masvs-crypto-review

name	masvs-crypto-review
description	Deep audit of cryptographic implementations against OWASP MASVS-CRYPTO controls. Use when code generates keys, encrypts/decrypts data, uses hashing, or touches AndroidKeyStore / iOS Keychain.

Cryptography Review (MASVS-CRYPTO)

Context: See .ai-context/security-instructions.md for when to invoke this skill and the full MASVS coverage map for Dividox.

Controls Assessed

Control	Requirement
MASVS-CRYPTO-1	App uses current, industry-standard cryptography
MASVS-CRYPTO-2	Cryptographic keys managed securely throughout their lifecycle

Algorithm Classification

❌ Deprecated — FAIL immediately

Algorithm	Issue
DES, 3DES	Broken
RC4	Broken
MD5, SHA-1 (security use)	Collision-prone
RSA < 2048-bit	Insufficient key length
java.util.Random	Not cryptographically secure
ECB mode (any cipher)	Deterministic, pattern-leaking

✅ Acceptable

Algorithm	Notes
AES-256-GCM	Preferred for symmetric encryption
AES-256-CBC + HMAC-SHA256	Acceptable with random IV
ChaCha20-Poly1305	Good for KMP/mobile
RSA ≥ 2048-bit with OAEP	For key wrapping
SHA-256 / SHA-512	General hashing
Argon2id / bcrypt / scrypt	Password hashing
SecureRandom	Required for all random bytes

Audit Scope for Dividox

Dividox uses cryptography for:

• OAuth token storage (Android Keystore / iOS Keychain)
• Encrypted local preferences (EncryptedSharedPreferences)
• Any future biometric-bound key operations

Android (androidMain)

• KeyGenParameterSpec must specify purpose (ENCRYPT|DECRYPT or SIGN|VERIFY).
• Block mode must not be ECB.
• Key must be bound to user authentication if protecting financial data.
• setRandomizedEncryptionRequired(true) must be set (enforces random IV).

iOS (iosMain)

• Keys stored in Keychain with kSecAttrAccessibleWhenUnlockedThisDeviceOnly.
• CryptoKit preferred over legacy CommonCrypto.
• SecKey operations must use OAEP for RSA.

KMP Common (commonMain)

• kotlinx-crypto or platform-specific expects must use algorithms from the acceptable list.
• No hardcoded IV, salt, or key material anywhere in source.

Audit Steps

1. Inventory all crypto operations — search: Cipher, KeyGenerator, MessageDigest, SecretKey, CryptoKit, SecKey, AES, RSA, SHA.
2. Check algorithm choice against approved list above.
3. Verify key generation uses KeyGenParameterSpec (Android) or SecKeyGenerateSymmetric (iOS).
4. Scan for hardcoded secrets — base64 blobs, hex strings, "key", "secret", "iv" literals.
5. Verify IVs are random — never reused or derived from predictable input.
6. Confirm key storage in Keystore/Keychain (not in SharedPreferences or files).

Output Format

## MASVS-CRYPTO Audit Report

### Cryptographic Inventory
| Location | Algorithm | Mode | Key size | Storage | Status |
|----------|-----------|------|----------|---------|--------|

### CRYPTO-1 — Standard Algorithms
- [FAIL/WARN/PASS] {finding} — {file}:{line}

### CRYPTO-2 — Key Management
- [FAIL/WARN/PASS] {finding} — {file}:{line}

### Summary
- FAIL: {n} | WARN: {n} | PASS: {n}
- Verdict: APPROVED / BLOCKED

MASTG Test Mappings

• MASTG-TEST-0013: Testing the Configuration of Cryptographic Standard Algorithms (Android)
• MASTG-TEST-0014: Testing Random Number Generation (Android)
• MASTG-TEST-0060: Testing the Configuration of Cryptographic Standard Algorithms (iOS)