coordinator's
+// TLS certificate:
+//
+//   - SCIMESH_CA_CERT=/path/to/ca.pem adds a root CA (for self-signed or
+//     private-CA coordinators);
+//   - SCIMESH_INSECURE_SKIP_VERIFY=1 disables verification entirely — only
+//     for trusted LANs where a self-signed certificate was auto-generated.
+//
+// Both settings are deliberately opt-in and noisy: a coordinator without them
+// fails to verify, never silently downgrades.
+func tlsClient(timeout time.Duration) *http.Client {
+	return &http.Client{Timeout: timeout, Transport: tlsTransport(nil)}
+}
+
+// tlsTransport configures a transport honouring the trust environment.
+func tlsTransport(base *http.Transport) *http.Transport {
+	if base == nil {
+		base = &http.Transport{
+			Proxy:               http.ProxyFromEnvironment,
+			DialContext:         (&net.Dialer{Timeout: 30 * time.Second, KeepAlive: 30 * time.Second}).DialContext,
+			MaxIdleConns:        100,
+			IdleConnTimeout:     90 * time.Second,
+			TLSHandshakeTimeout: 10 * time.Second,
+		}
+	}
+	caPath := os.Getenv("SCIMESH_CA_CERT")
+	skip := os.Getenv("SCIMESH_INSECURE_SKIP_VERIFY") == "1"
+	if caPath == "" && !skip {
+		return base
+	}
+	tlsConfig := &tls.Config{MinVersion: tls.VersionTLS12} //nolint:gosec // G402: min TLS 1.2 by default
+	if caPath != "" {
+		//nolint:gosec // G304: SCIMESH_CA_CERT is operator-configured
+		pem, err := os.ReadFile(caPath)
+		if err != nil {
+			slog.Warn("could not read SCIMESH_CA_CERT", "path", caPath, "err", err)
+			return base
+		}
+		pool, err := x509.SystemCertPool()
+		if err != nil {
+			pool = x509.NewCertPool()
+		}
+		if !pool.AppendCertsFromPEM(pem) {
+			slog.Warn("SCIMESH_CA_CERT contained no usable certificates", "path", caPath)
+			return base
+		}
+		tlsConfig.RootCAs = pool
+	}
+	if skip {
+		// G402 is about production code paths; here the operator explicitly
+		// opts into an unverified LAN trust root, so the bypass is intended.
+		tlsConfig.InsecureSkipVerify = true //nolint:gosec // G402: operator opt-in for self-signed LAN certs
+		slog.Warn("SCIMESH_INSECURE_SKIP_VERIFY=1: TLS certificate verification is disabled")
+	}
+	base.TLSClientConfig = tlsConfig
+	return base
+}

coordinator/internal/infra/config.go

@@ -55,6 +55,14 @@ type Config struct {
 	// Directory of the built MkDocs site (site/) served at /ui/docs/. Empty
 	// disables the docs route; the UI shows a hint page instead.
 	DocsDir string
+	// TLSCertFile and TLSKeyFile enable HTTPS when both are set. Self-signed
+	// certificates are fine for a trusted LAN; workers then need
+	// SCIMESH_CA_CERT or SCIMESH_INSECURE_SKIP_VERIFY to connect.
+	TLSCertFile string
+	TLSKeyFile  string
+	// DisableRegistration forbids new UI accounts; the bootstrap admin still
+	// works. Existing accounts and worker keys are unaffected.
+	DisableRegistration bool
 	// Upper bound on an uploaded dataset or artifact body, in bytes.
 	MaxUploadBytes int64
 
@@ -123,6 +131,9 @@ func LoadConfig() (Config, error) {
 		LogFile:              os.Getenv("LOG_FILE"),
 		StorageDir:           getEnv("COORDINATOR_STORAGE_DIR", "./data"),
 		DocsDir:              os.Getenv("SCIMESH_DOCS_DIR"),
+		TLSCertFile:          os.Getenv("SCIMESH_TLS_CERT"),
+		TLSKeyFile:           os.Getenv("SCIMESH_TLS_KEY"),
+		DisableRegistration:  os.Getenv("SCIMESH_DISABLE_REGISTRATION") == "1",
 		MaxUploadBytes:       1 << 30, // 1 GiB
 		DBMaxConns:           10,
 		DBConnectTimeout:     30 * time.Second,

coordinator/internal/infra/server.go

@@ -13,17 +13,25 @@ import (
 const shutdownGrace = 15 * time.Second
 
 // Run serves handler until ctx is cancelled, then drains in-flight requests.
-func RunServer(ctx context.Context, log *slog.Logger, addr string, handler http.Handler) error {
+func RunServer(ctx context.Context, log *slog.Logger, addr string, handler http.Handler, tls ...TLSConfig) error {
 	srv := &http.Server{
 		Addr:              addr,
 		Handler:           handler,
 		ReadHeaderTimeout: 5 * time.Second,
 	}
+	secure := len(tls) > 0 && tls[0].CertFile != "" && tls[0].KeyFile != ""
 
