Security & data

Private by design, not by policy.

Your passphrase encrypts your financial data. A stolen copy of our database is unreadable.

How your encryption works.

When you create your Pennyweight account, you choose a passphrase. Your browser derives an encryption key from it, and your financial data is encrypted with that key before it is stored. A stolen copy of our database is unreadable: merchants, amounts, balances, and account numbers are ciphertext.

What a session means.

Our servers can decrypt your data only during your active session — to answer your AI's requests and to sync your bank. Outside a session there is no key on our side to decrypt with. Your AI assistant never holds your keys: it gets an opaque token, and our server decrypts on-demand for the tool calls you ask for.

Passphrase and recovery code.

Setup gives you a recovery code. It is the second way in: if you forget your passphrase, the recovery code restores access. Lose both and no one can recover your data — not you, not us. Save the recovery code somewhere you will still have it in a year.

Multi-entity, same security.

Every entity you create in Pennyweight inherits the same encryption. Your freelance books and your personal spending are encrypted under the same key and stored separately. Entity separation is enforced at the data layer, not just the UI.

How Plaid works.

Pennyweight uses Plaid to securely read transactions and balances from the accounts you choose to connect. We never see or store your bank login credentials. Plaid handles that connection directly with your bank. Plaid is the same infrastructure used by Venmo, Robinhood, and thousands of financial apps. We request read-only access only. Pennyweight cannot move money, make payments, or modify your accounts in any way.

What an attacker sees.

If someone walked off with our database, here is what they would get. The full list, including the parts we would rather not have on it.

FieldStatusWhy

Merchants, descriptions, amounts, balances, account numbers, notes, uploaded statementsEncryptedAES-256-GCM under a key derived from your passphrase. Without the passphrase, random bytes.

Wrapped encryption keysEncryptedYour key is sealed under your passphrase. An attacker would have to break every user’s passphrase individually.

Spending categories, transaction dates, currency, which rows share an accountReadableStructure we query on, kept outside the envelope. It shows shape and timing, not who you paid or how much.

Bank names and ledger namesReadableWhich institutions you connected and what you named each set of books. We are encrypting both.

What we don’t do.

We don’t sell your data.
We don’t share it with advertisers.
We don’t use it to train models across users.
We don’t store your bank credentials.
We don’t decrypt your data outside your active session.

Audit trail.

Every change an AI makes to your data is logged: which tool ran, when, and why. Human-review checkpoints exist before any irreversible operation touches your books, and your ledger keeps a history you can review at any time. The structural record — which tool, which account, what time — is readable without your key, because that is what lets us show you the log. The substance of each entry, including the amounts and merchants involved and the assistant's stated reasoning, is encrypted under your key like the rest of your data.

Cross-platform, same trust.

Your encryption works the same whether you use Pennyweight through any AI assistant — Claude, ChatGPT, Gemini, Grok, or any MCP client — or the web dashboard. Every client authorizes against the same session model, so your data isn't locked to one platform and the security model doesn't change based on where you access it.