Security and Encryption Architecture

🛡️ Security & Encryption Architecture

Secure Dialer employs a defense-in-depth security architecture designed to protect call logs, contact books, speed dials, and blocked numbers from local device malware, physical extraction, and unauthorized background inspection.

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1. Operating System-Level Network Isolation

The core pillar of Secure Dialer's zero-trust model is Hardware & OS-Level Sandboxing:

• Manifest Omission: The AndroidManifest.xml file completely omits android.permission.INTERNET and android.permission.ACCESS_NETWORK_STATE.
• Kernel Enforcement: The Android Linux kernel strictly drops any attempt to open sockets (socket(), connect()). Network calls are rejected at the system call layer.
• Zero Telemetry SDKs: The application binary contains zero analytics, tracking, or crash reporting SDKs (No Firebase, No Google Play Services, No Sentry).

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2. Hardware-Backed AES-256 GCM Database Encryption

All local app data (call history logs, contact notes, speed dial shortcuts, local encrypted contact cards, and blacklists) is stored inside a SQLCipher-encrypted SQLite database.

Key Generation & Cryptographic Lifecycle:

1. KeyStore Provider: Upon first initialization, Secure Dialer calls the Android KeyStore System (AndroidKeyStore).
2. Secure Enclave Generation: A 256-bit AES cryptographic master key is generated inside the device's hardware-isolated Trusted Execution Environment (TEE) or StrongBox Keymaster (HSM).
3. RAM Protection: The master passphrase is never stored in unencrypted persistent storage and cannot be extracted via USB debugging or root access.
4. On-Disk Cipher: SQLCipher encrypts all page sectors on disk using AES-256 in Galois/Counter Mode (GCM).

┌────────────────────────────────┐      ┌───────────────────────────────┐      ┌─────────────────────────────────┐
│     Encrypted Local Database   │ ◄──► │  SQLCipher Database Engine    │ ◄──► │  Android KeyStore System        │
│    (call_logs.db on disk)      │      │       (AES-256 GCM)           │      │   (Hardware TEE / StrongBox)    │
└────────────────────────────────┘      └───────────────────────────────┘      └─────────────────────────────────┘

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3. Isolated Encrypted Local Contacts Vault

Users can choose between two contact storage modes:

• System Contacts Integration: Standard Android ContactsContract provider integration for seamless device-wide contact management.
• Encrypted Local Contacts Vault: An isolated contacts vault stored strictly within Secure Dialer's encrypted database. Local contacts are completely invisible to other applications on your smartphone.

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4. Offline Call Screening & Zero-Latency Rejection

Unlike cloud-dependent caller ID apps that upload incoming caller numbers to remote lookup servers, Secure Dialer relies on Android's native CallScreeningService:

[ Incoming Call Event ] ──► [ CallScreeningService ] ──► [ Query SQLCipher Local DB (<5ms) ] ──► [ Reject & Silence / Allow ]
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                                                       (Zero Network Transmission)

1. Instant Local Lookup: When an incoming call arrives, CallScreeningService queries the encrypted local database in under 5 milliseconds.
2. Autonomous Decision: If the caller is on your blocklist or matches your call-blocking criteria (e.g. unknown numbers), the call is automatically rejected or silenced before your phone rings.
3. Zero Leaks: No phone numbers or timestamp telemetry leave the physical device.

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🛡️ Threat Model & Security Controls Matrix

Threat Vector	Attack Scenario	Secure Dialer Defense Control
Physical Theft / Forensic Dumping	Attacker extracts flash storage chips or takes device dump.	Database pages are encrypted with AES-256 GCM; master keys are locked in TEE / StrongBox hardware.
Malicious App Inter-Proc Extraction	Malware attempts to read local app data.	Linux UID sandboxing and file permissions prevent other apps from accessing /data/data/com.aistudio....
Network Traffic Sniffing / MITM	Attacker monitors Wi-Fi or cellular traffic for voice logs.	Internet permission is omitted; 0 bytes are transmitted over Wi-Fi or cellular networks.
Cloud Leaks & Data Subpoenas	Third-party database breaches or cloud subpoenas.	No cloud database exists. Secure Dialer developers do not host or store user data anywhere.

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