DownloadBack up your encryption key
End-to-end encryption is set up automatically when you create your Commingle account. Most of your personal and financial data is already protected.
Open the menu
Tap the menu button in the top-right corner of the Home screen.
Go to encryption
Open End-to-end encryption, located just below your profile.
How most apps may see your data?
| ID | Date | Title | Amount | Category |
|---|---|---|---|---|
| 1 | 23 Aug | Rent | −$1850 | Household |
| 2 | 24 Aug | Salary | +$6,200 | Work |
| 3 | 24 Aug | Dinner | −$84.50 | Food |
The database contains readable financial data. Anyone who gains sufficient access to it may be able to understand your transactions – whether through authorised access, a mistake or a data breach.
What does Commingle see?
| ID | Nonce1 | Key2 | Data |
|---|---|---|---|
| 1 | 7f2a91... | b91c4e... | 4b8e0c91d7fa... |
| 2 | c1843d... | 3d07a2... | a07f39bc82e1... |
| 3 | 92e6ab... | e58f16... | f31d8a04c927... |
This is what leaves your device. Only the encryption key stored on your devices can turn this noise back into meaningful financial data. Commingle has no way of knowing whether you’re spending a few dollars or moving millions.
Nonce – a random value used during encryption, ensuring that even identical transactions, like your daily coffee, produce completely different encrypted data.
Encrypted key – a unique, securely generated key used to encrypt this transaction. It is itself encrypted with your public key and can only be unlocked with your private key.
What is E2E-encrypted?
Transactions
Notifications
Friend balances
Organisation
Charts & summaries
Settings & preferences
Does Commingle use military-grade encryption?
Yeah… military-grade. The term used by almost every website trying to make encryption sound fancy. Yes, Commingle uses what is often marketed as “military-grade encryption”. We prefer to call it industry-standard cryptography. The same well-established cryptographic building blocks are used everywhere – from banking systems to your local supermarket’s loyalty app. Where there is a meaningful choice, we opt for the stronger end of current recommendations – for example, AES-256 rather than AES-128. With today’s computers, properly implemented modern encryption is not realistically breakable by brute force. If you’d like to see just how absurdly large the numbers involved become, this video gives a fun illustration.
Quantum computers and “harvest now, decrypt later” are legitimate long-term concerns, although we don’t expect anyone to build a futuristic, enormously expensive machine specifically to uncover your grocery spending. We keep up with evolving cryptographic recommendations and will evolve Commingle’s encryption as new threats and standards emerge.
Where’s the catch?
There isn’t one. We really can’t see your transactions – and we don’t want to.
Since day one, Commingle has been built around a privacy-first principle. We’d rather be funded by our users through subscriptions than monetise your financial data by selling it to advertisers.
We also want to sleep peacefully at night. If we ever slip up and our database leaks, your transactions remain encrypted. That protects you, and it protects us from losing your trust – or facing some very unpleasant fines.
Caution: Technical jargon
How does end-to-end encryption work?
The following section describes Commingle’s cryptographic design for readers interested in the technical implementation.
Identity and key management
During registration, Commingle generates an X25519 public/private key pair directly on your device.
Your public key is uploaded to Commingle’s servers so other devices can encrypt data for you.
Your private key never leaves your device in plaintext. Once unlocked, it is stored securely using your operating system’s secure storage.
Setting up a new device
To protect your private key from loss and allow you to retrieve it on a new device, you can choose to securely store an encrypted backup on Commingle’s servers. You choose a password to protect this backup. Commingle derives an encryption key from your password using Argon2id and encrypts the backup with AES-256-GCM. Your password and unencrypted private key are never sent to Commingle’s servers.
Argon2id is intentionally memory-hard and computationally expensive, making brute-force attacks impractical. This operation happens only once when unlocking your key, not every time you access your data.
Commingle never knows your password and cannot recover your private key if the password is lost.
Encrypting your financial metadata
Categories, wallets, events, chart settings and other financial metadata are serialised as JSON directly on your device before being encrypted with AES-256-GCM.
The encryption key is deterministically derived from your unlocked private key using HKDF-SHA256.
Commingle stores only encrypted ciphertext. Names, icons, colours, balances, settings and other readable information never appear on the server in plaintext.
Encrypting your transactions
Transactions use envelope encryption.
For every transaction, Commingle generates a unique random 256-bit content key and encrypts the transaction using AES-256-GCM. The content key is then encrypted separately for each authorised participant using their X25519 public key.
Only participants holding the corresponding private keys can recover the content key and decrypt the transaction. Adding or removing participants controls who can access its contents.
Commingle can process only the minimum structural metadata required to synchronise transactions between authorised participants. Transaction titles, amounts, currencies, notes, categories and other protected fields remain end-to-end encrypted and unreadable to Commingle.
Encrypting your friend balances
Your balances with friends are kept in a shared, end-to-end encrypted ledger. The ledger contains the current amounts owed between you and each of your friends, per currency – not the transactions that created those balances.
Your device encrypts the ledger using AES-256-GCM with its own random 256-bit content key. That key is protected using X25519 and HKDF-SHA256 and can be opened only by devices holding an authorised private key. A fresh nonce is used whenever the ledger is updated.
Unlike your other data, the ledger is intentionally shared with your entire friend circle. Each of your friends receives an individually encrypted copy of the key needed to open and update it. Commingle only displays each friend’s own balance with you, but because your friends hold the key to the shared ledger, a technically capable friend could access the other balances it contains. The ledger never contains the transactions, titles, notes or categories behind those balances.
When a split transaction changes a balance, the calculation happens on a participant’s device. The affected ledger is decrypted, updated and encrypted again before being uploaded. Commingle stores and synchronises the encrypted ledger but cannot read the amounts inside it.
Encrypting your notifications
Notifications about shared activity originate on the device of the person who caused the change. The notification title and message are encrypted for the recipient before they leave that device using X25519, HKDF-SHA256 and AES-256-GCM.
Each notification is encrypted specifically for its recipient. Only the recipient’s private key can decrypt its contents. Commingle simply forwards the encrypted notification to Apple or Google for delivery – neither Commingle nor the delivery provider can read what the notification actually says.
Important to know
Analytics
We collect anonymous analytics to understand how people use Commingle and improve the app over time. Analytics never include your identity, transaction descriptions, receipt contents or individual transaction amounts. We may group users into broad, anonymous segments – for example, based on region or net worth range – to understand how different groups use Commingle’s features and help us make the app more useful for everyone.
AI Features
Commingle offers AI-powered features such as receipt scanning, voice transaction entry and automatic transaction categorisation to make managing your finances easier. When you choose to use one of these features, only the information required to process your request is securely sent to an AI provider. This may include a limited subset of your personal and financial data.
