Say plainly when the private key cannot decrypt a snapshot (closes #427)

Restore and deep verify now report "cannot decrypt this snapshot: the
private key in VAULTIK_AGE_SECRET_KEY is not one of the keys the backup
was encrypted to", naming the key source like the invalid-key error.
The doubled "creating decryption reader" prefix and the outer
"downloading snapshot database" / "failed to decrypt database" prefixes
are gone for this case.

A blob the key cannot decrypt, such as one stored before the key was
added as a recipient, now reports "cannot decrypt this blob: the
private key in VAULTIK_AGE_SECRET_KEY is not one of the keys the blob
was encrypted to" after the file and blob it belongs to.

Model: opus-5-5

README.md

@@ -831,8 +831,7 @@ Work planned after 1.0. Loosely ordered by priority.
 
 Every command's user-facing output is governed by `internal/ui`, in one of two
 ways. Color is enabled when the stream written to is a TTY and the `NO_COLOR`
-environment variable is unset (https://no-color.org/). The same rule governs the
-colorized log lines `internal/log` writes to a terminal.
+environment variable is unset (https://no-color.org/).
 
 - **Status, progress, warnings, and errors** go through the `internal/ui`
   message methods below: marker-prefixed, colored on a TTY, and — except

internal/log/tty_handler.go

@@ -5,7 +5,6 @@ import (
 	"fmt"
 	"io"
 	"log/slog"
-	"os"
 	"strconv"
 	"strings"
 	"sync"
@@ -61,12 +60,6 @@ type TTYHandler struct {
 	mu   *sync.Mutex
 	out  io.Writer
 
-	// color reports whether records are written with ANSI color. It is
-	// false when NO_COLOR is set, matching internal/ui's shouldColor
-	// test; the caller already chose this handler for a terminal, so
-	// TTY-ness is not re-checked here.
-	color bool
-
 	// attrs are the attributes accumulated through WithAttrs, emitted
 	// ahead of each record's own attributes. Their keys already carry
 	// the group path that was open when they were added, so no
@@ -79,19 +72,16 @@ type TTYHandler struct {
 	groups []string
 }
 
-// NewTTYHandler creates a new TTY handler. Color is enabled unless the
-// NO_COLOR environment variable is set to a non-empty value, the same
-// test internal/ui applies to status lines.
+// NewTTYHandler creates a new TTY handler with colored output.
 func NewTTYHandler(out io.Writer, opts *slog.HandlerOptions) *TTYHandler {
 	if opts == nil {
 		opts = &slog.HandlerOptions{}
 	}
 
 	return &TTYHandler{
-		out:   out,
-		opts:  *opts,
-		mu:    &sync.Mutex{},
-		color: os.Getenv("NO_COLOR") == "",
+		out:  out,
+		opts: *opts,
+		mu:   &sync.Mutex{},
 	}
 }
 
@@ -134,10 +124,10 @@ func (h *TTYHandler) Handle(_ context.Context, r slog.Record) error {
 	// are written around it: it can carry text from an untrusted source
 	// (a storage error, for one), and a raw control character would
 	// otherwise reach the terminal.
-	_, _ = fmt.Fprintf(h.out, "%s %s %s",
-		h.paint(colorGray, timestamp),
-		h.paint(levelColor, level),
-		h.paint(colorBold, sanitize(r.Message)))
+	_, _ = fmt.Fprintf(h.out, "%s%s%s %s%s%s %s%s%s",
+		colorGray, timestamp, colorReset,
+		levelColor, level, colorReset,
+		colorBold, sanitize(r.Message), colorReset)
 
