SHIELD: SIGNED BACKUP

LYTA Shield protects against:

1. Output containing commands that would compromise the host if copied/pasted into a terminal.
2. Adversarial prompts instructing the model to emit dangerous commands.
3. Browser-side prompt injection or credential exfiltration.
4. Local tampering with the LYTA Shield codebase or configuration.

• 0 — SAFE
• 1 — SUSPICIOUS (confirm with user)
• 2 — DANGEROUS (block, never execute)

Every critical file in the repository is protected by a signed backup chain:

1. scripts/backup-sign.py creates a tarball of the repository tree, computes SHA-256, and signs the backup with Ed25519.
2. scripts/verify-backup.py reconstructs the signed message and verifies it against the external trust anchor. A manifest can never select its own verification key.
3. bin/lyta-shield backup creates a new signed backup; bin/lyta-shield verify-backup checks the latest.
4. Self-heal accepts repository Git-object bytes or a verified backup member only when the bytes match the pinned per-file integrity digest. It never downloads mutable branch content or calls extractall().

• var/keys/backup-sign.nacl — Ed25519 private key (keep secret, never commit).
• var/keys/backup-sign.nacl.pub — local Ed25519 public key.
• ~/.config/lyta-shield/trusted-backup.pub — external verification trust anchor. Override with LYTA_BACKUP_PUBLIC_KEY when isolation requires another path.

The private key must be one regular file with exact mode 0600; symlinks and partial keypairs are rejected. Explicit rotation with scripts/rotate-backup-key.py updates the keypair and trust anchor. Create a fresh backup immediately afterward because backups signed by the retired key no longer verify against the new anchor.

• bin/lyta-shield restore-baseline atomically creates a repository-relative SHA-256 baseline for the protected file set.
• bin/lyta-shield doctor checks the baseline, backup status, and circuit breaker.
• bin/lyta-shield self-heal atomically restores exact baseline bytes and preserves the trusted file mode.
• bin/lyta-shield incident logs security events to var/incidents/.

• Daily backup: lyta-shield-daily-backup at 06:30.
• Weekly verification: lyta-shield-weekly-verify on Sundays at 07:00.
• Daily self-audit: lyta-shield-daily-self-audit at 06:00.
• Doctor/heal: lyta-shield-doctor-heal every 10 minutes.

See self-audit-log.md for historical incidents and self-audit results.