cyb/docs/security_audit_private_key_import.md

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Security Audit: Private Key Import Feature

Date: 2026-05-12 Status: PASSED — 0 critical, 0 high, 0 medium, 1 low (optional) Scope: Addition of raw secp256k1 private key import to wallet

Changes Audited

File Change
src/types/defaultAccount.d.ts Added 'private-key' to keys union type
src/utils/offlineSigner.ts CybPrivateKeySigner class + getOfflineSignerFromPrivateKey()
src/pages/Keys/ActionBar/ConnectWalletModal/ConnectWalletModal.tsx UI tabs, private key input field
src/pages/Keys/ActionBar/actionBarConnect.tsx Import routing, encryption, account registration
src/contexts/signerClient.tsx Unlock and auto-switch for private-key accounts
src/redux/features/pocket.ts Deletion cleanup for private-key accounts

Threat Model

Threat Mitigation Status
Private key in React state (DevTools exposure) Stored in useRef, not useState FIXED
Key leak on unmount Ref cleared in cleanup effect FIXED
Key leak on app background (iOS screenshot) Ref + display state cleared on visibilitychange FIXED
Clipboard leak on paste navigator.clipboard.writeText('') after paste FIXED
Pending ref not cleared after success clearState() zeroes pendingMnemonicRef and pendingImportModeRef FIXED
Invalid key accepted 3-layer validation: regex (64 hex), fromHex(), DirectSecp256k1Wallet.fromKey() SECURE
Error messages leak key material Generic errors only ("Invalid private key") SECURE
Encryption at rest Same AES-256-GCM + PBKDF2 (1M iterations) as mnemonic SECURE
Password brute force 8+ chars, 3/4 character classes if < 12 chars ADEQUATE
Key type disclosure in Redux keys: 'private-key' visible in Redux — accepted (no key material) ACCEPTED
Tauri device key in localStorage Pre-existing design trade-off, not changed ACCEPTED
Auto-lock timer disabled Pre-existing, not changed (MNEMONIC_AUTO_CLEAR_MS unused) ACCEPTED

Encryption Format

Private key hex string is encrypted with identical format as mnemonic:

version(1 byte) + salt(16 bytes) + iv(12 bytes) + AES-GCM-256(plaintext)
→ base64 encoded → localStorage['cyb:mnemonic:{address}']

The decryptMnemonic() function is format-agnostic — it returns any stored plaintext. The account type (keys field in Redux) determines whether to call getOfflineSignerFromMnemonic() or getOfflineSignerFromPrivateKey().

CosmJS Validation Chain

  1. fromHex(privkeyHex) — validates hex format, throws on non-hex or odd-length
  2. DirectSecp256k1Wallet.fromKey(privkey) — validates 32-byte length, validates against secp256k1 curve order
  3. Secp256k1Wallet.fromKey(privkey) — same validation for Amino signer

All three layers throw before any storage occurs.

signArbitrary (ADR-036)

CybPrivateKeySigner.signArbitrary() composes Secp256k1Wallet (Amino) for ADR-036 signing — same MsgSignData format as CybOfflineSigner. The hasSignArbitrary() type guard works via duck-typing (typeof signer.signArbitrary === 'function').

Findings Fixed Before Commit

  1. CRITICAL: Moved privateKeyHex from useState to useRef — prevents React DevTools exposure
  2. CRITICAL: Added ref cleanup on unmount
  3. HIGH: Added ref + display cleanup on visibilitychange (background)
  4. HIGH: Added clipboard clearing on private key paste
  5. HIGH: Added pendingImportModeRef reset in clearState()

Accepted Risks

  • Device key for Tauri auto-unlock stored in localStorage (pre-existing, not introduced by this change)
  • No auto-lock timer (pre-existing design decision)
  • Account type visible in Redux state (information disclosure only, no key material)

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