 	// Attributes carried by the handler come first, then the record's
 	// own. Handler attributes were qualified when they were added; the
@@ -246,7 +236,6 @@ func (h *TTYHandler) clone() *TTYHandler {
 		opts:   h.opts,
 		mu:     h.mu,
 		out:    h.out,
-		color:  h.color,
 		attrs:  make([]slog.Attr, len(h.attrs), len(h.attrs)+1),
 		groups: make([]string, len(h.groups), len(h.groups)+1),
 	}
@@ -284,19 +273,9 @@ func (h *TTYHandler) writeAttr(a slog.Attr) {
 	// the snapshot database — so a control character in one of them must
 	// be rendered as an escape sequence rather than reaching the terminal,
 	// where it could move the cursor or inject its own colours.
-	_, _ = fmt.Fprintf(h.out, " %s=%s",
-		h.paint(colorCyan, sanitize(a.Key)),
-		h.paint(colorBlue, sanitize(value)))
-}
-
-// paint wraps s in the given ANSI color when color is enabled, and
-// returns s unchanged otherwise.
-func (h *TTYHandler) paint(color, s string) string {
-	if !h.color {
-		return s
-	}
-
-	return color + s + colorReset
+	_, _ = fmt.Fprintf(h.out, " %s%s%s=%s%s%s",
+		colorCyan, sanitize(a.Key), colorReset,
+		colorBlue, sanitize(value), colorReset)
 }
 
 // sanitize returns s unchanged when every rune in it is printable, and a

internal/log/tty_handler_test.go

@@ -421,44 +421,3 @@ func TestTTYHandlerEmptyGroupAndAttrsAreNoOps(t *testing.T) {
 	assert.Contains(t, plain, "kept=yes")
 	assert.NotContains(t, plain, " =")
 }
-
-// TestTTYHandlerRespectsNoColor checks that only a non-empty NO_COLOR
-// turns color off, matching internal/ui's shouldColor test. The handler
-// is only ever chosen for a terminal, so this is the one remaining
-// condition that can still leave color in log output.
-func TestTTYHandlerRespectsNoColor(t *testing.T) {
-	cases := []struct {
-		name    string
-		noColor string
-		colored bool
-	}{
-		{
-			name:    "NO_COLOR turns color off",
-			noColor: "1",
-		},
-		{
-			name:    "empty NO_COLOR keeps color on",
-			noColor: "",
-			colored: true,
-		},
-	}
-
-	for _, testCase := range cases {
-		t.Run(testCase.name, func(t *testing.T) {
-			t.Setenv("NO_COLOR", testCase.noColor)
-
-			var buf bytes.Buffer
-
-			logger := slog.New(log.NewTTYHandler(&buf, debugHandlerOptions()))
-			logger.Info("hello", "key", "value")
-
-			if testCase.colored {
-				assert.Contains(t, buf.String(), "\x1b[",
-					"an empty NO_COLOR must leave ANSI color in log output")
-			} else {
-				assert.NotContains(t, buf.String(), "\x1b[",
-					"NO_COLOR must suppress every ANSI escape in log output")
-			}
-		})
-	}
-}

internal/vaultik/blob_fetch.go

@@ -22,6 +22,10 @@ var errBlobHashMismatch = errors.New("blob hash mismatch")
 var errBlobNotFullyRead = errors.New(
 	"blob closed before fully read; hash not verified")
 
+// errWrongPrivateKeyForBlob is returned when the configured key parses
+// but is not one of the keys a blob was encrypted to.
+var errWrongPrivateKeyForBlob = errors.New("cannot decrypt this blob")
+
 // hashVerifyReader wraps a blobgen.Reader and verifies the double-SHA-256 hash
 // of decrypted plaintext when Close is called. It reuses the hash that
 // blobgen.Reader already computes internally via its TeeReader, avoiding
@@ -87,10 +91,14 @@ func (v *Vaultik) FetchAndDecryptBlob(
 		return nil, err
 	}
 
-	reader, err := blobgen.NewReader(rc, identities...)
+	reader, err := v.newBlobReader(rc, identities)
 	if err != nil {
 		_ = rc.Close()
 
+		if errors.Is(err, errWrongPrivateKeyForBlob) {
+			return nil, err
+		}
+
 		return nil, fmt.Errorf("creating blob reader: %w", err)
 	}
 