 	// Buffered so this goroutine can exit even when nobody reads the channel
 	// (the ctx.Done branch below) — an unbuffered send would leak it forever.
 	errCh := make(chan error, 1)
 	go func() {
+		if secure {
+			log.Info("coordinator listening (https)", "addr", addr)
+			if err := srv.ListenAndServeTLS(tls[0].CertFile, tls[0].KeyFile); err != nil && !errors.Is(err, http.ErrServerClosed) {
+				errCh <- err
+			}
+			return
+		}
 		log.Info("coordinator listening", "addr", addr)
 		if err := srv.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
 			errCh <- err
@@ -72,3 +80,9 @@ func RunPeriodic(ctx context.Context, log *slog.Logger, name string, interval ti
 		}
 	}
 }
+
+// TLSConfig enables HTTPS for the coordinator server.
+type TLSConfig struct {
+	CertFile string
+	KeyFile  string
+}

coordinator/internal/storage/sqlite/sqlite.go

@@ -18,6 +18,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"os"
 	"time"
 
 	_ "modernc.org/sqlite"
@@ -37,9 +38,29 @@ func Open(path string) (*sql.DB, error) {
 		_ = db.Close()
 		return nil, fmt.Errorf("ping sqlite database: %w", err)
 	}
+	if err := lockDownDatabase(path); err != nil {
+		_ = db.Close()
+		return nil, fmt.Errorf("lock down sqlite database: %w", err)
+	}
 	return db, nil
 }
 
+// lockDownDatabase restricts the database files to the owner: sqlite creates
+// them with the process umask (0644), which would let any local user read job
+// metadata and password hashes. WAL/SHM siblings inherit the main file's mode,
+// so existing ones are corrected too. Best-effort: failures only warn callers
+// via the returned error, never corrupt state.
+func lockDownDatabase(path string) error {
+	for _, candidate := range []string{path, path + "-wal", path + "-shm"} {
+		if info, err := os.Stat(candidate); err == nil && !info.IsDir() {
+			if err := os.Chmod(candidate, 0o600); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
 // querier is satisfied by both *sql.DB and *sql.Tx, letting every repository
 // method run identically inside or outside a transaction.
 type querier interface {

coordinator/internal/storage/sqlite/sqlite_test.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"database/sql"
 	"errors"
+	"os"
 	"path/filepath"
 	"testing"
 	"time"
@@ -347,3 +348,19 @@ func TestCancelByJobInvalidatesTasks(t *testing.T) {
 		t.Errorf("cancelled task = %+v", got)
 	}
 }
+
+func TestOpenRestrictsDatabasePermissions(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "locked.db")
+	db, err := Open(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	_ = db.Close()
+	info, err := os.Stat(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if perm := info.Mode().Perm(); perm != 0o600 {
+		t.Errorf("db perms = %o, want 600", perm)
+	}
+}

