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Defense in Depth

Six Layers.
No Single Weak Point.

Each layer was chosen to defeat a different attack.
Compromise one. The rest still hold.
citadelvault.org

The Stack: Bottom to Top

Get past the hardware and there's the OS. Past the OS, the application. Past the application, the cryptography. Each layer is designed to exhaust a different kind of threat. Defeat the encryption and the air gap still holds. Defeat the hardware and the ceremony still blocks access. There is no single path through.

6
Recovery Protocol
Open CAF spec · Bitcoin time-proof · M-Disc archival · no vendor lock-in
5
Threshold Ceremony
k-of-n Shamir on NFC smartcards · single-owner session · memory zeroed on close
4
Cryptographic Stack
Argon2id → HKDF-SHA256 → AES-256-GCM: three algorithms, three different threats
3
Audited Application
Rust · reproducible builds · symbol audit · zero network code linked in the binary
2
Hardened OS
Minimal Debian · no network stack · no Bluetooth · no SSH · read-only root
1
Air-Gapped Hardware
No network chips · no Bluetooth · no camera · signed model manifest verified at boot
Layer 1

Air-Gapped Hardware

Physical isolation is the precondition for everything above it. A compromised OS can't steal what it can't touch. No reach, no attack.

  • No network chips soldered to the board: not disabled in software, physically absent
  • No WiFi, no Bluetooth, no LTE, no Ethernet controller
  • No camera, no microphone: no optical or acoustic side-channel
  • USB-A ports only: for the Vault Drive and keyboard. No wireless adapter can load without a driver that doesn't exist on the OS.
  • Signed model manifest checked at boot: tampering with the hardware is detectable before the OS loads

Air gap is not a setting. It is physics.

6
Recovery Protocol
5
Threshold Ceremony
4
Cryptographic Stack
3
Audited Application
2
Hardened OS
1
Air-Gapped Hardware
What this defeats
Remote code execution Wireless exfiltration Network-side supply chain attacks Acoustic side-channels
Layer 2

Hardened OS

Air-gapped hardware is necessary, not sufficient. A bloated OS carries services, daemons, and places an attacker could write to or corrupt. Hardening means removing everything that isn't Vault OS — no browser, no mail client, nothing else to compromise.

  • Read-only root filesystem: nothing written to disk at runtime. Malware has no persistence vector.
  • No SSH daemon, no cron, no print spooler, no Avahi, no cups. Nothing listening on any socket.
  • No Bluetooth stack compiled in: not just disabled, not present in the image
  • No network interfaces configured: the kernel has no IP stack to route through
  • Minimal Debian base: only packages required to run Vault OS. Fewer packages means fewer places to hide.
  • Overlayfs for transient state: anything written during a session disappears on reboot

A service that doesn't run can't be exploited. A filesystem that can't be written to can't be infected.

6
Recovery Protocol
5
Threshold Ceremony
4
Cryptographic Stack
3
Audited Application
2
Hardened OS
1
Air-Gapped Hardware
What this defeats
Persistent malware Privilege escalation via daemons Local socket attacks Bluetooth stack exploits
Layer 3

Audited Application

Before the application touches cryptographic material, three decisions have to be right: what language it's written in, whether the binary can be independently verified, and whether network calls are structurally impossible. Get any one wrong and you've left a gap in the perimeter.

  • Rust throughout: the borrow checker eliminates buffer overflows, use-after-free, and null pointer dereferences at compile time. Entire categories of exploit simply cannot exist.
  • Reproducible builds: any third party can compile from source and verify the shipped binary matches exactly. Nothing hidden in the distribution pipeline.
  • Symbol audit: the compiled binary contains zero dynamic symbols from networking libraries. It doesn't refuse to connect. It has no code path that leads there.
  • Dependency supply chain: all Rust crates are pinned and audited. No surprise transitive dependency pulling in a network stack.

Network calls aren't blocked at runtime. They can't be compiled in. The program was never written to make that call — there's no call to intercept.

6
Recovery Protocol
5
Threshold Ceremony
4
Cryptographic Stack
3
Audited Application
2
Hardened OS
1
Air-Gapped Hardware
What this defeats
Memory corruption exploits Tampered binary distribution Hidden network calls Malicious transitive dependencies
Layer 4

Cryptographic Stack

Input

Vault Master
Passphrase

→
Step 1: KDF

Argon2id

Memory-hard: each guess requires a full pass through RAM, with no shortcuts and no way to parallelize the work.

