Sealed

Sealed is an experimental, offline-first protocol and Rust CLI for authenticated, independent encrypted letters. It signs, encrypts, and pads a body into an opaque binary blob that can cross any byte-preserving transport. The transport is never trusted and the cryptographic core has no networking code, accounts, servers, telemetry, database, or message history.

Sealed is not a messenger, anonymity network, email system, blockchain, web application, or production-ready steganography system. It has not received an independent professional cryptographic audit. Do not rely on it for safety-critical communications yet.

Security model

V1 uses Ed25519 signatures, static and per-letter ephemeral X25519, HKDF-SHA-256, and XChaCha20-Poly1305. A recipient must pin and independently compare a contact's fingerprint. A mathematically valid signature from an unpinned identity is reported as UNKNOWN, never trusted. Outer blobs contain only an ephemeral public key, a random nonce, and authenticated ciphertext; padding is encrypted and final sizes are powers of two.

The transport may intercept, retain, modify, delete, delay, and replay blobs. V1 protects content confidentiality and authentication when endpoints and private keys remain secure. It does not hide transport-level sender/recipient metadata or timing.

Important limitations:

• Later compromise of a recipient's static X25519 key can expose recorded old blobs. V1 does not provide full forward secrecy.
• Local deletion after opening is not a cryptographic one-open guarantee. Copies can be replayed, and SSDs/filesystems may retain physical data.
• The outer format has no recognizable header, but no formal PURB or uniform-random indistinguishability claim is made.
• Linguistic steganography is an interface and research plan only; no production encoder is shipped.
• Malware, keyloggers, screenshots, cameras, compromised operating systems, physical coercion, and deliberate forwarding are out of scope.

Read the threat model, cryptographic construction, and protocol bytes before evaluating or using the software.

Use

Release bundles may include a tiny ./sealed or sealed.cmd launcher plus the appropriate prebuilt native binary under dist/. The launcher performs no download or installation. This source tree does not pretend that unbuilt cross-platform binaries are present. After a source build, simply launch the guided terminal:

./build.sh
./sealed

Running ./sealed without arguments opens an interactive menu that shows identity status and pinned contacts, then guides the user through identity creation, profile exchange, contact verification, sealing, and opening. Letters can be entered as multiple lines; a line containing only . finishes the body. Use ↑/↓ and Enter to choose menu items and contacts; j/k also work. On Unix this uses the local /bin/stty terminal utility solely for temporary key capture and falls back to numeric selection if raw terminal input is unavailable. ANSI colors are disabled when NO_COLOR is set.

The first identity wizard proposes ./.sealed-local/unlock.key automatically. This ignored directory makes a clone-and-test flow simple, but it is not the recommended storage location for real use: choose a separate removable/offline location for the unlock key instead.

The explicit commands remain available for scripts and advanced use:

# Create an identity. Choose an unlock-key path on separate media when prompted.
./sealed init

# Export the public profile without unlocking private keys.
./sealed identity export > alice.pub

# Pin Bob, then verify the displayed fingerprint out of band.
./sealed trust bob.pub

# Seal stdin to a new file. The CLI prompts for the unlock-key path.
./sealed seal bob --output letter.bin

# Open and logically delete letter.bin after successful output.
./sealed open letter.bin

# Advanced: retain the ciphertext.
./sealed open letter.bin --keep

For scripts, --unlock-key PATH or the path-only SEALED_UNLOCK_KEY environment variable avoids the terminal prompt. SEALED_HOME overrides ~/.sealed for isolated testing. Never put the unlock-key file inside the state directory.

Private plaintext is written only to stdout and kept in memory inside a best-effort zeroizing buffer. Sealing emits a blob to stdout unless --output is supplied. Keep diagnostics and trust status on stderr when redirecting data.

Build and audit

The exact Rust 1.97.1 toolchain is pinned. All crate sources are checked into vendor/; Cargo is configured offline. A source build requires Rust and a native linker, but no network access:

./build.sh

Windows PowerShell:

.\build.ps1

The underlying invariant is:

cargo build --release --offline --locked

build.sh checks formatting, compiles, tests, builds the release binary, and places it in the matching dist/<platform>/ directory. See BUILD.md and DEPENDENCIES.md. No known backdoors are intentionally present; the source is designed for independent audit, not trust in its authors or generated code.

Licensed under the MIT License.