diff --git a/cmds/portmaster-start/main.go b/cmds/portmaster-start/main.go
index 96801174..3a58d596 100644
--- a/cmds/portmaster-start/main.go
+++ b/cmds/portmaster-start/main.go
@@ -34,12 +34,9 @@ var (
 		UpdateURLs: []string{
 			"https://updates.safing.io",
 		},
-		Verification: helper.VerificationConfig,
-		// FIXME: Add:
-		// integrity check: pretty much the same as "jess verify"
-		// integrity fix: same as check, but delete broken stuff and download again
-		DevMode: false,
-		Online:  true, // is disabled later based on command
+		Verification: helper.VerificationConfig, // FIXME: disable for now
+		DevMode:      false,
+		Online:       true, // is disabled later based on command
 	}
 
 	rootCmd = &cobra.Command{
diff --git a/cmds/portmaster-start/verify.go b/cmds/portmaster-start/verify.go
new file mode 100644
index 00000000..798485db
--- /dev/null
+++ b/cmds/portmaster-start/verify.go
@@ -0,0 +1,142 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"os"
+	"strings"
+
+	"github.com/spf13/cobra"
+
+	"github.com/safing/jess"
+	"github.com/safing/jess/filesig"
+	"github.com/safing/portbase/updater"
+)
+
+var (
+	verifyVerbose bool
+	verifyFix     bool
+
+	verifyCmd = &cobra.Command{
+		Use:   "verify",
+		Short: "Check integrity of updates / components",
+		RunE: func(cmd *cobra.Command, args []string) error {
+			return verifyUpdates(cmd.Context())
+		},
+	}
+)
+
+func init() {
+	rootCmd.AddCommand(verifyCmd)
+
+	flags := verifyCmd.Flags()
+	flags.BoolVarP(&verifyVerbose, "verbose", "v", false, "Enable verbose output")
+	flags.BoolVar(&verifyFix, "fix", false, "Delete and re-download broken components")
+}
+
+func verifyUpdates(ctx context.Context) error {
+	// Force registry to require signatures for all enabled scopes.
+	for _, opts := range registry.Verification {
+		if opts != nil {
+			opts.DownloadPolicy = updater.SignaturePolicyRequire
+			opts.DiskLoadPolicy = updater.SignaturePolicyRequire
+		}
+	}
+
+	// Load indexes again to ensure they are correctly signed.
+	err := registry.LoadIndexes(ctx)
+	if err != nil {
+		if verifyFix {
+			log.Println("[WARN] loading indexes failed, re-downloading...")
+			err = registry.UpdateIndexes(ctx)
+			if err != nil {
+				return fmt.Errorf("failed to download indexes: %w", err)
+			}
+			log.Println("[ OK ] indexes re-downloaded and verified")
+		} else {
+			return fmt.Errorf("failed to verify indexes: %w", err)
+		}
+	} else {
+		log.Println("[ OK ] indexes verified")
+	}
+
+	// Verify all resources.
+	export := registry.Export()
+	var verified, fails int
+	for _, rv := range export {
+		for _, version := range rv.Versions {
+			file := version.GetFile()
+
+			// Verify file signature.
+			fileData, err := file.Verify()
+			if err != nil {
+				log.Printf("[FAIL] failed to verify %s: %s\n", file.Path(), err)
+				fails++
+				if verifyFix {
+					// Delete file.
+					err = os.Remove(file.Path())
+					if err != nil {
+						log.Printf("[FAIL] failed to delete %s to prepare re-download: %s\n", file.Path(), err)
+					}
+					// Delete file sig.
+					err = os.Remove(file.Path() + filesig.Extension)
+					if err != nil {
+						log.Printf("[FAIL] failed to delete %s to prepare re-download: %s\n", file.Path()+filesig.Extension, err)
+					}
+				}
+			} else {
+				if verifyVerbose {
+					verifOpts := registry.GetVerificationOptions(file.Identifier())
+					if verifOpts != nil {
+						log.Printf(
+							"[ OK ] valid signature for %s: signed by %s\n",
+							file.Path(), getSignedByMany(fileData, verifOpts.TrustStore),
+						)
+					} else {
+						log.Printf("[ OK ] valid signature for %s\n", file.Path())
+					}
+				}
+				verified++
+			}
+		}
+	}
+
+	if verified > 0 {
+		log.Printf("[STAT] verified %d files\n", verified)
+	}
+	if fails > 0 {
+		if verifyFix {
+			log.Printf("[WARN] verification failed %d files, re-downloading...\n", fails)
+		} else {
+			return fmt.Errorf("failed to verify %d files", fails)
+		}
+	} else {
+		// Everything was verified!
+		return nil
+	}
+
+	// Re-download broken files.
+	err = registry.DownloadUpdates(ctx)
+	if err != nil {
+		return fmt.Errorf("failed to re-download files: %w", err)
+	}
+
+	return nil
+}
+
+func getSignedByMany(fds []*filesig.FileData, trustStore jess.TrustStore) string {
+	signedBy := make([]string, 0, len(fds))
+	for _, fd := range fds {
+		if sig := fd.Signature(); sig != nil {
+			for _, seal := range sig.Signatures {
+				if signet, err := trustStore.GetSignet(seal.ID, true); err == nil {
+					signedBy = append(signedBy, fmt.Sprintf("%s (%s)", signet.Info.Name, seal.ID))
+				} else {
+					signedBy = append(signedBy, seal.ID)
+				}
+			}
+		}
+	}
+	return strings.Join(signedBy, " and ")
+}