→
Step 2: Key Split

HKDF-SHA256

Derives two independent subkeys. Compromising one reveals nothing about the other.

→
Step 3: Seal

AES-256-GCM

Encrypts and authenticates. Any modification (even one bit) is detected on read.

→
Output

Encrypted
Vault Block

65 MB RAM per guess. GPU clusters can't parallelize it. An attacker running full clusters would still be guessing long after the hardware running it is a museum piece.

Two keys derived independently. A flaw in one key's usage tells an attacker nothing about the other.

Encryption is the lock. Authentication is the seal. A lock keeps people out — a seal tells you someone was already in. One tampered bit and the vault won't open.

What this defeats: Password brute force GPU dictionary attacks Key reuse cascade Silent ciphertext tampering
Layer 5

Threshold Ceremony

Holding the Vault Drive gets you nothing. Think of a safe-deposit box that requires two keys held by two different people — neither one can open it alone. The vault works the same way. The drive is encrypted with a passphrase split across Vault Cards. A "ceremony" here means a required gathering: the right people, the right cards, the same room. Without that quorum, the vault cannot be opened.

  • Shamir's Secret Sharing: the passphrase is mathematically split across Vault Cards. Below the threshold, a card doesn't just resist attack — it reveals nothing. Mathematically nothing. Not "hard to extract." Zero.
  • Standard 2-of-3 setup; 3-of-5 available. Six cards ship per kit: two per shard position, so a lost card has a backup.
  • EAL6+ secure elements: same evaluation level as biometric passports and banking chips. Cards self-wipe after repeated failed PIN attempts.
  • Single-owner session: Vault OS runs one reconstruction ceremony at a time, with no concurrent sessions possible.
  • Memory zeroed on session close: the reconstructed passphrase is actively overwritten before the session ends. No window for a cold-boot read.

Your heir must bring the right people together, in person. A vault that one person can open alone is a vault that one person can be forced to open — under pressure, or in grief.

6
Recovery Protocol
5
Threshold Ceremony
4
Cryptographic Stack
3
Audited Application
2
Hardened OS
1
Air-Gapped Hardware
Spouse
Card 1
Attorney
Card 2
Adult Child
Card 3
What this defeats
Single-point compromise Physical coercion of one holder Cold-boot RAM attacks Brute-force card PIN
Layer 6

Recovery Protocol

The top layer isn't about cryptography. It protects against vendor shutdown, media failure, and any attempt to force the vault open before its time — whether through a court order or physical coercion. A vault that stops working when we do isn't really yours.

You're not trusting us to stay in business. You're trusting math that has been public for decades.

  • Open CAF format: published specification. Any developer can write a compatible reader independently. The vault does not depend on CitadelVault remaining in business.
  • Bitcoin block-height timelock: the heir presents block headers from a microSD. The chain verifies elapsed time. No vendor, no notary, no server enforces the waiting period. Bitcoin's proof of work is the clock.
  • M-Disc archival: 1,000-year rated optical media. Outlasts USB drives, consumer SSDs, and magnetic storage in a drawer.
  • 3-3-3 backup standard: three copies across three media types, all air-gapped. Losing any single item leaves recovery intact.
  • Every cryptographic primitive is public domain, independently implemented in dozens of open-source libraries. Decades of public scrutiny. Nothing has broken. Nothing proprietary.
6
Recovery Protocol
5
Threshold Ceremony
4
Cryptographic Stack
3
Audited Application
2
Hardened OS
1
Air-Gapped Hardware
What this defeats
Vendor lock-in Media failure Premature forced access Company failure Single copy loss
Early Bird: 21 Units Only
$2,395
Regular price $2,995
Pre-sale opens May 12

No subscription, no telemetry, no cloud dependency — just math that doesn't expire.

citadelvault.org

Six layers. One design principle.

  • Layer 1: no network chips. No remote access. The attack surface is gone before the OS boots.
  • Layer 2: read-only root. Malware that lands doesn't survive a reboot.
  • Layer 3: Rust eliminates memory corruption at compile time. Zero network symbols in the binary.
  • Layer 4: 65 MB RAM per guess. Two independent keys. Every byte authenticated.
  • Layer 5: below the threshold, a card reveals nothing. Not hard to crack — mathematically impossible.
  • Layer 6: open spec. M-Disc outlasts any USB drive. The timelock runs on Bitcoin, not on us.

Your instructions are sealed inside. When you're gone, your family will know exactly what to do.