@@ -102,6 +110,28 @@ func (v *Vaultik) FetchAndDecryptBlob(
 	}, nil
 }
 
+// newBlobReader opens the decrypting reader for a blob. When none of the
+// identities can decrypt it, the error says in plain words that the
+// configured private key is not one of the keys the blob was encrypted
+// to and names where the key was configured.
+func (v *Vaultik) newBlobReader(
+	r io.Reader, identities []age.Identity,
+) (*blobgen.Reader, error) {
+	blobReader, err := blobgen.NewReader(r, identities...)
+
+	if _, ok := errors.AsType[*age.NoIdentityMatchError](err); ok {
+		return nil, fmt.Errorf(
+			"%w: the private key in %s is not one of the keys the blob was encrypted to",
+			errWrongPrivateKeyForBlob, v.Config.AgeSecretKeySourceName())
+	}
+
+	if err != nil {
+		return nil, err
+	}
+
+	return blobReader, nil
+}
+
 // FetchBlob downloads a blob and returns a reader for the encrypted data.
 // The reader is closed as soon as ctx is cancelled, which ends a read
 // blocked inside it. A storage error is returned as is: restore and deep

internal/vaultik/missing_destination_test.go

@@ -7,6 +7,7 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
+	"sync"
 	"testing"
 
 	"github.com/spf13/afero"
@@ -24,19 +25,28 @@ import (
 // that is not plugged in, cannot be listed. It is not an empty store, so
 // no command may conclude from it that the local snapshots are gone.
 
-// newFileDestinationVaultik returns a Vaultik that backs up the
-// snapshot named "first" to a file:// destination at storeDir.
+// newFileDestinationVaultik writes the fault source tree and returns a
+// Vaultik that backs it up to a file:// destination at storeDir.
 func newFileDestinationVaultik(
 	ctx context.Context, t *testing.T, storeDir string,
 ) (*vaultik.Vaultik, *database.Repositories) {
 	t.Helper()
 
-	osFs := afero.NewOsFs()
 	tempDir := t.TempDir()
 	dataDir := filepath.Join(tempDir, "src")
-	dbPath := filepath.Join(tempDir, "index.sqlite")
+	writeFaultSourceTree(t, afero.NewOsFs(), dataDir)
 
-	writeFaultSourceTree(t, osFs, dataDir)
+	return openFileDestinationVaultik(ctx, t, storeDir, dataDir,
+		filepath.Join(tempDir, "index.sqlite"))
+}
+
+// openFileDestinationVaultik returns a Vaultik that backs up dataDir to a
+// file:// destination at storeDir, with its local index at dbPath. The
+// index is closed when the test ends.
+func openFileDestinationVaultik(
+	ctx context.Context, t *testing.T, storeDir, dataDir, dbPath string,
+) (*vaultik.Vaultik, *database.Repositories) {
+	t.Helper()
 
 	store, err := storage.NewFileStorer(storeDir)
 	require.NoError(t, err)
@@ -48,22 +58,84 @@ func newFileDestinationVaultik(
 	repos := database.NewRepositories(db)
 	cfg := changedFileConfig(dataDir, dbPath)
 
-	return newBackupVaultik(ctx, cfg, store, repos, db, osFs), repos
+	return newBackupVaultik(ctx, cfg, store, repos, db, afero.NewOsFs()), repos
+}
+
+// firstBackup is one backup of the snapshot named "first" to a file://
+// destination. dir holds its source tree in src, its store in store and
+// its closed local index in index/index.sqlite. The first test that
+// needs it makes it, and TestMain removes it. Every test that copies it
+// backs up the same source tree, so no test may change that tree.
+//
+//nolint:gochecknoglobals // made once and shared by the tests that copy it
+var firstBackup struct {
+	once  sync.Once
+	dir   string
+	ready bool
+}
+
+// TestMain removes firstBackup once every test has run.
+func TestMain(m *testing.M) {
+	code := m.Run()
+
+	_ = os.RemoveAll(firstBackup.dir)
+
+	os.Exit(code)
+}
+
+// makeFirstBackup writes the fault source tree and backs it up as the
+// snapshot named "first", all in a new directory that it records in
+// firstBackup.
+func makeFirstBackup(ctx context.Context, t *testing.T) {
+	t.Helper()
+
+	dir, err := os.MkdirTemp("", "vaultik-first-backup-")
+	require.NoError(t, err)
+
+	firstBackup.dir = dir
+	storeDir := filepath.Join(dir, "store")
+	dataDir := filepath.Join(dir, "src")
+	indexDir := filepath.Join(dir, "index")
+
+	require.NoError(t, os.Mkdir(storeDir, 0o750))
+	require.NoError(t, os.Mkdir(indexDir, 0o750))
+	writeFaultSourceTree(t, afero.NewOsFs(), dataDir)
+
+	v, _ := openFileDestinationVaultik(ctx, t, storeDir, dataDir,
+		filepath.Join(indexDir, "index.sqlite"))
+	require.NoError(t, backUp(v, "first"))
+	require.NoError(t, v.DB.Close())
+
+	firstBackup.ready = true
 }
 
