repository: reject key and config files that are too short (#21977)

Signed-off-by: Arpit Jain <arpitjain099@gmail.com>

internal/repository/key.go

@@ -98,6 +98,10 @@ func openKey(ctx context.Context, s *Repository, id restic.ID, password string)
 	}
 
 	// decrypt master keys
+	if len(k.Data) < crypto.CiphertextLength(0) {
+		return nil, errors.New("invalid key file, data too short")
+	}
+
 	nonce, ciphertext := k.Data[:k.user.NonceSize()], k.Data[k.user.NonceSize():]
 	buf, err := k.user.Open(nil, nonce, ciphertext, nil)
 	if err != nil {