[SEC-05] Web/PWA: Stellar secret key stored in plaintext localStorage

[grantfox-oss]

Problem

Web/PWA build stores the full Stellar secret key (S...) in plaintext localStorage under key stellar_keypair.

Root Cause

micopay/frontend/src/services/secureStorage.ts selects storage backend at runtime:

• Native (Capacitor): @aparajita/capacitor-secure-storage → Android Keystore (encrypted)
• Web/PWA: custom webStore wrapper → window.localStorage.setItem('stellar_keypair', JSON.stringify({ publicKey, secretKey })) PLAINTEXT

Impact

Vector	Risk
XSS	Any XSS in the SPA → localStorage.stellar_keypair → full wallet control
Malicious extension	Browser extensions with host permissions read all localStorage
DevTools / debugging	Secret visible in Application tab, crash reports, HAR files
Shared device	Anyone with browser access extracts the seed

Severity: HIGH — Single XSS = total account compromise (all funds).

Evidence

// micopay/frontend/src/services/secureStorage.ts:13-23
const webStore: KvStore = {
  async get(key: string) {
    const v = localStorage.getItem(key);
    return v ? JSON.parse(v) : null;
  },
  async set(key: string, value: unknown) {
    localStorage.setItem(key, JSON.stringify(value)); // ← secretKey stored in plaintext
  },
  // ...
};

// micopay/frontend/src/services/secureStorage.ts:27-30
async function getStore(): Promise<KvStore> {
  if (!Capacitor.isNativePlatform()) return webStore; // ← Web/PWA gets plaintext store
  // ...
}

Solution Options

Option	Approach	Effort	Security
A	WebCrypto SubtleCrypto.encrypt() with key derived from user passphrase (PBKDF2)	Medium	🟢 Encrypted at rest
B	WebCrypto generateKey({ extractable: false }) — non-extractable key in CryptoKey object, only usable via sign()/unwrapKey()	Medium	🟢 Key never leaves browser crypto subsystem
C	indexedDB + CryptoKey storage (same as B, persistent)	Medium	🟢 Persistent, non-extractable
D	Deprecate web secret storage — require native app for custodial features	Low	🟢 Eliminates web risk

Recommended: Option B — Non-extractable CryptoKey for signing operations, secret never in JS memory as string.

Acceptance Criteria

• secretKey never written to localStorage / indexedDB / any persistent storage in plaintext
• Web build uses SubtleCrypto non-extractable key for all signing operations
• Secret export (backup) only via user-initiated flow: QR code / encrypted file / password manager — never clipboard
• Migration: existing localStorage.stellar_keypair detected → re-encrypted or purged on next load
• Tests: XSS simulation cannot extract usable secret

Files to Modify

• micopay/frontend/src/services/secureStorage.ts (new webCryptoStore)
• micopay/frontend/src/lib/keystore.ts (use crypto store for signing)
• micopay/frontend/src/pages/Profile.tsx (remove clipboard export, add secure backup)
• New test: micopay/frontend/src/services/secureStorage.test.ts

References

• SEC-05 security report (full analysis)
• SEC-22 localstorage secure storage (related)
• SEC-25 secret key clipboard (related — web clipboard also affected)

Labels

security, complexity: high, GrantFox OSS, frontend, web, pwa, crypto, stellar

[waterWang]

I claim this bounty. I will implement WebCrypto non-extractable key encryption (Option B) for the web/PWA localStorage secret key storage, following the detailed acceptance criteria in the issue description.