 // backUpToFileDestination creates the directory storeDir, as a user must
-// before the first backup, and backs up the snapshot named "first" to a
-// file:// destination there. Everything the returned Vaultik prints
-// after the backup goes to the returned buffer.
+// before the first backup, and returns a Vaultik whose file://
+// destination there holds a backup of the snapshot named "first". The
+// store and the local index are copies of firstBackup's, which is faster
+// than backing up in every test. The returned Vaultik backs up a source
+// tree shared with every other caller, so no test may change that tree.
+// Everything the returned Vaultik prints after the backup goes to the
+// returned buffer.
 func backUpToFileDestination(
 	ctx context.Context, t *testing.T, storeDir string,
 ) (*vaultik.Vaultik, *database.Repositories, *bytes.Buffer) {
 	t.Helper()
 
-	require.NoError(t, os.MkdirAll(storeDir, 0o750))
+	firstBackup.once.Do(func() { makeFirstBackup(ctx, t) })
+	require.True(t, firstBackup.ready, "another test failed to make firstBackup")
 
-	v, repos := newFileDestinationVaultik(ctx, t, storeDir)
-	require.NoError(t, backUp(v, "first"))
+	require.NoError(t, os.MkdirAll(storeDir, 0o750))
+	require.NoError(t, os.CopyFS(storeDir,
+		os.DirFS(filepath.Join(firstBackup.dir, "store"))))
+
+	indexDir := t.TempDir()
+	require.NoError(t, os.CopyFS(indexDir,
+		os.DirFS(filepath.Join(firstBackup.dir, "index"))))
+
+	v, repos := openFileDestinationVaultik(ctx, t, storeDir,
+		filepath.Join(firstBackup.dir, "src"),
+		filepath.Join(indexDir, "index.sqlite"))
 
 	out := &bytes.Buffer{}
 	v.Stdout = out

internal/vaultik/restore.go

@@ -40,6 +40,9 @@ var (
 	// which is secret, so the message is safe to print and log.
 	errInvalidAgeSecretKey = errors.New(
 		"configured age secret key holds no usable age identity")
+	// errWrongPrivateKey is returned when the configured key parses but
+	// is not one of the keys the snapshot was encrypted to.
+	errWrongPrivateKey          = errors.New("cannot decrypt this snapshot")
 	errBlobMissingFromIndex     = errors.New("blob hash missing from blob index")
 	errChunkNotInAnyBlob        = errors.New("chunk not found in any blob")
 	errBlobIDNotInHashIndex     = errors.New("blob id missing from hash index")
@@ -132,6 +135,10 @@ func (v *Vaultik) Restore(opts *RestoreOptions) error {
 	log.Info("Downloading snapshot metadata...")
 
 	tempDB, tempDir, err := v.downloadSnapshotDB(opts.SnapshotID, identities)
+	if errors.Is(err, errWrongPrivateKey) {
+		return err
+	}
+
 	if err != nil {
 		return fmt.Errorf("downloading snapshot database: %w", err)
 	}
@@ -323,6 +330,28 @@ func (v *Vaultik) restoreIdentities() ([]age.Identity, error) {
 	return identities, nil
 }
 
