basedbank/docs/AI_SECURITY_CHECK.md

BasedBank — AI Security Audit Report

Generated by: Claude Sonnet 4.6 Date: 2026-05-16 Scope: Full source audit — credential storage, lock screen, network layer, data privacy, manifest, dependencies, backup rules. Context: This app is built from reverse-engineered protocol implementations of the official MIB (Faisanet), BML, and Fahipay Android apps. Any cryptographic weaknesses that are part of those upstream protocols are inherited constraints, not design flaws in this codebase.

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Summary

Category	Rating	Notes
Credential storage at rest	Excellent	AES-256-GCM, Android Keystore
Lock screen hashing	Excellent	PBKDF2-HMAC-SHA256, 100k iterations
Screen capture protection	Good	FLAG_SECURE on by default
Backup exclusion	Excellent	All sensitive prefs excluded
Manifest attack surface	Excellent	Only MainActivity exported
Third-party data leakage	None	Zero analytics/tracking SDKs
Certificate pinning	Missing	Biggest actionable gap
Brute-force resistance	Weak	5 attempts / 30s — too short
Lockout bypass (rooted device)	Possible	Counter stored in plain prefs
MIB transport crypto	Upstream constraint	Blowfish/ECB is the MIB protocol
Code obfuscation	N/A	Open-source app, not applicable

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1. Credential Storage

File: app/src/main/java/sh/sar/basedbank/util/CredentialStore.kt

All credentials, session tokens, OTP seeds, and PII are encrypted before being written to SharedPreferences using AES-256-GCM with a key generated and stored inside the Android Keystore (hardware-backed on supported devices). The key never leaves the secure enclave.

Encrypted data:

• MIB username, password hash, OTP seed, session keys (key1/key2), app ID
• BML username, password, OTP seed, access token, device ID
• Fahipay ID card, password, authId, session cookie (__Secure-sess), device UUID
• PIN/pattern PBKDF2 hash + salt
• All user profile PII (full name, email, mobile, NID, customer ID)

The IV is randomly generated per encryption call and stored alongside the ciphertext (iv:ciphertext Base64 format), so each encrypted value is unique even with the same plaintext.

Cache encryption (CacheEncryption.kt) reuses the same AndroidKeyStore key for all cache SharedPreferences — consistent and correct.

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2. Lock Screen

File: app/src/main/java/sh/sar/basedbank/LockActivity.kt File: app/src/main/java/sh/sar/basedbank/ui/onboarding/SecuritySetupFragment.kt

PIN / Pattern Hashing

• Algorithm: PBKDF2WithHmacSHA256
• Iterations: 100,000
• Salt: 16 bytes, SecureRandom-generated, unique per setup
• Output: 256-bit key stored encrypted in CredentialStore (AndroidKeyStore)
• Password array is cleared via PBEKeySpec.clearPassword() after use

Legacy Migration

Old installs used raw SHA-256(salt + input) stored in plaintext SharedPreferences. On the first successful unlock, the app transparently migrates to PBKDF2 + CredentialStore and removes the legacy plaintext fields.

Biometrics

• Uses androidx.biometric with BIOMETRIC_WEAK authenticators
• Falls back to PIN/pattern if biometrics unavailable or cancelled

Brute-Force Lockout

• Max attempts: 5
• Lockout duration: 30 seconds
• Attempt counter stored in lock_attempts SharedPreferences

Weakness: The lockout is weaker than ideal for two reasons:

1. 30 seconds is very short — an attacker gets ~10 guesses/minute, ~600/hour.
2. The lock_attempts.xml SharedPreferences file is not encrypted. On a rooted device, deleting this file resets the counter entirely, bypassing brute-force protection.

A stronger policy would use progressive delays (1 min, 5 min, 15 min, 1 hour) and store the counter inside CredentialStore.

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3. Autolock

File: app/src/main/java/sh/sar/basedbank/ui/home/HomeActivity.kt

• Autolock timer resets on every user interaction (onUserInteraction)
• Warns the user 10 seconds before locking with a countdown dialog
• On resume, checks elapsed pause time and locks immediately if the timeout was exceeded while the app was backgrounded
• Default timeout: 60 seconds (configurable in Settings)

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4. Screen Capture Protection

File: app/src/main/java/sh/sar/basedbank/ui/home/HomeActivity.kt:80

FLAG_SECURE is applied on HomeActivity creation, blocking screenshots and hiding app content in the recents/app-switcher. This is enabled by default and can be toggled off by the user in Settings.

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5. Network Layer

Endpoints

All network traffic goes exclusively to the banking backends:

Backend	Host
MIB (Faisanet)	https://faisanet.mib.com.mv
MIB WebView/KeepAlive	https://faisamobilex-wv.mib.com.mv
BML	https://www.bankofmaldives.com.mv
Fahipay	https://fahipay.mv

No analytics endpoints, no crash reporters, no CDN telemetry. Zero external data sharing.