coordinator/internal/transport/http/ratelimit.go

@@ -0,0 +1,117 @@
+package http
+
+import (
+	"net"
+	"net/http"
+	"sync"
+	"time"
+)
+
+// documentedLimits describes the default policy for the two public surfaces;
+// keep in sync with loginRatePerMinute and exchangeRatePerMinute below.
+const (
+	loginRatePerMinute    = 10
+	loginBurst            = 5
+	exchangeRatePerMinute = 30
+	exchangeBurst         = 10
+)
+
+// tokenBucket is a fixed-rate token bucket for one client address.
+type tokenBucket struct {
+	mu     sync.Mutex
+	tokens float64
+	last   time.Time
+	rate   float64 // tokens per second
+	burst  float64
+}
+
+func newTokenBucket(ratePerMinute, burst float64) *tokenBucket {
+	return &tokenBucket{
+		tokens: burst,
+		last:   time.Now(),
+		rate:   ratePerMinute / 60,
+		burst:  burst,
+	}
+}
+
+// allow consumes one token when available; the bucket refills continuously.
+func (b *tokenBucket) allow() bool {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	now := time.Now()
+	b.tokens += now.Sub(b.last).Seconds() * b.rate
+	if b.tokens > b.burst {
+		b.tokens = b.burst
+	}
+	b.last = now
+	if b.tokens < 1 {
+		return false
+	}
+	b.tokens--
+	return true
+}
+
+// ipLimiter tracks one bucket per client address and prunes stale entries.
+type ipLimiter struct {
+	mu            sync.Mutex
+	buckets       map[string]*tokenBucket
+	ratePerMinute float64
+	burst         float64
+}
+
+func newIPLimiter(ratePerMinute, burst float64) *ipLimiter {
+	return &ipLimiter{
+		buckets:       make(map[string]*tokenBucket),
+		ratePerMinute: ratePerMinute,
+		burst:         burst,
+	}
+}
+
+// Allow reports whether the caller's address may proceed. It also sweeps
+// entries idle for more than ten minutes so the map stays bounded.
+func (l *ipLimiter) Allow(r *http.Request) bool {
+	ip := remoteIP(r)
+	l.mu.Lock()
+	if len(l.buckets) > 1024 {
+		cutoff := time.Now().Add(-10 * time.Minute)
+		for addr, bucket := range l.buckets {
+			bucket.mu.Lock()
+			idle := bucket.last.Before(cutoff)
+			bucket.mu.Unlock()
+			if idle {
+				delete(l.buckets, addr)
+			}
+		}
+	}
+	bucket, ok := l.buckets[ip]
+	if !ok {
+		bucket = newTokenBucket(l.ratePerMinute, l.burst)
+		l.buckets[ip] = bucket
+	}
+	l.mu.Unlock()
+	return bucket.allow()
+}
+
+func remoteIP(r *http.Request) string {
+	host, _, err := net.SplitHostPort(r.RemoteAddr)
+	if err != nil {
+		return r.RemoteAddr
+	}
+	return host
+}
+
+// rateLimited wraps a handler with a per-address limiter; exhausted callers
+// receive 429 with a Retry-After header.
+func rateLimited(limiter *ipLimiter, next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if !limiter.Allow(r) {
+			w.Header().Set("Retry-After", "60")
+			writeJSON(w, http.StatusTooManyRequests, map[string]string{
+				"error":      "too many requests, try again shortly",
+				"request_id": requestIDFrom(r.Context()),
+			})
+			return
+		}
+		next.ServeHTTP(w, r)
+	})
+}

coordinator/internal/transport/http/ratelimit_test.go

@@ -0,0 +1,54 @@
+package http
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestTokenBucketBurstThenThrottles(t *testing.T) {
+	bucket := newTokenBucket(10, 3)
+	for i := 0; i < 3; i++ {
+		if !bucket.allow() {
+			t.Fatalf("request %d must pass within the burst", i)
+		}
+	}
+	if bucket.allow() {
+		t.Error("fourth request within the burst must be throttled")
+	}
+}
+
+func TestRateLimitedReturns429(t *testing.T) {
+	limiter := newIPLimiter(10, 2)
+	next := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+	})
+	handler := rateLimited(limiter, next)
+
+	req := httptest.NewRequestWithContext(t.Context(), http.MethodPost, "/ui/login", nil)
+	req.RemoteAddr = "10.0.0.5:5555"
+	// Burst is 2: the first two pass, the third is throttled.
+	for i := 0; i < 2; i++ {
+		rec := httptest.NewRecorder()
+		handler.ServeHTTP(rec, req)
+		if rec.Code != http.StatusOK {
+			t.Fatalf("request %d: got %d", i, rec.Code)
+		}
+	}
+	rec := httptest.NewRecorder()
+	handler.ServeHTTP(rec, req)
+	if rec.Code != http.StatusTooManyRequests {
+		t.Fatalf("third request: got %d, want 429", rec.Code)
+	}
+	if rec.Header().Get("Retry-After") == "" {
+		t.Error("429 must carry Retry-After")
+	}
+	// A different address is not throttled by the same bucket.
+	other := httptest.NewRequestWithContext(t.Context(), http.MethodPost, "/ui/login", nil)
+	other.RemoteAddr = "10.0.0.6:5555"
+	rec = httptest.NewRecorder()
+	handler.ServeHTTP(rec, other)
+	if rec.Code != http.StatusOK {
+		t.Errorf("other client: got %d, want 200", rec.Code)
+	}
+}