+// newSnapshotDBReader opens the decrypting reader for a snapshot
+// database. When none of the identities can decrypt it, the error says
+// in plain words that the configured private key is the wrong one and
+// names where it was configured.
+func (v *Vaultik) newSnapshotDBReader(
+	r io.Reader, identities []age.Identity,
+) (*blobgen.Reader, error) {
+	blobReader, err := blobgen.NewReader(r, identities...)
+
+	if _, ok := errors.AsType[*age.NoIdentityMatchError](err); ok {
+		return nil, fmt.Errorf(
+			"%w: the private key in %s is not one of the keys the backup was encrypted to",
+			errWrongPrivateKey, v.Config.AgeSecretKeySourceName())
+	}
+
+	if err != nil {
+		return nil, err
+	}
+
+	return blobReader, nil
+}
+
 // restoreAllFiles processes files in blob-locality order: drain every
 // file whose blob set is on disk, download the missing blobs for the
 // pending file with the smallest uncached count, repeat. This keeps
@@ -783,9 +812,9 @@ func (v *Vaultik) downloadSnapshotDB(
 	// the plaintext to a temp file. Neither the encrypted bytes nor the
 	// decrypted database is ever held whole in memory; a snapshot database
 	// can be large.
-	blobReader, err := blobgen.NewReader(reader, identities...)
+	blobReader, err := v.newSnapshotDBReader(reader, identities)
 	if err != nil {
-		return nil, "", fmt.Errorf("creating decryption reader: %w", err)
+		return nil, "", err
 	}
 
 	defer func() { _ = blobReader.Close() }()

internal/vaultik/restore_locality_test.go

@@ -46,11 +46,11 @@ import (
 //     slice out a few KB — currently the dominant cost in restore.
 //
 // The test deliberately constructs an adversarial scenario: three
-// blobs A/B/C of ~6 MB each, nine files distributed across them, and
-// path-ordered names that interleave the blobs (a1, b1, c1, a2, b2,
-// c2, …) so naive path-order processing would touch every blob before
-// finishing any of them.
-// localitySource is one 1 MiB fixture file used by the locality test.
+// blobs A/B/C of five 64 KiB chunks each, nine files distributed across
+// them, and path-ordered names that interleave the blobs (a1, b1, c1,
+// a2, b2, c2, …) so naive path-order processing would touch every blob
+// before finishing any of them.
+// localitySource is one 64 KiB fixture file used by the locality test.
 type localitySource struct {
 	path string
 	data []byte
@@ -65,10 +65,10 @@ type localityCopy struct {
 
 // localitySourceBytes is the size of each source file of the locality
 // fixture.
-const localitySourceBytes = 1024 * 1024
+const localitySourceBytes = 64 * 1024
 
 // buildLocalityFixture writes the adversarial source layout described
-// in TestRestoreLocalityAndReadAt: 15 sources of 1 MiB each (which the
+// in TestRestoreLocalityAndReadAt: 15 sources of 64 KiB each (which the
 // backup packs into 3 blobs of 5 chunks) plus 9 interleaved-name copies
 // (3 per blob group).
 func buildLocalityFixture(

internal/vaultik/restore_sweeper_integration_test.go

@@ -27,10 +27,10 @@ import (
 // TestRestoreSweeperEvictsBlobs exercises the reference-counted blob
 // disk cache eviction during restore.
 //
-// The scenario: 30 unique 1 MB random files plus 10 duplicates of those
-// (40 files total, 30 MB of unique content) get backed up with a 10 MB
-// blob_size_limit. After backup the snapshot's encrypted blobs are
-// restored through Vaultik.Restore, and per-key Get counts on the
+// The scenario: 30 unique 128 KiB random files plus 10 duplicates of
+// those (40 files total, 3.75 MiB of unique content) get backed up with
+// a 1 MiB blob_size_limit. After backup the snapshot's encrypted blobs
+// are restored through Vaultik.Restore, and per-key Get counts on the
 // storage layer are recorded. Each blob in the snapshot MUST be
 // downloaded exactly once — re-downloads would mean the sweeper either
 // evicted a blob that was still needed (LRU regression) or that the
@@ -41,7 +41,7 @@ import (
 // original AND every duplicate referencing its chunks have been
 // restored.
 // buildSweeperFixture writes the source layout for the sweeper test: 30
-// unique 1 MB random files plus 10 duplicates of a random subset. The
+// unique 128 KiB random files plus 10 duplicates of a random subset. The
 // PRNG seed is fixed so failures are reproducible; the entropy is what
 // matters here — the FastCDC chunker needs realistic-looking data to
 // pick chunk boundaries naturally. Returns the expected content by
@@ -51,7 +51,7 @@ func buildSweeperFixture(
 ) map[string][]byte {
 	t.Helper()
 