MIB Transport Cryptography (Upstream Protocol Constraint)

File: app/src/main/java/sh/sar/basedbank/api/mib/MibCrypto.kt

The MIB Faisanet API uses Blowfish/ECB/PKCS5Padding for payload encryption. ECB mode does not use an IV, meaning identical plaintext blocks produce identical ciphertext blocks, and block patterns can be analysed. This is the protocol defined by MIB's own servers and official app — it is an upstream constraint inherited from the reverse-engineered protocol, not a choice made in this codebase.

The session key itself is derived via a Diffie-Hellman exchange (2048-bit+ modulus) with SHA-256 key derivation, which provides forward secrecy per session. The hardcoded DEFAULT_KEY is only used as the bootstrap key for the initial DH handshake; all subsequent requests use the DH-derived session key.

Certificate Pinning

File: app/src/main/res/xml/network_security_config.xml

The network security config is empty (<network-security-config/>), meaning the app relies on Android's default system CA trust store. There is no certificate pinning for any of the three banking backends.

Risk: A device with a malicious or corporate CA certificate installed (e.g. MDM, proxy, or a compromised CA) could perform a man-in-the-middle attack against all API traffic. This is the most significant actionable security gap in the app.

Recommendation: Add <pin-set> entries for each banking domain's leaf or intermediate certificate in network_security_config.xml.

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6. Third-Party Data Leakage

No user data is sent to any third party or the developer.

Dependency Audit

Library	Purpose	Phones Home?
androidx.*	UI / Lifecycle / Navigation	No
com.google.android.material	Material Design UI components	No
com.squareup.okhttp3:okhttp	HTTP client	No
androidx.camera.*	QR scanner camera	No
com.github.markusfisch:zxing-cpp	QR barcode decoding	No
androidx.biometric	Biometric authentication	No
org.jetbrains.kotlinx:kotlinx-coroutines-android	Coroutines	No

No Firebase, no Crashlytics, no analytics SDKs, no ad networks.

Logging

There are zero android.util.Log calls anywhere in the codebase. Nothing is written to logcat. The okhttp3:logging-interceptor dependency has been removed.

TOTP

Totp.kt is a self-contained RFC 6238 implementation using only javax.crypto from the Android standard library. No third-party OTP SDK is used.

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7. Backup & Data Extraction

Files: app/src/main/res/xml/backup_rules.xml, app/src/main/res/xml/data_extraction_rules.xml

All sensitive SharedPreferences files are excluded from both Android cloud backup (API 31+) and device-to-device transfer:

• credential_store.xml
• mib_prefs.xml
• prefs.xml
• account_cache.xml
• contacts_cache.xml
• financing_cache.xml
• foreign_limits_cache.xml
• recents_cache.xml
• lock_attempts.xml
• cache/ directory

Note: even if backup were to occur, the AndroidKeyStore encryption key is hardware-bound and does not leave the device, so the encrypted data would be unreadable without the original device's secure hardware.

The manifest has android:allowBackup="true", but the exclusion rules above make the effective backup content empty of anything sensitive.

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8. Manifest & Attack Surface

File: app/src/main/AndroidManifest.xml

Only MainActivity is android:exported="true" (required as the launcher entry point). All other activities (LockActivity, OnboardingActivity, LoginActivity, HomeActivity, QrScannerActivity) are exported="false" and cannot be launched by external apps.

The FileProvider is exported but with android:grantUriPermissions="true" scoped correctly — it cannot be accessed without an explicit URI grant.

Permissions

Permission	Reason
INTERNET	Banking API calls
CAMERA	QR scanner
USE_BIOMETRIC	Biometric unlock
ACCESS_NETWORK_STATE	Network availability checks
WRITE_EXTERNAL_STORAGE	Receipt saving, limited to API ≤ 28

No READ_CONTACTS, no READ_SMS, no RECEIVE_SMS, no location permissions.

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9. Code Obfuscation

isMinifyEnabled = false in the release build config. This is not a security concern because BasedBank is an open-source project — the source code is already publicly available. Obfuscating the APK would provide no additional protection when the source is readable. The only benefit of enabling R8 would be APK size reduction via dead-code elimination.

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Findings Summary

Critical

None.

High

• No certificate pinning — MITM possible on devices with untrusted CA certs installed.

Medium

• Weak lockout policy — 30-second lockout after 5 attempts; no progressive backoff.
• Lockout counter not encrypted — lock_attempts.xml is plaintext; deletable on rooted devices.

Low / Informational

• BIOMETRIC_WEAK allows 2D face unlock on some devices, which may be spoofable with a photo.
• MIB Blowfish/ECB — inherited upstream protocol weakness, not actionable without server-side changes.
• android:allowBackup="true" — flagged by automated scanners but effectively mitigated by the exclusion rules.