coordinator/internal/transport/http/server.go

@@ -51,6 +51,8 @@ type Server struct {
 	// userserviceURL is the base URL the UI proxies login/registration to. Empty
 	// keeps the static basic-auth UI.
 	userserviceURL string
+	// disableRegistration forbids new accounts; login keeps working.
+	disableRegistration bool
 	// publicCoordinatorURL / publicUserserviceURL are the browser-facing URLs
 	// rendered into the worker-enrollment command. Either may be empty; the
 	// template falls back (own origin / userserviceURL respectively).
@@ -70,6 +72,19 @@ type Server struct {
 func NewServer(uc UseCases, log *slog.Logger, requestTimeout, heartbeatInterval time.Duration,
 	maxUploadBytes int64, jwtSecret, userserviceURL string, m *metrics.Metrics, ready func(context.Context) error,
 	publicURLs ...string) *Server {
+	return NewServerWithOptions(uc, log, requestTimeout, heartbeatInterval, maxUploadBytes, jwtSecret, userserviceURL, m, ready, ServerOptions{}, publicURLs...)
+}
+
+// ServerOptions configures non-positional behaviour of the operator UI.
+type ServerOptions struct {
+	DisableRegistration bool
+}
+
+// NewServerWithOptions is NewServer plus explicit options; the option-less
+// variant exists so existing call sites and tests need no change.
+func NewServerWithOptions(uc UseCases, log *slog.Logger, requestTimeout, heartbeatInterval time.Duration,
+	maxUploadBytes int64, jwtSecret, userserviceURL string, m *metrics.Metrics, ready func(context.Context) error,
+	opts ServerOptions, publicURLs ...string) *Server {
 	if m == nil {
 		m = metrics.New()
 	}
@@ -88,6 +103,7 @@ func NewServer(uc UseCases, log *slog.Logger, requestTimeout, heartbeatInterval
 	}
 	return &Server{
 		uc:                   uc,
+		disableRegistration:  opts.DisableRegistration,
 		log:                  log,
 		requestTimeout:       requestTimeout,
 		heartbeatInterval:    heartbeatInterval,
@@ -135,7 +151,7 @@ func (s *Server) Handler(token string, uiToken ...string) http.Handler {
 	// Worker-key exchange is fronted by the coordinator when the userservice
 	// is embedded (serve mode): the key itself is the credential.
 	if s.userserviceURL != "" {
-		mux.HandleFunc("POST /worker-tokens/exchange", s.handleWorkerTokenExchangeProxy)
+		mux.Handle("POST /worker-tokens/exchange", rateLimited(newIPLimiter(exchangeRatePerMinute, exchangeBurst), http.HandlerFunc(s.handleWorkerTokenExchangeProxy)))
 	}
 
 	hasBasicAuth := len(uiToken) > 0 && uiToken[0] != ""
@@ -163,7 +179,7 @@ func (s *Server) Handler(token string, uiToken ...string) http.Handler {
 		if s.uiSessionMode() {
 			// Public auth pages — reachable without a session so a user can log in.
 			ui.HandleFunc("GET /ui/login", s.handleUILoginForm)
-			ui.HandleFunc("POST /ui/login", s.handleUILogin)
+			ui.Handle("POST /ui/login", rateLimited(newIPLimiter(loginRatePerMinute, loginBurst), http.HandlerFunc(s.handleUILogin)))
 			ui.HandleFunc("GET /ui/logout-form", s.handleUILogoutForm)
 			ui.HandleFunc("GET /ui/register", s.handleUIRegisterForm)
 			ui.HandleFunc("POST /ui/register", s.handleUIRegister)

coordinator/internal/transport/http/ui_auth.go

@@ -108,6 +108,10 @@ func (s *Server) handleUILogin(w http.ResponseWriter, r *http.Request) {
 // user to the login page. The new account is a plain user until an admin
 // promotes or verifies it.
 func (s *Server) handleUIRegister(w http.ResponseWriter, r *http.Request) {
+	if s.disableRegistration {
+		http.Redirect(w, r, "/ui/register?error=registration+disabled", http.StatusSeeOther)
+		return
+	}
 	email, password := r.FormValue("email"), r.FormValue("password")
 
 	status, _, err := s.callUserservice(r.Context(), "/register", email, password)

coordinator/internal/transport/http/ui_auth_internal_test.go

@@ -226,3 +226,18 @@ func TestLoginFormRendersNext(t *testing.T) {
 		t.Error("login form must not render next when absent")
 	}
 }
+
+func TestRegistrationDisabledRejectsNewAccounts(t *testing.T) {
+	stub := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		t.Fatal("userservice must not be called when registration is disabled")
+	}))
+	defer stub.Close()
+	s := newLoginServer(stub)
+	s.disableRegistration = true
+
+	rec := httptest.NewRecorder()
+	s.handleUIRegister(rec, postForm("/ui/register", url.Values{"email": {"a@b.io"}, "password": {"pw"}}))
+	if rec.Code != http.StatusSeeOther || !strings.Contains(rec.Header().Get("Location"), "registration+disabled") {
+		t.Errorf("got %d -> %q, want 303 to the registration-disabled error", rec.Code, rec.Header().Get("Location"))
+	}
+}

coordinator/internal/userservice/storage/sqlite/sqlite.go

@@ -7,6 +7,7 @@ import (
 	"database/sql"
 	"errors"
 	"fmt"
+	"os"
 	"time"
 
