8e26c8708b
Clarifies what AEAD protects (tampering) vs. what it doesn't (deletion, rollback). Documents that git history is the audit trail and device authentication is the mitigation. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
62 lines
2.0 KiB
Markdown
62 lines
2.0 KiB
Markdown
# Relicario Security Model
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## Cryptographic Protection
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Relicario uses two-factor vault decryption:
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1. **Passphrase** — user-memorized, zxcvbn score ≥3 required
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2. **Reference image** — JPEG carrying 256-bit secret via DCT steganography
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Key derivation: Argon2id (64 MiB memory, 3 iterations, 4 parallelism)
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Encryption: XChaCha20-Poly1305 (192-bit nonce, 256-bit key)
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## Manifest Integrity
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The manifest (`manifest.enc`) is encrypted with AEAD, which provides:
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- **Confidentiality**: Contents unreadable without master key
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- **Integrity**: Any modification detected and rejected on decrypt
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- **Authenticity**: Only master key holders can create valid ciphertexts
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### What AEAD Does NOT Protect
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- **Item deletion**: An attacker with write access can delete `.enc` files
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or git-revert commits. The manifest decrypts successfully but won't
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contain the deleted items.
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- **Rollback attacks**: An attacker can replace `manifest.enc` with an
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older valid version. AEAD accepts any ciphertext created with the key.
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### Mitigation
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Item deletion and rollback are detectable via **git history**:
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```bash
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git log --oneline items/
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```
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For environments where git history could be rewritten (force-push):
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1. Enable device authentication (commit signing + pre-receive hook)
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2. Use a git server that rejects non-fast-forward pushes
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3. Regular backups with `relicario backup export`
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## Device Authentication
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When enabled, device authentication provides:
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- **Commit authorship**: All commits signed by registered device keys
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- **Push access control**: Deploy keys managed via Gitea API
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- **Instant revocation**: One command cuts off both signing and push
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See `docs/superpowers/specs/2026-05-02-device-authentication-design.md`.
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## Access Control
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Without device authentication, access control is transport-layer only:
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- **CLI**: SSH key authentication to git remote
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- **Extension**: Git credentials in browser storage
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Device registration was optional before v0.4.0. With device auth enabled,
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all commits must be signed by a registered device.
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