-	const fileSize = 1 * 1024 * 1024
+	const fileSize = 128 * 1024
 
 	rng := rand.New(rand.NewSource(42)) //nolint:gosec // G404: fixture data only
 
@@ -159,7 +159,7 @@ func runSweeperBackup(
 	require.NoError(t, err)
 	require.Equal(t, uniqueFiles+duplicateFiles, scanResult.FilesScanned)
 	require.Greater(t, scanResult.BlobsCreated, 1,
-		"30 MB of unique data at 10 MB blob size should yield multiple blobs")
+		"3.75 MiB of unique data at 1 MiB blob size should yield multiple blobs")
 
 	require.NoError(t, sm.CompleteSnapshot(ctx, snapshotID))
 	require.NoError(t, sm.ExportSnapshotMetadata(ctx, dbPath, snapshotID))
@@ -199,8 +199,8 @@ func TestRestoreSweeperEvictsBlobs(t *testing.T) {
 
 	expected := buildSweeperFixture(t, fs, dataDir, uniqueFiles, duplicateFiles)
 
-	chunkSize := int64(64 * 1024)
-	maxBlobSize := int64(10 * 1024 * 1024)
+	chunkSize := int64(16 * 1024)
+	maxBlobSize := int64(1024 * 1024)
 
 	storer, err := storage.NewFileStorer(storeDir)
 	require.NoError(t, err)