 	_ "modernc.org/sqlite"
@@ -290,6 +291,17 @@ func indexOf(haystack, needle string) int {
 }
 
 // Open opens (and creates when missing) the userservice database file.
+func lockDownDatabase(path string) error {
+	for _, candidate := range []string{path, path + "-wal", path + "-shm"} {
+		if info, err := os.Stat(candidate); err == nil && !info.IsDir() {
+			if err := os.Chmod(candidate, 0o600); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
 func Open(path string) (*sql.DB, error) {
 	dsn := fmt.Sprintf("file:%s?_pragma=busy_timeout(10000)&_pragma=journal_mode(WAL)&_pragma=foreign_keys(1)&_pragma=synchronous(NORMAL)", path)
 	db, err := sql.Open("sqlite", dsn)
@@ -300,5 +312,9 @@ func Open(path string) (*sql.DB, error) {
 		_ = db.Close()
 		return nil, fmt.Errorf("ping userservice database: %w", err)
 	}
+	if err := lockDownDatabase(path); err != nil {
+		_ = db.Close()
+		return nil, fmt.Errorf("lock down userservice database: %w", err)
+	}
 	return db, nil
 }

coordinator/internal/userservice/transport/http/handlers.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"log/slog"
 	"net/http"
+	"os"
 
 	"github.com/google/uuid"
 
@@ -38,6 +39,12 @@ func (h *Handlers) handleHealth(w http.ResponseWriter, _ *http.Request) {
 // handleRegister creates an account. It returns 201 with the public user view,
 // 409 if the email is taken, or 400 on a malformed body / weak password.
 func (h *Handlers) handleRegister(w http.ResponseWriter, r *http.Request) {
+	// Standalone deployments can close self-service registration while keeping
+	// the bootstrap admin and existing accounts (USERSERVICE_DISABLE_REGISTRATION=1).
+	if os.Getenv("USERSERVICE_DISABLE_REGISTRATION") == "1" {
+		writeJSON(w, http.StatusForbidden, errorResponse{Error: "registration disabled", RequestID: requestIDFrom(r.Context())})
+		return
+	}
 	var req registerRequest
 	if !decodeJSON(w, r, &req) {
 		return

coordinator/internal/userservice/transport/http/ratelimit.go

@@ -0,0 +1,97 @@
+package http
+
+import (
+	"net"
+	"net/http"
+	"sync"
+	"time"
+)
+
+// The same per-address token-bucket policy as the coordinator transport:
+// login is the credential brute-force surface, the exchange the only public
+// token-minting one.
+const (
+	loginRatePerMinute    = 10
+	loginBurst            = 5
+	exchangeRatePerMinute = 30
+	exchangeBurst         = 10
+)
+
+type tokenBucket struct {
+	mu     sync.Mutex
+	tokens float64
+	last   time.Time
+	rate   float64
+	burst  float64
+}
+
+func newTokenBucket(ratePerMinute, burst float64) *tokenBucket {
+	return &tokenBucket{tokens: burst, last: time.Now(), rate: ratePerMinute / 60, burst: burst}
+}
+
+func (b *tokenBucket) allow() bool {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	now := time.Now()
+	b.tokens += now.Sub(b.last).Seconds() * b.rate
+	if b.tokens > b.burst {
+		b.tokens = b.burst
+	}
+	b.last = now
+	if b.tokens < 1 {
+		return false
+	}
+	b.tokens--
+	return true
+}
+
+type ipLimiter struct {
+	mu            sync.Mutex
+	buckets       map[string]*tokenBucket
+	ratePerMinute float64
+	burst         float64
+}
+
+func newIPLimiter(ratePerMinute, burst float64) *ipLimiter {
+	return &ipLimiter{buckets: map[string]*tokenBucket{}, ratePerMinute: ratePerMinute, burst: burst}
+}
+
+func (l *ipLimiter) Allow(r *http.Request) bool {
+	host, _, err := net.SplitHostPort(r.RemoteAddr)
+	if err != nil {
+		host = r.RemoteAddr
+	}
+	l.mu.Lock()
+	if len(l.buckets) > 1024 {
+		cutoff := time.Now().Add(-10 * time.Minute)
+		for addr, bucket := range l.buckets {
+			bucket.mu.Lock()
+			idle := bucket.last.Before(cutoff)
+			bucket.mu.Unlock()
+			if idle {
+				delete(l.buckets, addr)
+			}
+		}
+	}
+	bucket, ok := l.buckets[host]
+	if !ok {
+		bucket = newTokenBucket(l.ratePerMinute, l.burst)
+		l.buckets[host] = bucket
+	}
+	l.mu.Unlock()
+	return bucket.allow()
+}
+
+func rateLimited(limiter *ipLimiter, next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if !limiter.Allow(r) {
+			w.Header().Set("Retry-After", "60")
+			writeJSON(w, http.StatusTooManyRequests, errorResponse{
+				Error:     "too many requests, try again shortly",
+				RequestID: requestIDFrom(r.Context()),
+			})
+			return
+		}
+		next.ServeHTTP(w, r)
+	})
+}

