MessageSeal

New: Nearby Exchange for local device-to-device key setup, safety-code checks, and stronger backups.

MessageSeal lets you encrypt text or sign readable messages on your device, then share the result through the apps you already use.

Create one or more local identities. Each identity bundles separate encryption and signature keys under one label. Share your signed public identity bundle, import other people's identities, and keep private keys on device. Write a message, choose Encrypt to create a MessageSeal1 bundle for saved recipients, or choose Sign to keep the text readable and add a detached signature footer that recipients can verify later. If you include a sender identity while encrypting, the encrypted bundle can also carry sender authentication. The app also includes a Messages extension so you can encrypt, sign, share your identity, and open compatible protected text inside Messages on device.

If the other person is nearby, Nearby Exchange can swap signed public identities, compare the same safety code on both screens, and save the other person's public identity for later use. Nearby Exchange is main-app-only, foreground-only, and does not add a backend, inbox, or chat history.

What makes it different:

• Nearby Exchange for device-to-device identity setup and safety-code comparison
• One pinned Apple-native crypto profile at a time instead of in-band suite negotiation
• Apple-native XWing HPKE recipient wrapping plus AES-256-GCM for encrypted text
• Apple-native hybrid ML-DSA87 + P521 signatures with SHA-512 for readable signed messages
• Authenticated encrypted messages and signed plaintext in one app
• On-device key generation, encryption, signing, decryption, and verification
• One signed shareable public identity bundle with separate encryption and signature keys
• Saved nearby recipients remain usable later even after the nearby session ends
• 128-bit verification fingerprints for serious out-of-band checks
• Private keys stored as device-only Keychain items for the app and its Messages extension
• Optional app lock and optional Messages extension lock with device authentication
• Encrypted identity backup with password strength guidance and restore verification
• No account, no server, no analytics, and no cloud sync
• Support for multiple local identities and multiple saved recipients
• Guided tour, Protocol Specification, glossary, and in-app help that explain the workflow clearly

MessageSeal is a lockbox, not a mailbox. It protects message contents before you send them through another app, and Nearby Exchange only helps with local identity setup. It does not run a chat network or message relay service.

Why post-quantum matters:

Traditional public-key systems are expected to become weaker if future large-scale quantum computers become practical. MessageSeal keeps the same local-only workflow as the earlier release, but the current version moves the public-key layer to Apple-native hybrid post-quantum cryptography for recipient encryption and signatures so long-lived sensitive text is not tied only to older public-key designs. The app pins one crypto profile at a time to avoid downgrade-prone negotiation, and the current profile keeps a classical hedge during the transition instead of relying on only one newer post-quantum primitive. The app uses AES-256-GCM for the message body because strong symmetric cryptography remains appropriate here.

Important:

Encrypted bundles protect message contents, and authenticated encrypted bundles can also prove continuity of the included sender signing key. Signed plaintext proves continuity of the included signing key and identity data, but it does not prove transport metadata or a human name by itself. Verify public identities through a trusted out-of-band channel before you rely on them. Nearby Exchange safety codes prove that both nearby devices saw the same exchanged identity continuity data, but they still do not prove a claimed human name by themselves.