hoangifp / securenotes

SecureNotes

Welcome to SecureNotes.

SecureNotes lets the user store text notes securely. All notes are encrypted with AES-GCM 256 before being stored in the database.

The key to decrypt notes is formed by the user's password; therefore, only the user can decrypt the saved notes.

Demo

Click on image below for the product video demo.

Supported platforms & Set up

• iOS 13 and later.
• Xcode 12 and later.

Set up

The Cocoapods dependency manager is required to set up the project dependencies.

If Cocoapods is already available, then download the SecureNotes project from Github and run the below command.

cd SecureNotes
pod install

Features & Cryptography

Cryptography Used

• AES-GCM
• AES-CBC
• SHA256
• SHA512
• eciesEncryptionCofactorVariableIVX963SHA256AESGCM

Register, Key forming

salt = random(32 bytes) // To be encrypted by ecies and stored in db
data = Data(salt+username+pin)
iv = random(32 bytes) // To be encrypted by ecies and stored in db
key = data.sha256()
aes = AES-GCM(key, iv)

hash = data.sha512() // To be encrypted by ecies and stored in db

For demonstration purposes, sha256 is used to derive the key. However, PBKDF2 should be used to protect against brute force.

After successful login/registering, the AES-GCM key will be formed and stay encrypted in the memory during the active session by Secure Enclave eciesEncryptionCofactorVariableIVX963SHA256AESGCM (EC*). It acts as a caching algorithm to be re-used multiple times without additional login from the user. If the application is transitioned to background or is terminated, the encrypted EC(AES-GCM key, IV) will be wiped out from memory.

SecureEnclave.generateKeyPair()
// Caching keys in memory
encrypted = SecureEnclave.encrypt(key)
encrypted = SecureEncalve.encrypt(IV)

Login with username + pin

encryptedSalt = datbase(encryptedSalt)
salt = SecureEnclave.decrypt(encryptedSalt)

encryptedHash = datbase(encryptedHash)
hash = SecureEnclave.decrypt(encryptedHash)

data = Data(salt+username+pin)
loginHash = data.sha512()

if loginHash == hash {
    key = data.sha256()
    encryptedKey = SecureEnclave.encrypt(key)
    encryptedIV = Database(encryptedIV)
} else {
    //Wrong Username or Password
}

Enable Biometric

The biometric authentication mode is not activated by default.

The EC(AES-GCM key) will need to be securely stored in the database if the user wants to use the 'login with the Biometric' feature

First, the system generates a new random AES-CBC symmetric key.

Once the new AES-CBC key is created, the EC(AES-GCM key) will be encrypted with AES-CBC key

The final AES-CBC(EC(AES-GCM key)) will be stored in the database for later access.

The new AES-CBC symmetric key to decrypt the AES-CBC(EC(AES-GCM key)) will be locked inside Keychain and only be accessible with the user's presence (Biometrics authentication)

bioIV = random(16 bytes) // To be encrypted by ecies and stored in db
bioKey = random(16 bytes)
bioServiceId = random(32 bytes) // To be encrypted by ecies and stored in db

// Store AES-CBC key to the keychain that requires user's presence
KeyChainBiometric.add(bioKey, serviceId: bioServiceId)

aes = AES-CBC(bioIV, bioKey)
encryptedMasterKey = aes.encrypt(encryptedKey) // To store in db

Login with Biometric

encryptedBioServiceId = Database(encryptedBioServiceId)
bioServiceId = SecureEnclave.decrypt(encryptedBioServiceId)

encryptedBioIV = Database(encryptedBioIV)
bioIV = SecureEnclave.decrypt(encryptedBioIV)

// This key requires the user's presence to read
bioKey = KeyChainBiometric.read(bioServiceId)

aes = AES-CBC(bioIV, bioKey)
encryptedMasterKey = Database(encryptedMasterKey)

// Caching keys in memory
encryptedKey = aes.decrypt(encryptedMasterKey)
encryptedIV = Database(encryptedIV)

Sequence Diagram

Security Discussion:

The application has been enforced by some security protections in the RELEASE build:

• Show warning to jailbreak devices
• Anti-debug for some important functions
• Anti-hook for some important functions

Below methods can be implemented for the application's further protection:

• Hide hardcoded strings, add more control flows and rename sensitive functions/variables to hide attack points during static analysis.
• Add a secure keypad to protect the pin against the keyboard logger.
• Add anti-tampering.
• Use MEDL and Zcrambler to implement RASP.

Testing

Because of the time constraints, automatic tests are not included.