coordinator/internal/userservice/transport/http/server.go

@@ -51,14 +51,14 @@ func NewServer(log *slog.Logger, uc UseCases, issuer auth.Issuer) http.Handler {
 	// Method-aware patterns (Go 1.22+): a GET to /register is a 405, not a match.
 	mux.HandleFunc("GET /health", h.handleHealth)
 	mux.HandleFunc("POST /register", h.handleRegister)
-	mux.HandleFunc("POST /login", h.handleLogin)
+	mux.Handle("POST /login", rateLimited(newIPLimiter(loginRatePerMinute, loginBurst), http.HandlerFunc(h.handleLogin)))
 	// /me proves a token round-trips; it sits behind JWT auth.
 	mux.Handle("GET /me", chain(http.HandlerFunc(h.handleMe), withJWT(issuer)))
 
 	// Worker keys: a user mints a long-lived key (JWT-protected), and a worker
 	// trades it for a short-lived JWT on the public exchange endpoint — the key
 	// itself is the credential there, so no prior token is required.
-	mux.HandleFunc("POST /worker-tokens/exchange", h.handleExchangeWorkerKey)
+	mux.Handle("POST /worker-tokens/exchange", rateLimited(newIPLimiter(exchangeRatePerMinute, exchangeBurst), http.HandlerFunc(h.handleExchangeWorkerKey)))
 	mux.Handle("POST /worker-keys", chain(http.HandlerFunc(h.handleCreateWorkerKey), withJWT(issuer)))
 	mux.Handle("GET /worker-keys", chain(http.HandlerFunc(h.handleListWorkerKeys), withJWT(issuer)))
 	mux.Handle("DELETE /worker-keys/{id}", chain(http.HandlerFunc(h.handleRevokeWorkerKey), withJWT(issuer)))

coordinator/internal/userservice/transport/http/server_test.go

@@ -479,3 +479,12 @@ func TestAdminListsUsersAndKeys(t *testing.T) {
 		t.Errorf("admin revoke unknown key: got %d, want 404", rec.Code)
 	}
 }
+
+func TestRegistrationDisabledEnv(t *testing.T) {
+	t.Setenv("USERSERVICE_DISABLE_REGISTRATION", "1")
+	h := newTestServer()
+	rec := do(t, h, http.MethodPost, "/register", "", map[string]string{"email": "blocked@x.io", "password": "pw"})
+	if rec.Code != http.StatusForbidden {
+		t.Errorf("register when disabled: got %d, want 403", rec.Code)
+	}
+}

install.ps1

@@ -8,6 +8,11 @@
 #   coordinator serve --open
 $ErrorActionPreference = "Stop"
 
+# Public half of the Ed25519 key that signs SHA256SUMS.txt in releases (see
+# install.sh). Verification needs the openssl binary; without it the installer
+# falls back to checksum verification with a warning.
+$ScimeshSigningPubKey = "MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA01rjmCme4W4zAgBwbO00LvwgnB1srlg0LbooRG8ej7iNxzOtJ8vjRFR2Cu7z7OKjoDo9/0GW3pvcwB+ndBB6yUwht33IRwdsnbioBI4M7LL+yC1ubi4fJ5bigOgZ9VsVqKdU3T9GYxmrfJF1UexiOg6HjoRLO3V4Id+3e/CiI5Sr8UMfJMXUfO3uiEs9RpstxpP1V/UU4YDicTF0QjkOESimEwwXBG4z3VcVmQtqkb7Q3413iekTdQ13093GKAKp0Q2ia1TpB2su6ELUhHAqhmK88cJ73Opy1uEVye0twov4BFTu5GkxgazNTuU//aYVWVpd/NAlD+VVSmpDsbfBBQIDAQAB"
+
 $Repo = "emil28092005/SciMesh"
 $Component = if ($env:SCIMESH_COMPONENT) { $env:SCIMESH_COMPONENT } else { "coordinator" }
 $Version = if ($env:SCIMESH_VERSION) { $env:SCIMESH_VERSION } else { "latest" }
@@ -57,6 +62,63 @@ $Target = Join-Path $InstallDir "$Binary.exe"
 