internal/vaultik/restore_wrong_key_test.go

@@ -0,0 +1,161 @@
+package vaultik_test
+
+import (
+	"bytes"
+	"context"
+	"io"
+	"path"
+	"path/filepath"
+	"testing"
+
+	"filippo.io/age"
+	"github.com/spf13/afero"
+	"github.com/stretchr/testify/require"
+	"sneak.berlin/go/vaultik/internal/blobgen"
+	"sneak.berlin/go/vaultik/internal/config"
+	"sneak.berlin/go/vaultik/internal/log"
+	"sneak.berlin/go/vaultik/internal/snapshot"
+	"sneak.berlin/go/vaultik/internal/ui"
+	"sneak.berlin/go/vaultik/internal/vaultik"
+)
+
+// TestWrongPrivateKeyError checks that restore and deep verify, given a
+// valid private key the backup was not encrypted to, fail with one plain
+// sentence that names where the key was configured.
+func TestWrongPrivateKeyError(t *testing.T) {
+	t.Parallel()
+
+	ctx := context.Background()
+	store := NewMockStorer()
+
+	const snapshotID = "test-host_2026-01-01T00:00:00Z"
+
+	remoteKey := snapshot.RemoteSnapshotKey(snapshotID)
+
+	manifest, err := snapshot.EncodeManifest(
+		&snapshot.Manifest{SnapshotID: remoteKey}, 3)
+	require.NoError(t, err)
+	require.NoError(t, store.Put(ctx,
+		"metadata/"+remoteKey+"/manifest.json.zst", bytes.NewReader(manifest)))
+
+	// The database is encrypted to the test recipient only.
+	var db bytes.Buffer
+
+	writer, err := blobgen.NewWriter(&db, 1, []string{testAgePublicKey})
+	require.NoError(t, err)
+
+	_, err = writer.Write([]byte("snapshot database"))
+	require.NoError(t, err)
+	require.NoError(t, writer.Close())
+	require.NoError(t, store.Put(ctx,
+		"metadata/"+remoteKey+"/db.zst.age", &db))
+
+	otherKey, err := age.GenerateX25519Identity()
+	require.NoError(t, err)
+
+	v := &vaultik.Vaultik{
+		Config:  &config.Config{AgeSecretKey: otherKey.String()},
+		Storage: store,
+		Fs:      afero.NewMemMapFs(),
+		Stdout:  io.Discard,
+		Stderr:  io.Discard,
+		UI:      ui.NewWithColor(io.Discard, false),
+	}
+	v.SetContext(ctx)
+
+	// A Config built directly has no recorded source, so the error names
+	// the config-file field.
+	const want = "cannot decrypt this snapshot: the private key in " +
+		"age_secret_key is not one of the keys the backup was encrypted to"
+
+	err = v.Restore(&vaultik.RestoreOptions{
+		SnapshotID: snapshotID,
+		TargetDir:  t.TempDir(),
+	})
+	require.EqualError(t, err, want)
+
+	err = v.RunDeepVerify(snapshotID, &vaultik.VerifyOptions{Deep: true})
+	require.EqualError(t, err, want)
+}
+
+// TestWrongPrivateKeyForBlobError backs up a file, then backs it up again
+// from an empty local index with a second recipient added. The second
+// snapshot reuses the stored blob, which stays encrypted to the first
+// recipient only. With only the added key configured, restore and deep
+// verify read the database but fail on the blob with one plain sentence
+// that names where the key was configured.
+func TestWrongPrivateKeyForBlobError(t *testing.T) {
+	log.Initialize(log.Config{})
+	t.Parallel()
+
+	fs := afero.NewOsFs()
+	tempDir := t.TempDir()
+	dataDir := filepath.Join(tempDir, "source")
+	dataPath := filepath.Join(dataDir, "data.bin")
+	storeDir := t.TempDir()
+	secondDBPath := filepath.Join(tempDir, "second.sqlite")
+
+	chunkSize := int64(64 * 1024)
+	maxBlobSize := int64(512 * 1024)
+
+	require.NoError(t, fs.MkdirAll(dataDir, 0o755))
+	require.NoError(t, afero.WriteFile(fs, dataPath,
+		bytesPattern("key-", int(chunkSize)), 0o644))
+
+	ctx := context.Background()
+
+	runFileStorageBackup(ctx, t, fs, dataDir, storeDir,
+		filepath.Join(tempDir, "first.sqlite"), chunkSize, maxBlobSize)
+
+	env := setupDedupBackupEnv(
+		ctx, t, fs, storeDir, secondDBPath, chunkSize, maxBlobSize)
+
+	defer func() { _ = env.db.Close() }()
+
+	addedKey, err := age.GenerateX25519Identity()
+	require.NoError(t, err)
+
+	env.cfg.AgeRecipients = append(env.cfg.AgeRecipients,
+		addedKey.Recipient().String())
+
+	snapshotID, result := runDedupSnapshot(ctx, t, env.sm, env.makeScanner(),
+		env.cfg.Hostname, "second", dataDir, secondDBPath)
+	require.Zero(t, result.BlobsUploaded,
+		"the second backup should reuse the stored blob")
+
+	require.NoError(t, env.db.Close())
+
+	blobKeys, err := env.storer.List(ctx, "blobs/")
+	require.NoError(t, err)
+	require.Len(t, blobKeys, 1)
+
+	blobHash := path.Base(blobKeys[0])
+
+	env.cfg.AgeSecretKey = addedKey.String()
+
+	v := &vaultik.Vaultik{
+		Config:  env.cfg,
+		Storage: env.storer,
+		Fs:      fs,
+		Stdout:  io.Discard,
+		Stderr:  io.Discard,
+		UI:      ui.NewWithColor(io.Discard, false),
+	}
+	v.SetContext(ctx)
+
+	const sentence = "cannot decrypt this blob: the private key in " +
+		"age_secret_key is not one of the keys the blob was encrypted to"
+
+	// Restore names the blob by the first 16 characters of its hash.
+	err = v.Restore(&vaultik.RestoreOptions{
+		SnapshotID: snapshotID,
+		TargetDir:  t.TempDir(),
+	})
+	require.EqualError(t, err, "restoring "+dataPath+": downloading blob "+
+		blobHash[:16]+": "+sentence+
+		" (pass --skip-errors to continue past restore failures)")
+
+	err = v.RunDeepVerify(snapshotID, &vaultik.VerifyOptions{Deep: true})
+	require.EqualError(t, err,
+		"blob "+blobHash+" verification failed: "+sentence)
+}

internal/vaultik/snapshot_list_test.go

@@ -187,6 +187,17 @@ func (e *listEnv) addRemoteRawTimestamp(
 	t.Helper()
 
