Seca

Three communication apps for Android: Seca Contacts, Seca Phone and Seca Messages. One Material 3 Expressive design, privacy first, no Google dependency. They run on any phone with Android 12 or newer, and are at their best on GrapheneOS. The apps speak English and French, following the phone's language.

Seca Contacts	Seca Phone	Seca Messages

The apps

Seca Contacts: the address book, in Android's own contacts. Colored profiles (Family, Work…) shared with the other two apps, favorites, search, duplicate merging, your own card shared by QR code, vCard import and export that keeps each contact's profile, encrypted backup. No Internet permission.

Seca Phone: calls. A call screen showing the caller's profile, T9 search, telemarketing blocking (the number ranges reserved for it in France), unknown callers silenced, profiles blocked for a chosen time, a remembered SIM for each contact, declining a call with a message, named audio and Bluetooth outputs. No Internet permission.

Seca Messages: texts, and Seca Link. Conversations in the colors of the contact's profile, scheduled messages, verification codes erased after a delay, advertising texts filed away, encrypted backup. And, between Seca phones, Seca Link.

From any of the three, a suite backup gathers contacts and profiles, call history and filtering, texts, conversations and settings into a single encrypted file, to move to a new phone.

Seca Link

End-to-end encrypted messaging between Seca phones, with no account and no Seca server.

• The encryption is Signal's: libsignal, with the post-quantum PQXDH key agreement.
• Encrypted messages travel through public Nostr relays. Each envelope is signed by a throwaway key: a relay sees who receives, when and roughly how much, never who writes nor what is written.
• Two phones that both have Seca Link connect on their own: a data SMS a phone without Seca never shows, sent when a conversation opens or a message is exchanged. The conversation then says so, and turns encrypted. Scanning each other's code in person works too.
• Read receipts, typing indicator, reactions, quoted replies, encrypted photos and voice messages, disappearing messages, a safety number to compare.
• A contact who turns Seca Link off tells your phone at once: the conversation says so, the lock goes, and what you write leaves as an ordinary SMS. One who takes Seca off their phone says nothing — nothing runs there any more — so their keys stop being refreshed and expire within a day, which ends the conversation the same way.
• A contact's new phone brings a new key. Only your side, the one that did not change phone, is told, and the safety number is there to compare.
• A Tor option with Orbot: relays no longer see the phone's address.
• Off by default. Without Seca Link, Seca Messages does not use the Internet.

Privacy

• No analytics, no crash reporting, no trackers.
• Seca Contacts and Seca Phone do not have the INTERNET permission: they cannot send anything anywhere.
• Each app checks at build time that no com.google.android.gms, com.google.firebase or com.google.android.play artifact reaches its runtime: the verifyReleaseNoProprietaryDependencies task, wired into check, fails the build otherwise.
• Seca Contacts' profiles can only be read by apps signed with the same key.

What Seca does not do

• No RCS. Google keeps its RCS API to a closed list of apps.
• No Wi-Fi calling as such. VoWiFi belongs to the system's IMS stack and works whatever the dialer; Seca Phone shows its state.

Which phone?

Any phone with Android 12 or newer: Samsung, Xiaomi, OnePlus, Fairphone, Pixel… Seca needs neither Google Play nor Google services, and uses neither when they are there.

GrapheneOS is recommended, not required. Seca keeps what it handles on the phone whatever the system, but only a system without Google keeps the rest of the phone as discreet. GrapheneOS also brings features Seca makes use of: Contact Scopes, a network permission for each app, and a hardened system.

On other phones:

• Seca Link receives through its own connection to the relays, not through Google's push service. Let Seca Messages run in the background when it asks. Some brands (Xiaomi, Huawei, Oppo, Samsung…) add their own battery or autostart settings on top: dontkillmyapp.com explains them brand by brand.

Install

Seca is in beta. Until it reaches F-Droid (the state of that is in docs/fdroid.md), releases are published on GitHub Releases: install the three APKs, then choose Seca Phone as the Phone app and Seca Messages as the SMS app.

The APKs are signed with this certificate (SHA-256 fingerprint):

2F:DE:A7:B4:6B:EF:FE:16:45:9B:B4:DC:DD:34:DB:5E:0C:B9:12:27:4A:5E:B6:28:E4:B0:D8:A5:96:21:17:90

Build

Requirements: JDK 17 and the Android SDK (platform android-37, build-tools 36.0.0). The Seca Link tests also need a JDK 25, which Gradle finds by itself.

./gradlew :apps:contacts:assembleDebug :apps:phone:assembleDebug :apps:messages:assembleDebug
./gradlew test
./gradlew check

To draw the main screens with sample data (the screenshots of this README and of the F-Droid listings):

SECA_SCREENSHOTS=build/captures ./gradlew testDebugUnitTest --tests "*ScreenshotsTest"

License

GPL-3.0-or-later.