 Write-Host "Downloading $Url"
 Invoke-WebRequest -Uri $Url -OutFile "$Target.tmp"
+
+# Verify the SHA-256 checksum from the release before installing (see
+# install.sh for the caveats). $env:SCIMESH_SKIP_VERIFY -eq "1" bypasses.
+if ($env:SCIMESH_SKIP_VERIFY -ne "1") {
+    try {
+        $SumUrl = "https://github.com/$Repo/releases/download/$Version/SHA256SUMS.txt"
+
+        # Ed25519 signature over the checksum file, when openssl is present.
+        # Both files are fetched with -OutFile so their bytes match the
+        # release exactly (string pipelines would rewrite line endings).
+        $openssl = Get-Command openssl -ErrorAction SilentlyContinue
+        if ($env:SCIMESH_SKIP_SIGNATURE -ne "1" -and $openssl) {
+            $PubFile = Join-Path $env:TEMP "scimesh-signing-pub.pem"
+            $SumFile = Join-Path $env:TEMP ("scimesh-sums-" + [guid]::NewGuid().ToString("N") + ".txt")
+            $SigFile = "$SumFile.sig"
+            Set-Content -Path $PubFile -Value @("-----BEGIN PUBLIC KEY-----", $ScimeshSigningPubKey, "-----END PUBLIC KEY-----")
+            try {
+                Invoke-WebRequest -Uri $SumUrl -OutFile $SumFile
+                Invoke-WebRequest -Uri "$SumUrl.sig" -OutFile $SigFile
+                & $openssl.Source dgst -sha256 -verify $PubFile -signature $SigFile $SumFile 2>&1 | Out-Null
+                if ($LASTEXITCODE -eq 0) {
+                    Write-Host "Signature verified (RSA-2048/SHA-256)"
+                } else {
+                    Remove-Item -Force "$Target.tmp"
+                    throw "the release signature does not verify; the download channel may be tampered with"
+                }
+            } catch {
+                Remove-Item -Force "$Target.tmp"
+                throw "signature verification failed: $($_.Exception.Message)"
+            } finally {
+                Remove-Item -Force $PubFile, $SumFile, $SigFile -ErrorAction SilentlyContinue
+            }
+        } elseif ($env:SCIMESH_SKIP_SIGNATURE -ne "1") {
+            Write-Host "WARNING: openssl not found; falling back to checksum verification only"
+        }
+
+        $BinaryName = Split-Path $Url -Leaf
+        $SumFileCheck = Join-Path $env:TEMP ("scimesh-sums-check-" + [guid]::NewGuid().ToString("N") + ".txt")
+        Invoke-WebRequest -Uri $SumUrl -OutFile $SumFileCheck
+        $Line = (Get-Content $SumFileCheck -Raw -ErrorAction SilentlyContinue -split "`n") | Where-Object { $_.Trim().EndsWith("  " + $BinaryName) } | Select-Object -First 1
+        if ($Line) {
+            $Expected = ($Line -split "\s+")[0]
+            $Actual = (Get-FileHash -Algorithm SHA256 -Path "$Target.tmp").Hash.ToLower()
+            if ($Actual -ne $Expected.ToLower()) {
+                Remove-Item -Force "$Target.tmp", $SumFileCheck
+                throw "checksum mismatch for $Binary (got $Actual, want $Expected)"
+            }
+            Write-Host "Checksum verified ($($Expected.Substring(0,12))...)"
+        } else {
+            Write-Host "WARNING: no checksum entry for $Binary; skipping verification"
+            Remove-Item -Force $SumFileCheck -ErrorAction SilentlyContinue
+        }
+    } catch {
+        Write-Host "WARNING: could not verify checksum ($($_.Exception.Message)); continuing"
+    }
+}
+
 Move-Item -Force "$Target.tmp" $Target
 