 	remoteKey := snapshot.RemoteSnapshotKey(snapshotID)
+	e.putRemoteManifest(t, remoteKey,
+		encodeRemoteManifest(t, remoteKey, timestamp))
+
+	return remoteKey
+}
+
+// encodeRemoteManifest returns the encoded manifest of a one-blob
+// snapshot whose remote key is remoteKey.
+func encodeRemoteManifest(t *testing.T, remoteKey, timestamp string) []byte {
+	t.Helper()
+
 	manifest := &snapshot.Manifest{
 		// Note: the hashed key, never the human ID. That is precisely
 		// why a remote-only snapshot cannot be named.
@@ -202,11 +213,17 @@ func (e *listEnv) addRemoteRawTimestamp(
 	data, err := snapshot.EncodeManifest(manifest, 3)
 	require.NoError(t, err)
 
-	err = e.store.Put(context.Background(),
+	return data
+}
+
+// putRemoteManifest stores an encoded manifest on the destination store
+// under remoteKey.
+func (e *listEnv) putRemoteManifest(t *testing.T, remoteKey string, data []byte) {
+	t.Helper()
+
+	err := e.store.Put(context.Background(),
 		"metadata/"+remoteKey+"/manifest.json.zst", bytes.NewReader(data))
 	require.NoError(t, err)
-
-	return remoteKey
 }
 
 // Fixtures shared across the listing tests.
@@ -791,9 +808,17 @@ func TestListSnapshots_JSONReportsTruncation(t *testing.T) {
 
 	timestamp := time.Date(2026, 3, 2, 11, 22, 33, 0, time.UTC)
 
-	// One past the cap, so exactly one snapshot is omitted.
+	// One past the cap, so exactly one snapshot is omitted. The listing
+	// names a snapshot by the key its manifest is stored under, never by
+	// the manifest's own ID. So all of them share one encoded manifest:
+	// encoding 1001 took seconds.
+	data := encodeRemoteManifest(t,
+		snapshot.RemoteSnapshotKey("otherhost_bulk"),
+		timestamp.Format(time.RFC3339))
+
 	for i := range maxRemoteOnlyRowsForTest + 1 {
-		env.addRemote(t, fmt.Sprintf("otherhost_bulk_%04d", i), timestamp)
+		env.putRemoteManifest(t, snapshot.RemoteSnapshotKey(
+			fmt.Sprintf("otherhost_bulk_%04d", i)), data)
 	}
 
 	stderr := captureProcessStderr(t, func() {

internal/vaultik/verify.go

@@ -267,6 +267,10 @@ func (v *Vaultik) downloadVerifiedSnapshotDB(
 	defer func() { _ = dbReader.Close() }()
 
 	tdb, err := v.decryptAndLoadDatabase(dbReader, identities)
+	if errors.Is(err, errWrongPrivateKey) {
+		return nil, v.deepVerifyFailure(result, opts, err.Error(), err)
+	}
+
 	if err != nil {
 		return nil, v.deepVerifyFailure(result, opts,
 			fmt.Sprintf("failed to decrypt database: %v", err),
@@ -351,9 +355,9 @@ func (v *Vaultik) decryptAndLoadDatabase(
 	reader io.ReadCloser, identities []age.Identity,
 ) (*tempDB, error) {
 	// Decrypt and decompress through the shared blobgen reader.
-	blobReader, err := blobgen.NewReader(reader, identities...)
+	blobReader, err := v.newSnapshotDBReader(reader, identities)
 	if err != nil {
-		return nil, fmt.Errorf("failed to create decryption reader: %w", err)
+		return nil, err
 	}
 
 	defer func() { _ = blobReader.Close() }()
@@ -426,7 +430,11 @@ func (v *Vaultik) verifyBlob(
 	// the plaintext as it is read. A blob's hash — its remote name — is the
 	// double SHA-256 of that plaintext (see blobgen.DoubleSHA256), not of the
 	// encrypted bytes.
-	blobReader, err := blobgen.NewReader(reader, identities...)
+	blobReader, err := v.newBlobReader(reader, identities)
+	if errors.Is(err, errWrongPrivateKeyForBlob) {
+		return err
+	}
+
 	if err != nil {
 		return fmt.Errorf("failed to create blob reader: %w", err)
 	}