 Write-Host ""

install.sh

@@ -14,6 +14,13 @@
 set -eu
 
 REPO="emil28092005/SciMesh"
+
+# Public half of the Ed25519 key that signs SHA256SUMS.txt in releases. The
+# private half lives in the repository secret SCIMESH_SIGNING_KEY. Verification
+# uses openssl when available; without openssl the installer falls back to the
+# checksum-only check with a warning.
+SCIMESH_SIGNING_PUBKEY='MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA01rjmCme4W4zAgBwbO00LvwgnB1srlg0LbooRG8ej7iNxzOtJ8vjRFR2Cu7z7OKjoDo9/0GW3pvcwB+ndBB6yUwht33IRwdsnbioBI4M7LL+yC1ubi4fJ5bigOgZ9VsVqKdU3T9GYxmrfJF1UexiOg6HjoRLO3V4Id+3e/CiI5Sr8UMfJMXUfO3uiEs9RpstxpP1V/UU4YDicTF0QjkOESimEwwXBG4z3VcVmQtqkb7Q3413iekTdQ13093GKAKp0Q2ia1TpB2su6ELUhHAqhmK88cJ73Opy1uEVye0twov4BFTu5GkxgazNTuU//aYVWVpd/NAlD+VVSmpDsbfBBQIDAQAB'
+
 COMPONENT="${1:-coordinator}"
 VERSION="${SCIMESH_VERSION:-latest}"
 INSTALL_DIR="${SCIMESH_INSTALL_DIR:-$HOME/.local/bin}"
@@ -60,6 +67,50 @@ TARGET="$INSTALL_DIR/$BINARY"
 URL="https://github.com/${REPO}/releases/download/${VERSION}/${BINARY}-${OS}-${ARCH}"
 echo "Downloading $URL"
 curl -fsSL -o "$TARGET.tmp" "$URL"
+
+# Verify the SHA-256 checksum from the release before installing. This guards
+# against corrupted downloads and stale CDN caches; it does not protect
+# against an active MITM on the same channel (the checksum file travels it
+# too). Set SCIMESH_SKIP_VERIFY=1 to bypass.
+if [ "${SCIMESH_SKIP_VERIFY:-0}" != "1" ]; then
+  if SUMFILE=$(mktemp) && curl -fsSL -o "$SUMFILE" "https://github.com/${REPO}/releases/download/${VERSION}/SHA256SUMS.txt"; then
+    EXPECTED=$(awk '$2 == "'"$(basename "$URL")"'" {print $1}' "$SUMFILE" 2>/dev/null | head -1)
+    SIGFILE="$SUMFILE.sig"
+    if [ "${SCIMESH_SKIP_SIGNATURE:-0}" != "1" ] && command -v openssl >/dev/null 2>&1 \
+        && curl -fsSL -o "$SIGFILE" "https://github.com/${REPO}/releases/download/${VERSION}/SHA256SUMS.txt.sig" 2>/dev/null; then
+      PUBKEY_FILE=$(mktemp)
+      printf '%s\n' '-----BEGIN PUBLIC KEY-----' "$SCIMESH_SIGNING_PUBKEY" '-----END PUBLIC KEY-----' > "$PUBKEY_FILE"
+      if openssl dgst -sha256 -verify "$PUBKEY_FILE" -signature "$SIGFILE" "$SUMFILE" >/dev/null 2>&1; then
+        echo "Signature verified (RSA-2048/SHA-256)"
+      else
+        rm -f "$PUBKEY_FILE" "$SIGFILE" "$SUMFILE" "$TARGET.tmp"
+        echo "ERROR: the release signature does not verify; the download channel may be tampered with." >&2
+        echo "Retry later, or bypass with SCIMESH_SKIP_SIGNATURE=1." >&2
+        exit 1
+      fi
+      rm -f "$PUBKEY_FILE"
+    elif [ "${SCIMESH_SKIP_SIGNATURE:-0}" != "1" ] && ! command -v openssl >/dev/null 2>&1; then
+      echo "WARNING: openssl not found; falling back to checksum verification only"
+    fi
+    rm -f "$SUMFILE" "$SIGFILE"
+    if [ -n "$EXPECTED" ]; then
+      ACTUAL=$(sha256sum "$TARGET.tmp" | awk '{print $1}')
+      if [ "$ACTUAL" != "$EXPECTED" ]; then
+        rm -f "$TARGET.tmp"
+        echo "ERROR: checksum mismatch for $BINARY (got $ACTUAL, want $EXPECTED)" >&2
+        echo "The download may be corrupted or served by a stale cache. Retry later, or" >&2
+        echo "pin the version with SCIMESH_VERSION=${VERSION} and re-run." >&2
+        exit 1
+      fi
+      echo "Checksum verified ($(echo "$EXPECTED" | cut -c1-12)…)"
+    else
+      echo "WARNING: no checksum entry for $(basename "$URL"); skipping verification"
+    fi
+  else
+    echo "WARNING: could not fetch SHA256SUMS.txt; skipping verification"
+  fi
+fi
+
 chmod +x "$TARGET.tmp"
 mv "$TARGET.tmp" "$TARGET"